mv compiler to compiler/

compiler/rustc_lint/src/array_into_iter.rs

@@ -0,0 +1,97 @@
+use crate::{LateContext, LateLintPass, LintContext};
+use rustc_errors::Applicability;
+use rustc_hir as hir;
+use rustc_middle::ty;
+use rustc_middle::ty::adjustment::{Adjust, Adjustment};
+use rustc_session::lint::FutureIncompatibleInfo;
+use rustc_span::symbol::sym;
+
+declare_lint! {
+    pub ARRAY_INTO_ITER,
+    Warn,
+    "detects calling `into_iter` on arrays",
+    @future_incompatible = FutureIncompatibleInfo {
+        reference: "issue #66145 <https://github.com/rust-lang/rust/issues/66145>",
+        edition: None,
+    };
+}
+
+declare_lint_pass!(
+    /// Checks for instances of calling `into_iter` on arrays.
+    ArrayIntoIter => [ARRAY_INTO_ITER]
+);
+
+impl<'tcx> LateLintPass<'tcx> for ArrayIntoIter {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
+        // We only care about method call expressions.
+        if let hir::ExprKind::MethodCall(call, span, args, _) = &expr.kind {
+            if call.ident.name != sym::into_iter {
+                return;
+            }
+
+            // Check if the method call actually calls the libcore
+            // `IntoIterator::into_iter`.
+            let def_id = cx.typeck_results().type_dependent_def_id(expr.hir_id).unwrap();
+            match cx.tcx.trait_of_item(def_id) {
+                Some(trait_id) if cx.tcx.is_diagnostic_item(sym::IntoIterator, trait_id) => {}
+                _ => return,
+            };
+
+            // As this is a method call expression, we have at least one
+            // argument.
+            let receiver_arg = &args[0];
+
+            // Peel all `Box<_>` layers. We have to special case `Box` here as
+            // `Box` is the only thing that values can be moved out of via
+            // method call. `Box::new([1]).into_iter()` should trigger this
+            // lint.
+            let mut recv_ty = cx.typeck_results().expr_ty(receiver_arg);
+            let mut num_box_derefs = 0;
+            while recv_ty.is_box() {
+                num_box_derefs += 1;
+                recv_ty = recv_ty.boxed_ty();
+            }
+
+            // Make sure we found an array after peeling the boxes.
+            if !matches!(recv_ty.kind, ty::Array(..)) {
+                return;
+            }
+
+            // Make sure that there is an autoref coercion at the expected
+            // position. The first `num_box_derefs` adjustments are the derefs
+            // of the box.
+            match cx.typeck_results().expr_adjustments(receiver_arg).get(num_box_derefs) {
+                Some(Adjustment { kind: Adjust::Borrow(_), .. }) => {}
+                _ => return,
+            }
+
+            // Emit lint diagnostic.
+            let target = match cx.typeck_results().expr_ty_adjusted(receiver_arg).kind {
+                ty::Ref(_, ty::TyS { kind: ty::Array(..), .. }, _) => "[T; N]",
+                ty::Ref(_, ty::TyS { kind: ty::Slice(..), .. }, _) => "[T]",
+
+                // We know the original first argument type is an array type,
+                // we know that the first adjustment was an autoref coercion
+                // and we know that `IntoIterator` is the trait involved. The
+                // array cannot be coerced to something other than a reference
+                // to an array or to a slice.
+                _ => bug!("array type coerced to something other than array or slice"),
+            };
+            cx.struct_span_lint(ARRAY_INTO_ITER, *span, |lint| {
+                lint.build(&format!(
+                "this method call currently resolves to `<&{} as IntoIterator>::into_iter` (due \
+                    to autoref coercions), but that might change in the future when \
+                    `IntoIterator` impls for arrays are added.",
+                target,
+                ))
+                .span_suggestion(
+                    call.ident.span,
+                    "use `.iter()` instead of `.into_iter()` to avoid ambiguity",
+                    "iter".into(),
+                    Applicability::MachineApplicable,
+                )
+                .emit();
+            })
+        }
+    }
+}

compiler/rustc_lint/src/context.rs

@@ -0,0 +1,862 @@
+//! Implementation of lint checking.
+//!
+//! The lint checking is mostly consolidated into one pass which runs
+//! after all other analyses. Throughout compilation, lint warnings
+//! can be added via the `add_lint` method on the Session structure. This
+//! requires a span and an ID of the node that the lint is being added to. The
+//! lint isn't actually emitted at that time because it is unknown what the
+//! actual lint level at that location is.
+//!
+//! To actually emit lint warnings/errors, a separate pass is used.
+//! A context keeps track of the current state of all lint levels.
+//! Upon entering a node of the ast which can modify the lint settings, the
+//! previous lint state is pushed onto a stack and the ast is then recursed
+//! upon. As the ast is traversed, this keeps track of the current lint level
+//! for all lint attributes.
+
+use self::TargetLint::*;
+
+use crate::levels::LintLevelsBuilder;
+use crate::passes::{EarlyLintPassObject, LateLintPassObject};
+use rustc_ast as ast;
+use rustc_ast::util::lev_distance::find_best_match_for_name;
+use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::sync;
+use rustc_errors::{struct_span_err, Applicability};
+use rustc_hir as hir;
+use rustc_hir::def::Res;
+use rustc_hir::def_id::{CrateNum, DefId};
+use rustc_hir::definitions::{DefPathData, DisambiguatedDefPathData};
+use rustc_middle::lint::LintDiagnosticBuilder;
+use rustc_middle::middle::privacy::AccessLevels;
+use rustc_middle::middle::stability;
+use rustc_middle::ty::layout::{LayoutError, TyAndLayout};
+use rustc_middle::ty::{self, print::Printer, subst::GenericArg, Ty, TyCtxt};
+use rustc_session::lint::{add_elided_lifetime_in_path_suggestion, BuiltinLintDiagnostics};
+use rustc_session::lint::{FutureIncompatibleInfo, Level, Lint, LintBuffer, LintId};
+use rustc_session::Session;
+use rustc_span::{symbol::Symbol, MultiSpan, Span, DUMMY_SP};
+use rustc_target::abi::LayoutOf;
+
+use std::cell::Cell;
+use std::slice;
+
+/// Information about the registered lints.
+///
+/// This is basically the subset of `Context` that we can
+/// build early in the compile pipeline.
+pub struct LintStore {
+    /// Registered lints.
+    lints: Vec<&'static Lint>,
+
+    /// Constructor functions for each variety of lint pass.
+    ///
+    /// These should only be called once, but since we want to avoid locks or
+    /// interior mutability, we don't enforce this (and lints should, in theory,
+    /// be compatible with being constructed more than once, though not
+    /// necessarily in a sane manner. This is safe though.)
+    pub pre_expansion_passes: Vec<Box<dyn Fn() -> EarlyLintPassObject + sync::Send + sync::Sync>>,
+    pub early_passes: Vec<Box<dyn Fn() -> EarlyLintPassObject + sync::Send + sync::Sync>>,
+    pub late_passes: Vec<Box<dyn Fn() -> LateLintPassObject + sync::Send + sync::Sync>>,
+    /// This is unique in that we construct them per-module, so not once.
+    pub late_module_passes: Vec<Box<dyn Fn() -> LateLintPassObject + sync::Send + sync::Sync>>,
+
+    /// Lints indexed by name.
+    by_name: FxHashMap<String, TargetLint>,
+
+    /// Map of registered lint groups to what lints they expand to.
+    lint_groups: FxHashMap<&'static str, LintGroup>,
+}
+
+/// The target of the `by_name` map, which accounts for renaming/deprecation.
+enum TargetLint {
+    /// A direct lint target
+    Id(LintId),
+
+    /// Temporary renaming, used for easing migration pain; see #16545
+    Renamed(String, LintId),
+
+    /// Lint with this name existed previously, but has been removed/deprecated.
+    /// The string argument is the reason for removal.
+    Removed(String),
+}
+
+pub enum FindLintError {
+    NotFound,
+    Removed,
+}
+
+struct LintAlias {
+    name: &'static str,
+    /// Whether deprecation warnings should be suppressed for this alias.
+    silent: bool,
+}
+
+struct LintGroup {
+    lint_ids: Vec<LintId>,
+    from_plugin: bool,
+    depr: Option<LintAlias>,
+}
+
+pub enum CheckLintNameResult<'a> {
+    Ok(&'a [LintId]),
+    /// Lint doesn't exist. Potentially contains a suggestion for a correct lint name.
+    NoLint(Option<Symbol>),
+    /// The lint is either renamed or removed. This is the warning
+    /// message, and an optional new name (`None` if removed).
+    Warning(String, Option<String>),
+    /// The lint is from a tool. If the Option is None, then either
+    /// the lint does not exist in the tool or the code was not
+    /// compiled with the tool and therefore the lint was never
+    /// added to the `LintStore`. Otherwise the `LintId` will be
+    /// returned as if it where a rustc lint.
+    Tool(Result<&'a [LintId], (Option<&'a [LintId]>, String)>),
+}
+
+impl LintStore {
+    pub fn new() -> LintStore {
+        LintStore {
+            lints: vec![],
+            pre_expansion_passes: vec![],
+            early_passes: vec![],
+            late_passes: vec![],
+            late_module_passes: vec![],
+            by_name: Default::default(),
+            lint_groups: Default::default(),
+        }
+    }
+
+    pub fn get_lints<'t>(&'t self) -> &'t [&'static Lint] {
+        &self.lints
+    }
+
+    pub fn get_lint_groups<'t>(&'t self) -> Vec<(&'static str, Vec<LintId>, bool)> {
+        self.lint_groups
+            .iter()
+            .filter(|(_, LintGroup { depr, .. })| {
+                // Don't display deprecated lint groups.
+                depr.is_none()
+            })
+            .map(|(k, LintGroup { lint_ids, from_plugin, .. })| {
+                (*k, lint_ids.clone(), *from_plugin)
+            })
+            .collect()
+    }
+
+    pub fn register_early_pass(
+        &mut self,
+        pass: impl Fn() -> EarlyLintPassObject + 'static + sync::Send + sync::Sync,
+    ) {
+        self.early_passes.push(Box::new(pass));
+    }
+
+    pub fn register_pre_expansion_pass(
+        &mut self,
+        pass: impl Fn() -> EarlyLintPassObject + 'static + sync::Send + sync::Sync,
+    ) {
+        self.pre_expansion_passes.push(Box::new(pass));
+    }
+
+    pub fn register_late_pass(
+        &mut self,
+        pass: impl Fn() -> LateLintPassObject + 'static + sync::Send + sync::Sync,
+    ) {
+        self.late_passes.push(Box::new(pass));
+    }
+
+    pub fn register_late_mod_pass(
+        &mut self,
+        pass: impl Fn() -> LateLintPassObject + 'static + sync::Send + sync::Sync,
+    ) {
+        self.late_module_passes.push(Box::new(pass));
+    }
+
+    // Helper method for register_early/late_pass
+    pub fn register_lints(&mut self, lints: &[&'static Lint]) {
+        for lint in lints {
+            self.lints.push(lint);
+
+            let id = LintId::of(lint);
+            if self.by_name.insert(lint.name_lower(), Id(id)).is_some() {
+                bug!("duplicate specification of lint {}", lint.name_lower())
+            }
+
+            if let Some(FutureIncompatibleInfo { edition, .. }) = lint.future_incompatible {
+                if let Some(edition) = edition {
+                    self.lint_groups
+                        .entry(edition.lint_name())
+                        .or_insert(LintGroup {
+                            lint_ids: vec![],
+                            from_plugin: lint.is_plugin,
+                            depr: None,
+                        })
+                        .lint_ids
+                        .push(id);
+                }
+
+                self.lint_groups
+                    .entry("future_incompatible")
+                    .or_insert(LintGroup {
+                        lint_ids: vec![],
+                        from_plugin: lint.is_plugin,
+                        depr: None,
+                    })
+                    .lint_ids
+                    .push(id);
+            }
+        }
+    }
+
+    pub fn register_group_alias(&mut self, lint_name: &'static str, alias: &'static str) {
+        self.lint_groups.insert(
+            alias,
+            LintGroup {
+                lint_ids: vec![],
+                from_plugin: false,
+                depr: Some(LintAlias { name: lint_name, silent: true }),
+            },
+        );
+    }
+
+    pub fn register_group(
+        &mut self,
+        from_plugin: bool,
+        name: &'static str,
+        deprecated_name: Option<&'static str>,
+        to: Vec<LintId>,
+    ) {
+        let new = self
+            .lint_groups
+            .insert(name, LintGroup { lint_ids: to, from_plugin, depr: None })
+            .is_none();
+        if let Some(deprecated) = deprecated_name {
+            self.lint_groups.insert(
+                deprecated,
+                LintGroup {
+                    lint_ids: vec![],
+                    from_plugin,
+                    depr: Some(LintAlias { name, silent: false }),
+                },
+            );
+        }
+
+        if !new {
+            bug!("duplicate specification of lint group {}", name);
+        }
+    }
+
+    pub fn register_renamed(&mut self, old_name: &str, new_name: &str) {
+        let target = match self.by_name.get(new_name) {
+            Some(&Id(lint_id)) => lint_id,
+            _ => bug!("invalid lint renaming of {} to {}", old_name, new_name),
+        };
+        self.by_name.insert(old_name.to_string(), Renamed(new_name.to_string(), target));
+    }
+
+    pub fn register_removed(&mut self, name: &str, reason: &str) {
+        self.by_name.insert(name.into(), Removed(reason.into()));
+    }
+
+    pub fn find_lints(&self, mut lint_name: &str) -> Result<Vec<LintId>, FindLintError> {
+        match self.by_name.get(lint_name) {
+            Some(&Id(lint_id)) => Ok(vec![lint_id]),
+            Some(&Renamed(_, lint_id)) => Ok(vec![lint_id]),
+            Some(&Removed(_)) => Err(FindLintError::Removed),
+            None => loop {
+                return match self.lint_groups.get(lint_name) {
+                    Some(LintGroup { lint_ids, depr, .. }) => {
+                        if let Some(LintAlias { name, .. }) = depr {
+                            lint_name = name;
+                            continue;
+                        }
+                        Ok(lint_ids.clone())
+                    }
+                    None => Err(FindLintError::Removed),
+                };
+            },
+        }
+    }
+
+    /// Checks the validity of lint names derived from the command line
+    pub fn check_lint_name_cmdline(&self, sess: &Session, lint_name: &str, level: Level) {
+        let db = match self.check_lint_name(lint_name, None) {
+            CheckLintNameResult::Ok(_) => None,
+            CheckLintNameResult::Warning(ref msg, _) => Some(sess.struct_warn(msg)),
+            CheckLintNameResult::NoLint(suggestion) => {
+                let mut err =
+                    struct_span_err!(sess, DUMMY_SP, E0602, "unknown lint: `{}`", lint_name);
+
+                if let Some(suggestion) = suggestion {
+                    err.help(&format!("did you mean: `{}`", suggestion));
+                }
+
+                Some(err)
+            }
+            CheckLintNameResult::Tool(result) => match result {
+                Err((Some(_), new_name)) => Some(sess.struct_warn(&format!(
+                    "lint name `{}` is deprecated \
+                     and does not have an effect anymore. \
+                     Use: {}",
+                    lint_name, new_name
+                ))),
+                _ => None,
+            },
+        };
+
+        if let Some(mut db) = db {
+            let msg = format!(
+                "requested on the command line with `{} {}`",
+                match level {
+                    Level::Allow => "-A",
+                    Level::Warn => "-W",
+                    Level::Deny => "-D",
+                    Level::Forbid => "-F",
+                },
+                lint_name
+            );
+            db.note(&msg);
+            db.emit();
+        }
+    }
+
+    /// Checks the name of a lint for its existence, and whether it was
+    /// renamed or removed. Generates a DiagnosticBuilder containing a
+    /// warning for renamed and removed lints. This is over both lint
+    /// names from attributes and those passed on the command line. Since
+    /// it emits non-fatal warnings and there are *two* lint passes that
+    /// inspect attributes, this is only run from the late pass to avoid
+    /// printing duplicate warnings.
+    pub fn check_lint_name(
+        &self,
+        lint_name: &str,
+        tool_name: Option<Symbol>,
+    ) -> CheckLintNameResult<'_> {
+        let complete_name = if let Some(tool_name) = tool_name {
+            format!("{}::{}", tool_name, lint_name)
+        } else {
+            lint_name.to_string()
+        };
+        // If the lint was scoped with `tool::` check if the tool lint exists
+        if tool_name.is_some() {
+            match self.by_name.get(&complete_name) {
+                None => match self.lint_groups.get(&*complete_name) {
+                    None => return CheckLintNameResult::Tool(Err((None, String::new()))),
+                    Some(LintGroup { lint_ids, .. }) => {
+                        return CheckLintNameResult::Tool(Ok(&lint_ids));
+                    }
+                },
+                Some(&Id(ref id)) => return CheckLintNameResult::Tool(Ok(slice::from_ref(id))),
+                // If the lint was registered as removed or renamed by the lint tool, we don't need
+                // to treat tool_lints and rustc lints different and can use the code below.
+                _ => {}
+            }
+        }
+        match self.by_name.get(&complete_name) {
+            Some(&Renamed(ref new_name, _)) => CheckLintNameResult::Warning(
+                format!("lint `{}` has been renamed to `{}`", complete_name, new_name),
+                Some(new_name.to_owned()),
+            ),
+            Some(&Removed(ref reason)) => CheckLintNameResult::Warning(
+                format!("lint `{}` has been removed: `{}`", complete_name, reason),
+                None,
+            ),
+            None => match self.lint_groups.get(&*complete_name) {
+                // If neither the lint, nor the lint group exists check if there is a `clippy::`
+                // variant of this lint
+                None => self.check_tool_name_for_backwards_compat(&complete_name, "clippy"),
+                Some(LintGroup { lint_ids, depr, .. }) => {
+                    // Check if the lint group name is deprecated
+                    if let Some(LintAlias { name, silent }) = depr {
+                        let LintGroup { lint_ids, .. } = self.lint_groups.get(name).unwrap();
+                        return if *silent {
+                            CheckLintNameResult::Ok(&lint_ids)
+                        } else {
+                            CheckLintNameResult::Tool(Err((Some(&lint_ids), (*name).to_string())))
+                        };
+                    }
+                    CheckLintNameResult::Ok(&lint_ids)
+                }
+            },
+            Some(&Id(ref id)) => CheckLintNameResult::Ok(slice::from_ref(id)),
+        }
+    }
+
+    fn check_tool_name_for_backwards_compat(
+        &self,
+        lint_name: &str,
+        tool_name: &str,
+    ) -> CheckLintNameResult<'_> {
+        let complete_name = format!("{}::{}", tool_name, lint_name);
+        match self.by_name.get(&complete_name) {
+            None => match self.lint_groups.get(&*complete_name) {
+                // Now we are sure, that this lint exists nowhere
+                None => {
+                    let symbols =
+                        self.by_name.keys().map(|name| Symbol::intern(&name)).collect::<Vec<_>>();
+
+                    let suggestion = find_best_match_for_name(
+                        symbols.iter(),
+                        Symbol::intern(&lint_name.to_lowercase()),
+                        None,
+                    );
+
+                    CheckLintNameResult::NoLint(suggestion)
+                }
+                Some(LintGroup { lint_ids, depr, .. }) => {
+                    // Reaching this would be weird, but let's cover this case anyway
+                    if let Some(LintAlias { name, silent }) = depr {
+                        let LintGroup { lint_ids, .. } = self.lint_groups.get(name).unwrap();
+                        return if *silent {
+                            CheckLintNameResult::Tool(Err((Some(&lint_ids), complete_name)))
+                        } else {
+                            CheckLintNameResult::Tool(Err((Some(&lint_ids), (*name).to_string())))
+                        };
+                    }
+                    CheckLintNameResult::Tool(Err((Some(&lint_ids), complete_name)))
+                }
+            },
+            Some(&Id(ref id)) => {
+                CheckLintNameResult::Tool(Err((Some(slice::from_ref(id)), complete_name)))
+            }
+            _ => CheckLintNameResult::NoLint(None),
+        }
+    }
+}
+
+/// Context for lint checking after type checking.
+pub struct LateContext<'tcx> {
+    /// Type context we're checking in.
+    pub tcx: TyCtxt<'tcx>,
+
+    /// Current body, or `None` if outside a body.
+    pub enclosing_body: Option<hir::BodyId>,
+
+    /// Type-checking results for the current body. Access using the `typeck_results`
+    /// and `maybe_typeck_results` methods, which handle querying the typeck results on demand.
+    // FIXME(eddyb) move all the code accessing internal fields like this,
+    // to this module, to avoid exposing it to lint logic.
+    pub(super) cached_typeck_results: Cell<Option<&'tcx ty::TypeckResults<'tcx>>>,
+
+    /// Parameter environment for the item we are in.
+    pub param_env: ty::ParamEnv<'tcx>,
+
+    /// Items accessible from the crate being checked.
+    pub access_levels: &'tcx AccessLevels,
+
+    /// The store of registered lints and the lint levels.
+    pub lint_store: &'tcx LintStore,
+
+    pub last_node_with_lint_attrs: hir::HirId,
+
+    /// Generic type parameters in scope for the item we are in.
+    pub generics: Option<&'tcx hir::Generics<'tcx>>,
+
+    /// We are only looking at one module
+    pub only_module: bool,
+}
+
+/// Context for lint checking of the AST, after expansion, before lowering to
+/// HIR.
+pub struct EarlyContext<'a> {
+    /// Type context we're checking in.
+    pub sess: &'a Session,
+
+    /// The crate being checked.
+    pub krate: &'a ast::Crate,
+
+    pub builder: LintLevelsBuilder<'a>,
+
+    /// The store of registered lints and the lint levels.
+    pub lint_store: &'a LintStore,
+
+    pub buffered: LintBuffer,
+}
+
+pub trait LintPassObject: Sized {}
+
+impl LintPassObject for EarlyLintPassObject {}
+
+impl LintPassObject for LateLintPassObject {}
+
+pub trait LintContext: Sized {
+    type PassObject: LintPassObject;
+
+    fn sess(&self) -> &Session;
+    fn lints(&self) -> &LintStore;
+
+    fn lookup_with_diagnostics(
+        &self,
+        lint: &'static Lint,
+        span: Option<impl Into<MultiSpan>>,
+        decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
+        diagnostic: BuiltinLintDiagnostics,
+    ) {
+        self.lookup(lint, span, |lint| {
+            // We first generate a blank diagnostic.
+            let mut db = lint.build("");
+
+            // Now, set up surrounding context.
+            let sess = self.sess();
+            match diagnostic {
+                BuiltinLintDiagnostics::Normal => (),
+                BuiltinLintDiagnostics::BareTraitObject(span, is_global) => {
+                    let (sugg, app) = match sess.source_map().span_to_snippet(span) {
+                        Ok(s) if is_global => {
+                            (format!("dyn ({})", s), Applicability::MachineApplicable)
+                        }
+                        Ok(s) => (format!("dyn {}", s), Applicability::MachineApplicable),
+                        Err(_) => ("dyn <type>".to_string(), Applicability::HasPlaceholders),
+                    };
+                    db.span_suggestion(span, "use `dyn`", sugg, app);
+                }
+                BuiltinLintDiagnostics::AbsPathWithModule(span) => {
+                    let (sugg, app) = match sess.source_map().span_to_snippet(span) {
+                        Ok(ref s) => {
+                            // FIXME(Manishearth) ideally the emitting code
+                            // can tell us whether or not this is global
+                            let opt_colon =
+                                if s.trim_start().starts_with("::") { "" } else { "::" };
+
+                            (format!("crate{}{}", opt_colon, s), Applicability::MachineApplicable)
+                        }
+                        Err(_) => ("crate::<path>".to_string(), Applicability::HasPlaceholders),
+                    };
+                    db.span_suggestion(span, "use `crate`", sugg, app);
+                }
+                BuiltinLintDiagnostics::ProcMacroDeriveResolutionFallback(span) => {
+                    db.span_label(
+                        span,
+                        "names from parent modules are not accessible without an explicit import",
+                    );
+                }
+                BuiltinLintDiagnostics::MacroExpandedMacroExportsAccessedByAbsolutePaths(
+                    span_def,
+                ) => {
+                    db.span_note(span_def, "the macro is defined here");
+                }
+                BuiltinLintDiagnostics::ElidedLifetimesInPaths(
+                    n,
+                    path_span,
+                    incl_angl_brckt,
+                    insertion_span,
+                    anon_lts,
+                ) => {
+                    add_elided_lifetime_in_path_suggestion(
+                        sess,
+                        &mut db,
+                        n,
+                        path_span,
+                        incl_angl_brckt,
+                        insertion_span,
+                        anon_lts,
+                    );
+                }
+                BuiltinLintDiagnostics::UnknownCrateTypes(span, note, sugg) => {
+                    db.span_suggestion(span, &note, sugg, Applicability::MaybeIncorrect);
+                }
+                BuiltinLintDiagnostics::UnusedImports(message, replaces) => {
+                    if !replaces.is_empty() {
+                        db.tool_only_multipart_suggestion(
+                            &message,
+                            replaces,
+                            Applicability::MachineApplicable,
+                        );
+                    }
+                }
+                BuiltinLintDiagnostics::RedundantImport(spans, ident) => {
+                    for (span, is_imported) in spans {
+                        let introduced = if is_imported { "imported" } else { "defined" };
+                        db.span_label(
+                            span,
+                            format!("the item `{}` is already {} here", ident, introduced),
+                        );
+                    }
+                }
+                BuiltinLintDiagnostics::DeprecatedMacro(suggestion, span) => {
+                    stability::deprecation_suggestion(&mut db, "macro", suggestion, span)
+                }
+                BuiltinLintDiagnostics::UnusedDocComment(span) => {
+                    db.span_label(span, "rustdoc does not generate documentation for macro invocations");
+                    db.help("to document an item produced by a macro, \
+                                  the macro must produce the documentation as part of its expansion");
+                }
+            }
+            // Rewrap `db`, and pass control to the user.
+            decorate(LintDiagnosticBuilder::new(db));
+        });
+    }
+
+    // FIXME: These methods should not take an Into<MultiSpan> -- instead, callers should need to
+    // set the span in their `decorate` function (preferably using set_span).
+    fn lookup<S: Into<MultiSpan>>(
+        &self,
+        lint: &'static Lint,
+        span: Option<S>,
+        decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
+    );
+
+    fn struct_span_lint<S: Into<MultiSpan>>(
+        &self,
+        lint: &'static Lint,
+        span: S,
+        decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
+    ) {
+        self.lookup(lint, Some(span), decorate);
+    }
+    /// Emit a lint at the appropriate level, with no associated span.
+    fn lint(&self, lint: &'static Lint, decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>)) {
+        self.lookup(lint, None as Option<Span>, decorate);
+    }
+}
+
+impl<'a> EarlyContext<'a> {
+    pub fn new(
+        sess: &'a Session,
+        lint_store: &'a LintStore,
+        krate: &'a ast::Crate,
+        buffered: LintBuffer,
+        warn_about_weird_lints: bool,
+    ) -> EarlyContext<'a> {
+        EarlyContext {
+            sess,
+            krate,
+            lint_store,
+            builder: LintLevelsBuilder::new(sess, warn_about_weird_lints, lint_store),
+            buffered,
+        }
+    }
+}
+
+impl LintContext for LateContext<'_> {
+    type PassObject = LateLintPassObject;
+
+    /// Gets the overall compiler `Session` object.
+    fn sess(&self) -> &Session {
+        &self.tcx.sess
+    }
+
+    fn lints(&self) -> &LintStore {
+        &*self.lint_store
+    }
+
+    fn lookup<S: Into<MultiSpan>>(
+        &self,
+        lint: &'static Lint,
+        span: Option<S>,
+        decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
+    ) {
+        let hir_id = self.last_node_with_lint_attrs;
+
+        match span {
+            Some(s) => self.tcx.struct_span_lint_hir(lint, hir_id, s, decorate),
+            None => self.tcx.struct_lint_node(lint, hir_id, decorate),
+        }
+    }
+}
+
+impl LintContext for EarlyContext<'_> {
+    type PassObject = EarlyLintPassObject;
+
+    /// Gets the overall compiler `Session` object.
+    fn sess(&self) -> &Session {
+        &self.sess
+    }
+
+    fn lints(&self) -> &LintStore {
+        &*self.lint_store
+    }
+
+    fn lookup<S: Into<MultiSpan>>(
+        &self,
+        lint: &'static Lint,
+        span: Option<S>,
+        decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
+    ) {
+        self.builder.struct_lint(lint, span.map(|s| s.into()), decorate)
+    }
+}
+
+impl<'tcx> LateContext<'tcx> {
+    /// Gets the type-checking results for the current body,
+    /// or `None` if outside a body.
+    pub fn maybe_typeck_results(&self) -> Option<&'tcx ty::TypeckResults<'tcx>> {
+        self.cached_typeck_results.get().or_else(|| {
+            self.enclosing_body.map(|body| {
+                let typeck_results = self.tcx.typeck_body(body);
+                self.cached_typeck_results.set(Some(typeck_results));
+                typeck_results
+            })
+        })
+    }
+
+    /// Gets the type-checking results for the current body.
+    /// As this will ICE if called outside bodies, only call when working with
+    /// `Expr` or `Pat` nodes (they are guaranteed to be found only in bodies).
+    #[track_caller]
+    pub fn typeck_results(&self) -> &'tcx ty::TypeckResults<'tcx> {
+        self.maybe_typeck_results().expect("`LateContext::typeck_results` called outside of body")
+    }
+
+    /// Returns the final resolution of a `QPath`, or `Res::Err` if unavailable.
+    /// Unlike `.typeck_results().qpath_res(qpath, id)`, this can be used even outside
+    /// bodies (e.g. for paths in `hir::Ty`), without any risk of ICE-ing.
+    pub fn qpath_res(&self, qpath: &hir::QPath<'_>, id: hir::HirId) -> Res {
+        match *qpath {
+            hir::QPath::Resolved(_, ref path) => path.res,
+            hir::QPath::TypeRelative(..) | hir::QPath::LangItem(..) => self
+                .maybe_typeck_results()
+                .and_then(|typeck_results| typeck_results.type_dependent_def(id))
+                .map_or(Res::Err, |(kind, def_id)| Res::Def(kind, def_id)),
+        }
+    }
+
+    pub fn current_lint_root(&self) -> hir::HirId {
+        self.last_node_with_lint_attrs
+    }
+
+    /// Check if a `DefId`'s path matches the given absolute type path usage.
+    ///
+    /// Anonymous scopes such as `extern` imports are matched with `kw::Invalid`;
+    /// inherent `impl` blocks are matched with the name of the type.
+    ///
+    /// # Examples
+    ///
+    /// ```rust,ignore (no context or def id available)
+    /// if cx.match_def_path(def_id, &[sym::core, sym::option, sym::Option]) {
+    ///     // The given `def_id` is that of an `Option` type
+    /// }
+    /// ```
+    pub fn match_def_path(&self, def_id: DefId, path: &[Symbol]) -> bool {
+        let names = self.get_def_path(def_id);
+
+        names.len() == path.len() && names.into_iter().zip(path.iter()).all(|(a, &b)| a == b)
+    }
+
+    /// Gets the absolute path of `def_id` as a vector of `Symbol`.
+    ///
+    /// # Examples
+    ///
+    /// ```rust,ignore (no context or def id available)
+    /// let def_path = cx.get_def_path(def_id);
+    /// if let &[sym::core, sym::option, sym::Option] = &def_path[..] {
+    ///     // The given `def_id` is that of an `Option` type
+    /// }
+    /// ```
+    pub fn get_def_path(&self, def_id: DefId) -> Vec<Symbol> {
+        pub struct AbsolutePathPrinter<'tcx> {
+            pub tcx: TyCtxt<'tcx>,
+        }
+
+        impl<'tcx> Printer<'tcx> for AbsolutePathPrinter<'tcx> {
+            type Error = !;
+
+            type Path = Vec<Symbol>;
+            type Region = ();
+            type Type = ();
+            type DynExistential = ();
+            type Const = ();
+
+            fn tcx(&self) -> TyCtxt<'tcx> {
+                self.tcx
+            }
+
+            fn print_region(self, _region: ty::Region<'_>) -> Result<Self::Region, Self::Error> {
+                Ok(())
+            }
+
+            fn print_type(self, _ty: Ty<'tcx>) -> Result<Self::Type, Self::Error> {
+                Ok(())
+            }
+
+            fn print_dyn_existential(
+                self,
+                _predicates: &'tcx ty::List<ty::ExistentialPredicate<'tcx>>,
+            ) -> Result<Self::DynExistential, Self::Error> {
+                Ok(())
+            }
+
+            fn print_const(self, _ct: &'tcx ty::Const<'tcx>) -> Result<Self::Const, Self::Error> {
+                Ok(())
+            }
+
+            fn path_crate(self, cnum: CrateNum) -> Result<Self::Path, Self::Error> {
+                Ok(vec![self.tcx.original_crate_name(cnum)])
+            }
+
+            fn path_qualified(
+                self,
+                self_ty: Ty<'tcx>,
+                trait_ref: Option<ty::TraitRef<'tcx>>,
+            ) -> Result<Self::Path, Self::Error> {
+                if trait_ref.is_none() {
+                    if let ty::Adt(def, substs) = self_ty.kind {
+                        return self.print_def_path(def.did, substs);
+                    }
+                }
+
+                // This shouldn't ever be needed, but just in case:
+                Ok(vec![match trait_ref {
+                    Some(trait_ref) => Symbol::intern(&format!("{:?}", trait_ref)),
+                    None => Symbol::intern(&format!("<{}>", self_ty)),
+                }])
+            }
+
+            fn path_append_impl(
+                self,
+                print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
+                _disambiguated_data: &DisambiguatedDefPathData,
+                self_ty: Ty<'tcx>,
+                trait_ref: Option<ty::TraitRef<'tcx>>,
+            ) -> Result<Self::Path, Self::Error> {
+                let mut path = print_prefix(self)?;
+
+                // This shouldn't ever be needed, but just in case:
+                path.push(match trait_ref {
+                    Some(trait_ref) => Symbol::intern(&format!(
+                        "<impl {} for {}>",
+                        trait_ref.print_only_trait_path(),
+                        self_ty
+                    )),
+                    None => Symbol::intern(&format!("<impl {}>", self_ty)),
+                });
+
+                Ok(path)
+            }
+
+            fn path_append(
+                self,
+                print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
+                disambiguated_data: &DisambiguatedDefPathData,
+            ) -> Result<Self::Path, Self::Error> {
+                let mut path = print_prefix(self)?;
+
+                // Skip `::{{constructor}}` on tuple/unit structs.
+                if let DefPathData::Ctor = disambiguated_data.data {
+                    return Ok(path);
+                }
+
+                path.push(disambiguated_data.data.as_symbol());
+                Ok(path)
+            }
+
+            fn path_generic_args(
+                self,
+                print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
+                _args: &[GenericArg<'tcx>],
+            ) -> Result<Self::Path, Self::Error> {
+                print_prefix(self)
+            }
+        }
+
+        AbsolutePathPrinter { tcx: self.tcx }.print_def_path(def_id, &[]).unwrap()
+    }
+}
+
+impl<'tcx> LayoutOf for LateContext<'tcx> {
+    type Ty = Ty<'tcx>;
+    type TyAndLayout = Result<TyAndLayout<'tcx>, LayoutError<'tcx>>;
+
+    fn layout_of(&self, ty: Ty<'tcx>) -> Self::TyAndLayout {
+        self.tcx.layout_of(self.param_env.and(ty))
+    }
+}

compiler/rustc_lint/src/early.rs

@@ -0,0 +1,381 @@
+//! Implementation of lint checking.
+//!
+//! The lint checking is mostly consolidated into one pass which runs
+//! after all other analyses. Throughout compilation, lint warnings
+//! can be added via the `add_lint` method on the Session structure. This
+//! requires a span and an ID of the node that the lint is being added to. The
+//! lint isn't actually emitted at that time because it is unknown what the
+//! actual lint level at that location is.
+//!
+//! To actually emit lint warnings/errors, a separate pass is used.
+//! A context keeps track of the current state of all lint levels.
+//! Upon entering a node of the ast which can modify the lint settings, the
+//! previous lint state is pushed onto a stack and the ast is then recursed
+//! upon. As the ast is traversed, this keeps track of the current lint level
+//! for all lint attributes.
+
+use crate::context::{EarlyContext, LintContext, LintStore};
+use crate::passes::{EarlyLintPass, EarlyLintPassObject};
+use rustc_ast as ast;
+use rustc_ast::visit as ast_visit;
+use rustc_session::lint::{BufferedEarlyLint, LintBuffer, LintPass};
+use rustc_session::Session;
+use rustc_span::symbol::Ident;
+use rustc_span::Span;
+
+use std::slice;
+use tracing::debug;
+
+macro_rules! run_early_pass { ($cx:expr, $f:ident, $($args:expr),*) => ({
+    $cx.pass.$f(&$cx.context, $($args),*);
+}) }
+
+struct EarlyContextAndPass<'a, T: EarlyLintPass> {
+    context: EarlyContext<'a>,
+    pass: T,
+}
+
+impl<'a, T: EarlyLintPass> EarlyContextAndPass<'a, T> {
+    fn check_id(&mut self, id: ast::NodeId) {
+        for early_lint in self.context.buffered.take(id) {
+            let BufferedEarlyLint { span, msg, node_id: _, lint_id, diagnostic } = early_lint;
+            self.context.lookup_with_diagnostics(
+                lint_id.lint,
+                Some(span),
+                |lint| lint.build(&msg).emit(),
+                diagnostic,
+            );
+        }
+    }
+
+    /// Merge the lints specified by any lint attributes into the
+    /// current lint context, call the provided function, then reset the
+    /// lints in effect to their previous state.
+    fn with_lint_attrs<F>(&mut self, id: ast::NodeId, attrs: &'a [ast::Attribute], f: F)
+    where
+        F: FnOnce(&mut Self),
+    {
+        let is_crate_node = id == ast::CRATE_NODE_ID;
+        let push = self.context.builder.push(attrs, &self.context.lint_store, is_crate_node);
+        self.check_id(id);
+        self.enter_attrs(attrs);
+        f(self);
+        self.exit_attrs(attrs);
+        self.context.builder.pop(push);
+    }
+
+    fn enter_attrs(&mut self, attrs: &'a [ast::Attribute]) {
+        debug!("early context: enter_attrs({:?})", attrs);
+        run_early_pass!(self, enter_lint_attrs, attrs);
+    }
+
+    fn exit_attrs(&mut self, attrs: &'a [ast::Attribute]) {
+        debug!("early context: exit_attrs({:?})", attrs);
+        run_early_pass!(self, exit_lint_attrs, attrs);
+    }
+}
+
+impl<'a, T: EarlyLintPass> ast_visit::Visitor<'a> for EarlyContextAndPass<'a, T> {
+    fn visit_param(&mut self, param: &'a ast::Param) {
+        self.with_lint_attrs(param.id, &param.attrs, |cx| {
+            run_early_pass!(cx, check_param, param);
+            ast_visit::walk_param(cx, param);
+        });
+    }
+
+    fn visit_item(&mut self, it: &'a ast::Item) {
+        self.with_lint_attrs(it.id, &it.attrs, |cx| {
+            run_early_pass!(cx, check_item, it);
+            ast_visit::walk_item(cx, it);
+            run_early_pass!(cx, check_item_post, it);
+        })
+    }
+
+    fn visit_foreign_item(&mut self, it: &'a ast::ForeignItem) {
+        self.with_lint_attrs(it.id, &it.attrs, |cx| {
+            run_early_pass!(cx, check_foreign_item, it);
+            ast_visit::walk_foreign_item(cx, it);
+            run_early_pass!(cx, check_foreign_item_post, it);
+        })
+    }
+
+    fn visit_pat(&mut self, p: &'a ast::Pat) {
+        run_early_pass!(self, check_pat, p);
+        self.check_id(p.id);
+        ast_visit::walk_pat(self, p);
+        run_early_pass!(self, check_pat_post, p);
+    }
+
+    fn visit_anon_const(&mut self, c: &'a ast::AnonConst) {
+        run_early_pass!(self, check_anon_const, c);
+        ast_visit::walk_anon_const(self, c);
+    }
+
+    fn visit_expr(&mut self, e: &'a ast::Expr) {
+        self.with_lint_attrs(e.id, &e.attrs, |cx| {
+            run_early_pass!(cx, check_expr, e);
+            ast_visit::walk_expr(cx, e);
+        })
+    }
+
+    fn visit_stmt(&mut self, s: &'a ast::Stmt) {
+        run_early_pass!(self, check_stmt, s);
+        self.check_id(s.id);
+        ast_visit::walk_stmt(self, s);
+    }
+
+    fn visit_fn(&mut self, fk: ast_visit::FnKind<'a>, span: Span, id: ast::NodeId) {
+        run_early_pass!(self, check_fn, fk, span, id);
+        self.check_id(id);
+        ast_visit::walk_fn(self, fk, span);
+        run_early_pass!(self, check_fn_post, fk, span, id);
+    }
+
+    fn visit_variant_data(&mut self, s: &'a ast::VariantData) {
+        run_early_pass!(self, check_struct_def, s);
+        if let Some(ctor_hir_id) = s.ctor_id() {
+            self.check_id(ctor_hir_id);
+        }
+        ast_visit::walk_struct_def(self, s);
+        run_early_pass!(self, check_struct_def_post, s);
+    }
+
+    fn visit_struct_field(&mut self, s: &'a ast::StructField) {
+        self.with_lint_attrs(s.id, &s.attrs, |cx| {
+            run_early_pass!(cx, check_struct_field, s);
+            ast_visit::walk_struct_field(cx, s);
+        })
+    }
+
+    fn visit_variant(&mut self, v: &'a ast::Variant) {
+        self.with_lint_attrs(v.id, &v.attrs, |cx| {
+            run_early_pass!(cx, check_variant, v);
+            ast_visit::walk_variant(cx, v);
+            run_early_pass!(cx, check_variant_post, v);
+        })
+    }
+
+    fn visit_ty(&mut self, t: &'a ast::Ty) {
+        run_early_pass!(self, check_ty, t);
+        self.check_id(t.id);
+        ast_visit::walk_ty(self, t);
+    }
+
+    fn visit_ident(&mut self, ident: Ident) {
+        run_early_pass!(self, check_ident, ident);
+    }
+
+    fn visit_mod(&mut self, m: &'a ast::Mod, s: Span, _a: &[ast::Attribute], n: ast::NodeId) {
+        run_early_pass!(self, check_mod, m, s, n);
+        self.check_id(n);
+        ast_visit::walk_mod(self, m);
+        run_early_pass!(self, check_mod_post, m, s, n);
+    }
+
+    fn visit_local(&mut self, l: &'a ast::Local) {
+        self.with_lint_attrs(l.id, &l.attrs, |cx| {
+            run_early_pass!(cx, check_local, l);
+            ast_visit::walk_local(cx, l);
+        })
+    }
+
+    fn visit_block(&mut self, b: &'a ast::Block) {
+        run_early_pass!(self, check_block, b);
+        self.check_id(b.id);
+        ast_visit::walk_block(self, b);
+        run_early_pass!(self, check_block_post, b);
+    }
+
+    fn visit_arm(&mut self, a: &'a ast::Arm) {
+        run_early_pass!(self, check_arm, a);
+        ast_visit::walk_arm(self, a);
+    }
+
+    fn visit_expr_post(&mut self, e: &'a ast::Expr) {
+        run_early_pass!(self, check_expr_post, e);
+    }
+
+    fn visit_generic_param(&mut self, param: &'a ast::GenericParam) {
+        run_early_pass!(self, check_generic_param, param);
+        ast_visit::walk_generic_param(self, param);
+    }
+
+    fn visit_generics(&mut self, g: &'a ast::Generics) {
+        run_early_pass!(self, check_generics, g);
+        ast_visit::walk_generics(self, g);
+    }
+
+    fn visit_where_predicate(&mut self, p: &'a ast::WherePredicate) {
+        run_early_pass!(self, check_where_predicate, p);
+        ast_visit::walk_where_predicate(self, p);
+    }
+
+    fn visit_poly_trait_ref(&mut self, t: &'a ast::PolyTraitRef, m: &'a ast::TraitBoundModifier) {
+        run_early_pass!(self, check_poly_trait_ref, t, m);
+        ast_visit::walk_poly_trait_ref(self, t, m);
+    }
+
+    fn visit_assoc_item(&mut self, item: &'a ast::AssocItem, ctxt: ast_visit::AssocCtxt) {
+        self.with_lint_attrs(item.id, &item.attrs, |cx| match ctxt {
+            ast_visit::AssocCtxt::Trait => {
+                run_early_pass!(cx, check_trait_item, item);
+                ast_visit::walk_assoc_item(cx, item, ctxt);
+                run_early_pass!(cx, check_trait_item_post, item);
+            }
+            ast_visit::AssocCtxt::Impl => {
+                run_early_pass!(cx, check_impl_item, item);
+                ast_visit::walk_assoc_item(cx, item, ctxt);
+                run_early_pass!(cx, check_impl_item_post, item);
+            }
+        });
+    }
+
+    fn visit_lifetime(&mut self, lt: &'a ast::Lifetime) {
+        run_early_pass!(self, check_lifetime, lt);
+        self.check_id(lt.id);
+    }
+
+    fn visit_path(&mut self, p: &'a ast::Path, id: ast::NodeId) {
+        run_early_pass!(self, check_path, p, id);
+        self.check_id(id);
+        ast_visit::walk_path(self, p);
+    }
+
+    fn visit_attribute(&mut self, attr: &'a ast::Attribute) {
+        run_early_pass!(self, check_attribute, attr);
+    }
+
+    fn visit_mac_def(&mut self, mac: &'a ast::MacroDef, id: ast::NodeId) {
+        run_early_pass!(self, check_mac_def, mac, id);
+        self.check_id(id);
+    }
+
+    fn visit_mac(&mut self, mac: &'a ast::MacCall) {
+        // FIXME(#54110): So, this setup isn't really right. I think
+        // that (a) the librustc_ast visitor ought to be doing this as
+        // part of `walk_mac`, and (b) we should be calling
+        // `visit_path`, *but* that would require a `NodeId`, and I
+        // want to get #53686 fixed quickly. -nmatsakis
+        ast_visit::walk_path(self, &mac.path);
+
+        run_early_pass!(self, check_mac, mac);
+    }
+}
+
+struct EarlyLintPassObjects<'a> {
+    lints: &'a mut [EarlyLintPassObject],
+}
+
+#[allow(rustc::lint_pass_impl_without_macro)]
+impl LintPass for EarlyLintPassObjects<'_> {
+    fn name(&self) -> &'static str {
+        panic!()
+    }
+}
+
+macro_rules! expand_early_lint_pass_impl_methods {
+    ([$($(#[$attr:meta])* fn $name:ident($($param:ident: $arg:ty),*);)*]) => (
+        $(fn $name(&mut self, context: &EarlyContext<'_>, $($param: $arg),*) {
+            for obj in self.lints.iter_mut() {
+                obj.$name(context, $($param),*);
+            }
+        })*
+    )
+}
+
+macro_rules! early_lint_pass_impl {
+    ([], [$($methods:tt)*]) => (
+        impl EarlyLintPass for EarlyLintPassObjects<'_> {
+            expand_early_lint_pass_impl_methods!([$($methods)*]);
+        }
+    )
+}
+
+crate::early_lint_methods!(early_lint_pass_impl, []);
+
+fn early_lint_crate<T: EarlyLintPass>(
+    sess: &Session,
+    lint_store: &LintStore,
+    krate: &ast::Crate,
+    pass: T,
+    buffered: LintBuffer,
+    warn_about_weird_lints: bool,
+) -> LintBuffer {
+    let mut cx = EarlyContextAndPass {
+        context: EarlyContext::new(sess, lint_store, krate, buffered, warn_about_weird_lints),
+        pass,
+    };
+
+    // Visit the whole crate.
+    cx.with_lint_attrs(ast::CRATE_NODE_ID, &krate.attrs, |cx| {
+        // since the root module isn't visited as an item (because it isn't an
+        // item), warn for it here.
+        run_early_pass!(cx, check_crate, krate);
+
+        ast_visit::walk_crate(cx, krate);
+
+        run_early_pass!(cx, check_crate_post, krate);
+    });
+    cx.context.buffered
+}
+
+pub fn check_ast_crate<T: EarlyLintPass>(
+    sess: &Session,
+    lint_store: &LintStore,
+    krate: &ast::Crate,
+    pre_expansion: bool,
+    lint_buffer: Option<LintBuffer>,
+    builtin_lints: T,
+) {
+    let passes =
+        if pre_expansion { &lint_store.pre_expansion_passes } else { &lint_store.early_passes };
+    let mut passes: Vec<_> = passes.iter().map(|p| (p)()).collect();
+    let mut buffered = lint_buffer.unwrap_or_default();
+
+    if !sess.opts.debugging_opts.no_interleave_lints {
+        buffered =
+            early_lint_crate(sess, lint_store, krate, builtin_lints, buffered, pre_expansion);
+
+        if !passes.is_empty() {
+            buffered = early_lint_crate(
+                sess,
+                lint_store,
+                krate,
+                EarlyLintPassObjects { lints: &mut passes[..] },
+                buffered,
+                pre_expansion,
+            );
+        }
+    } else {
+        for pass in &mut passes {
+            buffered =
+                sess.prof.extra_verbose_generic_activity("run_lint", pass.name()).run(|| {
+                    early_lint_crate(
+                        sess,
+                        lint_store,
+                        krate,
+                        EarlyLintPassObjects { lints: slice::from_mut(pass) },
+                        buffered,
+                        pre_expansion,
+                    )
+                });
+        }
+    }
+
+    // All of the buffered lints should have been emitted at this point.
+    // If not, that means that we somehow buffered a lint for a node id
+    // that was not lint-checked (perhaps it doesn't exist?). This is a bug.
+    //
+    // Rustdoc runs everybody-loops before the early lints and removes
+    // function bodies, so it's totally possible for linted
+    // node ids to not exist (e.g., macros defined within functions for the
+    // unused_macro lint) anymore. So we only run this check
+    // when we're not in rustdoc mode. (see issue #47639)
+    if !sess.opts.actually_rustdoc {
+        for (_id, lints) in buffered.map {
+            for early_lint in lints {
+                sess.delay_span_bug(early_lint.span, "failed to process buffered lint here");
+            }
+        }
+    }
+}

compiler/rustc_lint/src/internal.rs

@@ -0,0 +1,247 @@
+//! Some lints that are only useful in the compiler or crates that use compiler internals, such as
+//! Clippy.
+
+use crate::{EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext};
+use rustc_ast::{Item, ItemKind};
+use rustc_data_structures::fx::FxHashMap;
+use rustc_errors::Applicability;
+use rustc_hir::{GenericArg, HirId, MutTy, Mutability, Path, PathSegment, QPath, Ty, TyKind};
+use rustc_session::{declare_lint_pass, declare_tool_lint, impl_lint_pass};
+use rustc_span::hygiene::{ExpnKind, MacroKind};
+use rustc_span::symbol::{sym, Ident, Symbol};
+
+declare_tool_lint! {
+    pub rustc::DEFAULT_HASH_TYPES,
+    Allow,
+    "forbid HashMap and HashSet and suggest the FxHash* variants",
+    report_in_external_macro: true
+}
+
+pub struct DefaultHashTypes {
+    map: FxHashMap<Symbol, Symbol>,
+}
+
+impl DefaultHashTypes {
+    // we are allowed to use `HashMap` and `HashSet` as identifiers for implementing the lint itself
+    #[allow(rustc::default_hash_types)]
+    pub fn new() -> Self {
+        let mut map = FxHashMap::default();
+        map.insert(sym::HashMap, sym::FxHashMap);
+        map.insert(sym::HashSet, sym::FxHashSet);
+        Self { map }
+    }
+}
+
+impl_lint_pass!(DefaultHashTypes => [DEFAULT_HASH_TYPES]);
+
+impl EarlyLintPass for DefaultHashTypes {
+    fn check_ident(&mut self, cx: &EarlyContext<'_>, ident: Ident) {
+        if let Some(replace) = self.map.get(&ident.name) {
+            cx.struct_span_lint(DEFAULT_HASH_TYPES, ident.span, |lint| {
+                // FIXME: We can avoid a copy here. Would require us to take String instead of &str.
+                let msg = format!("Prefer {} over {}, it has better performance", replace, ident);
+                lint.build(&msg)
+                    .span_suggestion(
+                        ident.span,
+                        "use",
+                        replace.to_string(),
+                        Applicability::MaybeIncorrect, // FxHashMap, ... needs another import
+                    )
+                    .note(&format!(
+                        "a `use rustc_data_structures::fx::{}` may be necessary",
+                        replace
+                    ))
+                    .emit();
+            });
+        }
+    }
+}
+
+declare_tool_lint! {
+    pub rustc::USAGE_OF_TY_TYKIND,
+    Allow,
+    "usage of `ty::TyKind` outside of the `ty::sty` module",
+    report_in_external_macro: true
+}
+
+declare_tool_lint! {
+    pub rustc::TY_PASS_BY_REFERENCE,
+    Allow,
+    "passing `Ty` or `TyCtxt` by reference",
+    report_in_external_macro: true
+}
+
+declare_tool_lint! {
+    pub rustc::USAGE_OF_QUALIFIED_TY,
+    Allow,
+    "using `ty::{Ty,TyCtxt}` instead of importing it",
+    report_in_external_macro: true
+}
+
+declare_lint_pass!(TyTyKind => [
+    USAGE_OF_TY_TYKIND,
+    TY_PASS_BY_REFERENCE,
+    USAGE_OF_QUALIFIED_TY,
+]);
+
+impl<'tcx> LateLintPass<'tcx> for TyTyKind {
+    fn check_path(&mut self, cx: &LateContext<'_>, path: &'tcx Path<'tcx>, _: HirId) {
+        let segments = path.segments.iter().rev().skip(1).rev();
+
+        if let Some(last) = segments.last() {
+            let span = path.span.with_hi(last.ident.span.hi());
+            if lint_ty_kind_usage(cx, last) {
+                cx.struct_span_lint(USAGE_OF_TY_TYKIND, span, |lint| {
+                    lint.build("usage of `ty::TyKind::<kind>`")
+                        .span_suggestion(
+                            span,
+                            "try using ty::<kind> directly",
+                            "ty".to_string(),
+                            Applicability::MaybeIncorrect, // ty maybe needs an import
+                        )
+                        .emit();
+                })
+            }
+        }
+    }
+
+    fn check_ty(&mut self, cx: &LateContext<'_>, ty: &'tcx Ty<'tcx>) {
+        match &ty.kind {
+            TyKind::Path(qpath) => {
+                if let QPath::Resolved(_, path) = qpath {
+                    if let Some(last) = path.segments.iter().last() {
+                        if lint_ty_kind_usage(cx, last) {
+                            cx.struct_span_lint(USAGE_OF_TY_TYKIND, path.span, |lint| {
+                                lint.build("usage of `ty::TyKind`")
+                                    .help("try using `Ty` instead")
+                                    .emit();
+                            })
+                        } else {
+                            if ty.span.from_expansion() {
+                                return;
+                            }
+                            if let Some(t) = is_ty_or_ty_ctxt(cx, ty) {
+                                if path.segments.len() > 1 {
+                                    cx.struct_span_lint(USAGE_OF_QUALIFIED_TY, path.span, |lint| {
+                                        lint.build(&format!("usage of qualified `ty::{}`", t))
+                                            .span_suggestion(
+                                                path.span,
+                                                "try using it unqualified",
+                                                t,
+                                                // The import probably needs to be changed
+                                                Applicability::MaybeIncorrect,
+                                            )
+                                            .emit();
+                                    })
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+            TyKind::Rptr(_, MutTy { ty: inner_ty, mutbl: Mutability::Not }) => {
+                if let Some(impl_did) = cx.tcx.impl_of_method(ty.hir_id.owner.to_def_id()) {
+                    if cx.tcx.impl_trait_ref(impl_did).is_some() {
+                        return;
+                    }
+                }
+                if let Some(t) = is_ty_or_ty_ctxt(cx, &inner_ty) {
+                    cx.struct_span_lint(TY_PASS_BY_REFERENCE, ty.span, |lint| {
+                        lint.build(&format!("passing `{}` by reference", t))
+                            .span_suggestion(
+                                ty.span,
+                                "try passing by value",
+                                t,
+                                // Changing type of function argument
+                                Applicability::MaybeIncorrect,
+                            )
+                            .emit();
+                    })
+                }
+            }
+            _ => {}
+        }
+    }
+}
+
+fn lint_ty_kind_usage(cx: &LateContext<'_>, segment: &PathSegment<'_>) -> bool {
+    if let Some(res) = segment.res {
+        if let Some(did) = res.opt_def_id() {
+            return cx.tcx.is_diagnostic_item(sym::TyKind, did);
+        }
+    }
+
+    false
+}
+
+fn is_ty_or_ty_ctxt(cx: &LateContext<'_>, ty: &Ty<'_>) -> Option<String> {
+    if let TyKind::Path(qpath) = &ty.kind {
+        if let QPath::Resolved(_, path) = qpath {
+            let did = path.res.opt_def_id()?;
+            if cx.tcx.is_diagnostic_item(sym::Ty, did) {
+                return Some(format!("Ty{}", gen_args(path.segments.last().unwrap())));
+            } else if cx.tcx.is_diagnostic_item(sym::TyCtxt, did) {
+                return Some(format!("TyCtxt{}", gen_args(path.segments.last().unwrap())));
+            }
+        }
+    }
+
+    None
+}
+
+fn gen_args(segment: &PathSegment<'_>) -> String {
+    if let Some(args) = &segment.args {
+        let lifetimes = args
+            .args
+            .iter()
+            .filter_map(|arg| {
+                if let GenericArg::Lifetime(lt) = arg {
+                    Some(lt.name.ident().to_string())
+                } else {
+                    None
+                }
+            })
+            .collect::<Vec<_>>();
+
+        if !lifetimes.is_empty() {
+            return format!("<{}>", lifetimes.join(", "));
+        }
+    }
+
+    String::new()
+}
+
+declare_tool_lint! {
+    pub rustc::LINT_PASS_IMPL_WITHOUT_MACRO,
+    Allow,
+    "`impl LintPass` without the `declare_lint_pass!` or `impl_lint_pass!` macros"
+}
+
+declare_lint_pass!(LintPassImpl => [LINT_PASS_IMPL_WITHOUT_MACRO]);
+
+impl EarlyLintPass for LintPassImpl {
+    fn check_item(&mut self, cx: &EarlyContext<'_>, item: &Item) {
+        if let ItemKind::Impl { of_trait: Some(lint_pass), .. } = &item.kind {
+            if let Some(last) = lint_pass.path.segments.last() {
+                if last.ident.name == sym::LintPass {
+                    let expn_data = lint_pass.path.span.ctxt().outer_expn_data();
+                    let call_site = expn_data.call_site;
+                    if expn_data.kind != ExpnKind::Macro(MacroKind::Bang, sym::impl_lint_pass)
+                        && call_site.ctxt().outer_expn_data().kind
+                            != ExpnKind::Macro(MacroKind::Bang, sym::declare_lint_pass)
+                    {
+                        cx.struct_span_lint(
+                            LINT_PASS_IMPL_WITHOUT_MACRO,
+                            lint_pass.path.span,
+                            |lint| {
+                                lint.build("implementing `LintPass` by hand")
+                                    .help("try using `declare_lint_pass!` or `impl_lint_pass!` instead")
+                                    .emit();
+                            },
+                        )
+                    }
+                }
+            }
+        }
+    }
+}

compiler/rustc_lint/src/late.rs

@@ -0,0 +1,499 @@
+//! Implementation of lint checking.
+//!
+//! The lint checking is mostly consolidated into one pass which runs
+//! after all other analyses. Throughout compilation, lint warnings
+//! can be added via the `add_lint` method on the Session structure. This
+//! requires a span and an ID of the node that the lint is being added to. The
+//! lint isn't actually emitted at that time because it is unknown what the
+//! actual lint level at that location is.
+//!
+//! To actually emit lint warnings/errors, a separate pass is used.
+//! A context keeps track of the current state of all lint levels.
+//! Upon entering a node of the ast which can modify the lint settings, the
+//! previous lint state is pushed onto a stack and the ast is then recursed
+//! upon. As the ast is traversed, this keeps track of the current lint level
+//! for all lint attributes.
+
+use crate::{passes::LateLintPassObject, LateContext, LateLintPass, LintStore};
+use rustc_ast as ast;
+use rustc_ast::walk_list;
+use rustc_data_structures::sync::{join, par_iter, ParallelIterator};
+use rustc_hir as hir;
+use rustc_hir::def_id::{LocalDefId, LOCAL_CRATE};
+use rustc_hir::intravisit as hir_visit;
+use rustc_hir::intravisit::Visitor;
+use rustc_middle::hir::map::Map;
+use rustc_middle::ty::{self, TyCtxt};
+use rustc_session::lint::LintPass;
+use rustc_span::symbol::Symbol;
+use rustc_span::Span;
+
+use std::any::Any;
+use std::cell::Cell;
+use std::slice;
+use tracing::debug;
+
+/// Extract the `LintStore` from the query context.
+/// This function exists because we've erased `LintStore` as `dyn Any` in the context.
+crate fn unerased_lint_store(tcx: TyCtxt<'_>) -> &LintStore {
+    let store: &dyn Any = &*tcx.lint_store;
+    store.downcast_ref().unwrap()
+}
+
+macro_rules! lint_callback { ($cx:expr, $f:ident, $($args:expr),*) => ({
+    $cx.pass.$f(&$cx.context, $($args),*);
+}) }
+
+struct LateContextAndPass<'tcx, T: LateLintPass<'tcx>> {
+    context: LateContext<'tcx>,
+    pass: T,
+}
+
+impl<'tcx, T: LateLintPass<'tcx>> LateContextAndPass<'tcx, T> {
+    /// Merge the lints specified by any lint attributes into the
+    /// current lint context, call the provided function, then reset the
+    /// lints in effect to their previous state.
+    fn with_lint_attrs<F>(&mut self, id: hir::HirId, attrs: &'tcx [ast::Attribute], f: F)
+    where
+        F: FnOnce(&mut Self),
+    {
+        let prev = self.context.last_node_with_lint_attrs;
+        self.context.last_node_with_lint_attrs = id;
+        self.enter_attrs(attrs);
+        f(self);
+        self.exit_attrs(attrs);
+        self.context.last_node_with_lint_attrs = prev;
+    }
+
+    fn with_param_env<F>(&mut self, id: hir::HirId, f: F)
+    where
+        F: FnOnce(&mut Self),
+    {
+        let old_param_env = self.context.param_env;
+        self.context.param_env =
+            self.context.tcx.param_env(self.context.tcx.hir().local_def_id(id));
+        f(self);
+        self.context.param_env = old_param_env;
+    }
+
+    fn process_mod(&mut self, m: &'tcx hir::Mod<'tcx>, s: Span, n: hir::HirId) {
+        lint_callback!(self, check_mod, m, s, n);
+        hir_visit::walk_mod(self, m, n);
+        lint_callback!(self, check_mod_post, m, s, n);
+    }
+
+    fn enter_attrs(&mut self, attrs: &'tcx [ast::Attribute]) {
+        debug!("late context: enter_attrs({:?})", attrs);
+        lint_callback!(self, enter_lint_attrs, attrs);
+    }
+
+    fn exit_attrs(&mut self, attrs: &'tcx [ast::Attribute]) {
+        debug!("late context: exit_attrs({:?})", attrs);
+        lint_callback!(self, exit_lint_attrs, attrs);
+    }
+}
+
+impl<'tcx, T: LateLintPass<'tcx>> hir_visit::Visitor<'tcx> for LateContextAndPass<'tcx, T> {
+    type Map = Map<'tcx>;
+
+    /// Because lints are scoped lexically, we want to walk nested
+    /// items in the context of the outer item, so enable
+    /// deep-walking.
+    fn nested_visit_map(&mut self) -> hir_visit::NestedVisitorMap<Self::Map> {
+        hir_visit::NestedVisitorMap::All(self.context.tcx.hir())
+    }
+
+    fn visit_nested_body(&mut self, body_id: hir::BodyId) {
+        let old_enclosing_body = self.context.enclosing_body.replace(body_id);
+        let old_cached_typeck_results = self.context.cached_typeck_results.get();
+
+        // HACK(eddyb) avoid trashing `cached_typeck_results` when we're
+        // nested in `visit_fn`, which may have already resulted in them
+        // being queried.
+        if old_enclosing_body != Some(body_id) {
+            self.context.cached_typeck_results.set(None);
+        }
+
+        let body = self.context.tcx.hir().body(body_id);
+        self.visit_body(body);
+        self.context.enclosing_body = old_enclosing_body;
+
+        // See HACK comment above.
+        if old_enclosing_body != Some(body_id) {
+            self.context.cached_typeck_results.set(old_cached_typeck_results);
+        }
+    }
+
+    fn visit_param(&mut self, param: &'tcx hir::Param<'tcx>) {
+        self.with_lint_attrs(param.hir_id, &param.attrs, |cx| {
+            lint_callback!(cx, check_param, param);
+            hir_visit::walk_param(cx, param);
+        });
+    }
+
+    fn visit_body(&mut self, body: &'tcx hir::Body<'tcx>) {
+        lint_callback!(self, check_body, body);
+        hir_visit::walk_body(self, body);
+        lint_callback!(self, check_body_post, body);
+    }
+
+    fn visit_item(&mut self, it: &'tcx hir::Item<'tcx>) {
+        let generics = self.context.generics.take();
+        self.context.generics = it.kind.generics();
+        self.with_lint_attrs(it.hir_id, &it.attrs, |cx| {
+            cx.with_param_env(it.hir_id, |cx| {
+                lint_callback!(cx, check_item, it);
+                hir_visit::walk_item(cx, it);
+                lint_callback!(cx, check_item_post, it);
+            });
+        });
+        self.context.generics = generics;
+    }
+
+    fn visit_foreign_item(&mut self, it: &'tcx hir::ForeignItem<'tcx>) {
+        self.with_lint_attrs(it.hir_id, &it.attrs, |cx| {
+            cx.with_param_env(it.hir_id, |cx| {
+                lint_callback!(cx, check_foreign_item, it);
+                hir_visit::walk_foreign_item(cx, it);
+                lint_callback!(cx, check_foreign_item_post, it);
+            });
+        })
+    }
+
+    fn visit_pat(&mut self, p: &'tcx hir::Pat<'tcx>) {
+        lint_callback!(self, check_pat, p);
+        hir_visit::walk_pat(self, p);
+    }
+
+    fn visit_expr(&mut self, e: &'tcx hir::Expr<'tcx>) {
+        self.with_lint_attrs(e.hir_id, &e.attrs, |cx| {
+            lint_callback!(cx, check_expr, e);
+            hir_visit::walk_expr(cx, e);
+            lint_callback!(cx, check_expr_post, e);
+        })
+    }
+
+    fn visit_stmt(&mut self, s: &'tcx hir::Stmt<'tcx>) {
+        // statement attributes are actually just attributes on one of
+        // - item
+        // - local
+        // - expression
+        // so we keep track of lint levels there
+        lint_callback!(self, check_stmt, s);
+        hir_visit::walk_stmt(self, s);
+    }
+
+    fn visit_fn(
+        &mut self,
+        fk: hir_visit::FnKind<'tcx>,
+        decl: &'tcx hir::FnDecl<'tcx>,
+        body_id: hir::BodyId,
+        span: Span,
+        id: hir::HirId,
+    ) {
+        // Wrap in typeck results here, not just in visit_nested_body,
+        // in order for `check_fn` to be able to use them.
+        let old_enclosing_body = self.context.enclosing_body.replace(body_id);
+        let old_cached_typeck_results = self.context.cached_typeck_results.take();
+        let body = self.context.tcx.hir().body(body_id);
+        lint_callback!(self, check_fn, fk, decl, body, span, id);
+        hir_visit::walk_fn(self, fk, decl, body_id, span, id);
+        lint_callback!(self, check_fn_post, fk, decl, body, span, id);
+        self.context.enclosing_body = old_enclosing_body;
+        self.context.cached_typeck_results.set(old_cached_typeck_results);
+    }
+
+    fn visit_variant_data(
+        &mut self,
+        s: &'tcx hir::VariantData<'tcx>,
+        _: Symbol,
+        _: &'tcx hir::Generics<'tcx>,
+        _: hir::HirId,
+        _: Span,
+    ) {
+        lint_callback!(self, check_struct_def, s);
+        hir_visit::walk_struct_def(self, s);
+        lint_callback!(self, check_struct_def_post, s);
+    }
+
+    fn visit_struct_field(&mut self, s: &'tcx hir::StructField<'tcx>) {
+        self.with_lint_attrs(s.hir_id, &s.attrs, |cx| {
+            lint_callback!(cx, check_struct_field, s);
+            hir_visit::walk_struct_field(cx, s);
+        })
+    }
+
+    fn visit_variant(
+        &mut self,
+        v: &'tcx hir::Variant<'tcx>,
+        g: &'tcx hir::Generics<'tcx>,
+        item_id: hir::HirId,
+    ) {
+        self.with_lint_attrs(v.id, &v.attrs, |cx| {
+            lint_callback!(cx, check_variant, v);
+            hir_visit::walk_variant(cx, v, g, item_id);
+            lint_callback!(cx, check_variant_post, v);
+        })
+    }
+
+    fn visit_ty(&mut self, t: &'tcx hir::Ty<'tcx>) {
+        lint_callback!(self, check_ty, t);
+        hir_visit::walk_ty(self, t);
+    }
+
+    fn visit_name(&mut self, sp: Span, name: Symbol) {
+        lint_callback!(self, check_name, sp, name);
+    }
+
+    fn visit_mod(&mut self, m: &'tcx hir::Mod<'tcx>, s: Span, n: hir::HirId) {
+        if !self.context.only_module {
+            self.process_mod(m, s, n);
+        }
+    }
+
+    fn visit_local(&mut self, l: &'tcx hir::Local<'tcx>) {
+        self.with_lint_attrs(l.hir_id, &l.attrs, |cx| {
+            lint_callback!(cx, check_local, l);
+            hir_visit::walk_local(cx, l);
+        })
+    }
+
+    fn visit_block(&mut self, b: &'tcx hir::Block<'tcx>) {
+        lint_callback!(self, check_block, b);
+        hir_visit::walk_block(self, b);
+        lint_callback!(self, check_block_post, b);
+    }
+
+    fn visit_arm(&mut self, a: &'tcx hir::Arm<'tcx>) {
+        lint_callback!(self, check_arm, a);
+        hir_visit::walk_arm(self, a);
+    }
+
+    fn visit_generic_param(&mut self, p: &'tcx hir::GenericParam<'tcx>) {
+        lint_callback!(self, check_generic_param, p);
+        hir_visit::walk_generic_param(self, p);
+    }
+
+    fn visit_generics(&mut self, g: &'tcx hir::Generics<'tcx>) {
+        lint_callback!(self, check_generics, g);
+        hir_visit::walk_generics(self, g);
+    }
+
+    fn visit_where_predicate(&mut self, p: &'tcx hir::WherePredicate<'tcx>) {
+        lint_callback!(self, check_where_predicate, p);
+        hir_visit::walk_where_predicate(self, p);
+    }
+
+    fn visit_poly_trait_ref(
+        &mut self,
+        t: &'tcx hir::PolyTraitRef<'tcx>,
+        m: hir::TraitBoundModifier,
+    ) {
+        lint_callback!(self, check_poly_trait_ref, t, m);
+        hir_visit::walk_poly_trait_ref(self, t, m);
+    }
+
+    fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
+        let generics = self.context.generics.take();
+        self.context.generics = Some(&trait_item.generics);
+        self.with_lint_attrs(trait_item.hir_id, &trait_item.attrs, |cx| {
+            cx.with_param_env(trait_item.hir_id, |cx| {
+                lint_callback!(cx, check_trait_item, trait_item);
+                hir_visit::walk_trait_item(cx, trait_item);
+                lint_callback!(cx, check_trait_item_post, trait_item);
+            });
+        });
+        self.context.generics = generics;
+    }
+
+    fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
+        let generics = self.context.generics.take();
+        self.context.generics = Some(&impl_item.generics);
+        self.with_lint_attrs(impl_item.hir_id, &impl_item.attrs, |cx| {
+            cx.with_param_env(impl_item.hir_id, |cx| {
+                lint_callback!(cx, check_impl_item, impl_item);
+                hir_visit::walk_impl_item(cx, impl_item);
+                lint_callback!(cx, check_impl_item_post, impl_item);
+            });
+        });
+        self.context.generics = generics;
+    }
+
+    fn visit_lifetime(&mut self, lt: &'tcx hir::Lifetime) {
+        lint_callback!(self, check_lifetime, lt);
+        hir_visit::walk_lifetime(self, lt);
+    }
+
+    fn visit_path(&mut self, p: &'tcx hir::Path<'tcx>, id: hir::HirId) {
+        lint_callback!(self, check_path, p, id);
+        hir_visit::walk_path(self, p);
+    }
+
+    fn visit_attribute(&mut self, attr: &'tcx ast::Attribute) {
+        lint_callback!(self, check_attribute, attr);
+    }
+}
+
+struct LateLintPassObjects<'a> {
+    lints: &'a mut [LateLintPassObject],
+}
+
+#[allow(rustc::lint_pass_impl_without_macro)]
+impl LintPass for LateLintPassObjects<'_> {
+    fn name(&self) -> &'static str {
+        panic!()
+    }
+}
+
+macro_rules! expand_late_lint_pass_impl_methods {
+    ([$hir:tt], [$($(#[$attr:meta])* fn $name:ident($($param:ident: $arg:ty),*);)*]) => (
+        $(fn $name(&mut self, context: &LateContext<$hir>, $($param: $arg),*) {
+            for obj in self.lints.iter_mut() {
+                obj.$name(context, $($param),*);
+            }
+        })*
+    )
+}
+
+macro_rules! late_lint_pass_impl {
+    ([], [$hir:tt], $methods:tt) => {
+        impl<$hir> LateLintPass<$hir> for LateLintPassObjects<'_> {
+            expand_late_lint_pass_impl_methods!([$hir], $methods);
+        }
+    };
+}
+
+crate::late_lint_methods!(late_lint_pass_impl, [], ['tcx]);
+
+fn late_lint_mod_pass<'tcx, T: LateLintPass<'tcx>>(
+    tcx: TyCtxt<'tcx>,
+    module_def_id: LocalDefId,
+    pass: T,
+) {
+    let access_levels = &tcx.privacy_access_levels(LOCAL_CRATE);
+
+    let context = LateContext {
+        tcx,
+        enclosing_body: None,
+        cached_typeck_results: Cell::new(None),
+        param_env: ty::ParamEnv::empty(),
+        access_levels,
+        lint_store: unerased_lint_store(tcx),
+        last_node_with_lint_attrs: tcx.hir().local_def_id_to_hir_id(module_def_id),
+        generics: None,
+        only_module: true,
+    };
+
+    let mut cx = LateContextAndPass { context, pass };
+
+    let (module, span, hir_id) = tcx.hir().get_module(module_def_id);
+    cx.process_mod(module, span, hir_id);
+
+    // Visit the crate attributes
+    if hir_id == hir::CRATE_HIR_ID {
+        walk_list!(cx, visit_attribute, tcx.hir().attrs(hir::CRATE_HIR_ID));
+    }
+}
+
+pub fn late_lint_mod<'tcx, T: LateLintPass<'tcx>>(
+    tcx: TyCtxt<'tcx>,
+    module_def_id: LocalDefId,
+    builtin_lints: T,
+) {
+    if tcx.sess.opts.debugging_opts.no_interleave_lints {
+        // These passes runs in late_lint_crate with -Z no_interleave_lints
+        return;
+    }
+
+    late_lint_mod_pass(tcx, module_def_id, builtin_lints);
+
+    let mut passes: Vec<_> =
+        unerased_lint_store(tcx).late_module_passes.iter().map(|pass| (pass)()).collect();
+
+    if !passes.is_empty() {
+        late_lint_mod_pass(tcx, module_def_id, LateLintPassObjects { lints: &mut passes[..] });
+    }
+}
+
+fn late_lint_pass_crate<'tcx, T: LateLintPass<'tcx>>(tcx: TyCtxt<'tcx>, pass: T) {
+    let access_levels = &tcx.privacy_access_levels(LOCAL_CRATE);
+
+    let krate = tcx.hir().krate();
+
+    let context = LateContext {
+        tcx,
+        enclosing_body: None,
+        cached_typeck_results: Cell::new(None),
+        param_env: ty::ParamEnv::empty(),
+        access_levels,
+        lint_store: unerased_lint_store(tcx),
+        last_node_with_lint_attrs: hir::CRATE_HIR_ID,
+        generics: None,
+        only_module: false,
+    };
+
+    let mut cx = LateContextAndPass { context, pass };
+
+    // Visit the whole crate.
+    cx.with_lint_attrs(hir::CRATE_HIR_ID, &krate.item.attrs, |cx| {
+        // since the root module isn't visited as an item (because it isn't an
+        // item), warn for it here.
+        lint_callback!(cx, check_crate, krate);
+
+        hir_visit::walk_crate(cx, krate);
+
+        lint_callback!(cx, check_crate_post, krate);
+    })
+}
+
+fn late_lint_crate<'tcx, T: LateLintPass<'tcx>>(tcx: TyCtxt<'tcx>, builtin_lints: T) {
+    let mut passes = unerased_lint_store(tcx).late_passes.iter().map(|p| (p)()).collect::<Vec<_>>();
+
+    if !tcx.sess.opts.debugging_opts.no_interleave_lints {
+        if !passes.is_empty() {
+            late_lint_pass_crate(tcx, LateLintPassObjects { lints: &mut passes[..] });
+        }
+
+        late_lint_pass_crate(tcx, builtin_lints);
+    } else {
+        for pass in &mut passes {
+            tcx.sess.prof.extra_verbose_generic_activity("run_late_lint", pass.name()).run(|| {
+                late_lint_pass_crate(tcx, LateLintPassObjects { lints: slice::from_mut(pass) });
+            });
+        }
+
+        let mut passes: Vec<_> =
+            unerased_lint_store(tcx).late_module_passes.iter().map(|pass| (pass)()).collect();
+
+        for pass in &mut passes {
+            tcx.sess.prof.extra_verbose_generic_activity("run_late_module_lint", pass.name()).run(
+                || {
+                    late_lint_pass_crate(tcx, LateLintPassObjects { lints: slice::from_mut(pass) });
+                },
+            );
+        }
+    }
+}
+
+/// Performs lint checking on a crate.
+pub fn check_crate<'tcx, T: LateLintPass<'tcx>>(
+    tcx: TyCtxt<'tcx>,
+    builtin_lints: impl FnOnce() -> T + Send,
+) {
+    join(
+        || {
+            tcx.sess.time("crate_lints", || {
+                // Run whole crate non-incremental lints
+                late_lint_crate(tcx, builtin_lints());
+            });
+        },
+        || {
+            tcx.sess.time("module_lints", || {
+                // Run per-module lints
+                par_iter(&tcx.hir().krate().modules).for_each(|(&module, _)| {
+                    tcx.ensure().lint_mod(tcx.hir().local_def_id(module));
+                });
+            });
+        },
+    );
+}

compiler/rustc_lint/src/levels.rs

@@ -0,0 +1,576 @@
+use crate::context::{CheckLintNameResult, LintStore};
+use crate::late::unerased_lint_store;
+use rustc_ast as ast;
+use rustc_ast::attr;
+use rustc_ast::unwrap_or;
+use rustc_ast_pretty::pprust;
+use rustc_data_structures::fx::FxHashMap;
+use rustc_errors::{struct_span_err, Applicability};
+use rustc_hir as hir;
+use rustc_hir::def_id::{CrateNum, LOCAL_CRATE};
+use rustc_hir::{intravisit, HirId};
+use rustc_middle::hir::map::Map;
+use rustc_middle::lint::LintDiagnosticBuilder;
+use rustc_middle::lint::{struct_lint_level, LintLevelMap, LintLevelSets, LintSet, LintSource};
+use rustc_middle::ty::query::Providers;
+use rustc_middle::ty::TyCtxt;
+use rustc_session::lint::{builtin, Level, Lint, LintId};
+use rustc_session::parse::feature_err;
+use rustc_session::Session;
+use rustc_span::symbol::{sym, Symbol};
+use rustc_span::{source_map::MultiSpan, Span, DUMMY_SP};
+
+use std::cmp;
+
+fn lint_levels(tcx: TyCtxt<'_>, cnum: CrateNum) -> LintLevelMap {
+    assert_eq!(cnum, LOCAL_CRATE);
+    let store = unerased_lint_store(tcx);
+    let levels = LintLevelsBuilder::new(tcx.sess, false, &store);
+    let mut builder = LintLevelMapBuilder { levels, tcx, store };
+    let krate = tcx.hir().krate();
+
+    let push = builder.levels.push(&krate.item.attrs, &store, true);
+    builder.levels.register_id(hir::CRATE_HIR_ID);
+    for macro_def in krate.exported_macros {
+        builder.levels.register_id(macro_def.hir_id);
+    }
+    intravisit::walk_crate(&mut builder, krate);
+    builder.levels.pop(push);
+
+    builder.levels.build_map()
+}
+
+pub struct LintLevelsBuilder<'s> {
+    sess: &'s Session,
+    sets: LintLevelSets,
+    id_to_set: FxHashMap<HirId, u32>,
+    cur: u32,
+    warn_about_weird_lints: bool,
+}
+
+pub struct BuilderPush {
+    prev: u32,
+    pub changed: bool,
+}
+
+impl<'s> LintLevelsBuilder<'s> {
+    pub fn new(sess: &'s Session, warn_about_weird_lints: bool, store: &LintStore) -> Self {
+        let mut builder = LintLevelsBuilder {
+            sess,
+            sets: LintLevelSets::new(),
+            cur: 0,
+            id_to_set: Default::default(),
+            warn_about_weird_lints,
+        };
+        builder.process_command_line(sess, store);
+        assert_eq!(builder.sets.list.len(), 1);
+        builder
+    }
+
+    fn process_command_line(&mut self, sess: &Session, store: &LintStore) {
+        let mut specs = FxHashMap::default();
+        self.sets.lint_cap = sess.opts.lint_cap.unwrap_or(Level::Forbid);
+
+        for &(ref lint_name, level) in &sess.opts.lint_opts {
+            store.check_lint_name_cmdline(sess, &lint_name, level);
+
+            // If the cap is less than this specified level, e.g., if we've got
+            // `--cap-lints allow` but we've also got `-D foo` then we ignore
+            // this specification as the lint cap will set it to allow anyway.
+            let level = cmp::min(level, self.sets.lint_cap);
+
+            let lint_flag_val = Symbol::intern(lint_name);
+
+            let ids = match store.find_lints(&lint_name) {
+                Ok(ids) => ids,
+                Err(_) => continue, // errors handled in check_lint_name_cmdline above
+            };
+            for id in ids {
+                self.check_gated_lint(id, DUMMY_SP);
+                let src = LintSource::CommandLine(lint_flag_val);
+                specs.insert(id, (level, src));
+            }
+        }
+
+        self.sets.list.push(LintSet::CommandLine { specs });
+    }
+
+    /// Pushes a list of AST lint attributes onto this context.
+    ///
+    /// This function will return a `BuilderPush` object which should be passed
+    /// to `pop` when this scope for the attributes provided is exited.
+    ///
+    /// This function will perform a number of tasks:
+    ///
+    /// * It'll validate all lint-related attributes in `attrs`
+    /// * It'll mark all lint-related attributes as used
+    /// * Lint levels will be updated based on the attributes provided
+    /// * Lint attributes are validated, e.g., a `#[forbid]` can't be switched to
+    ///   `#[allow]`
+    ///
+    /// Don't forget to call `pop`!
+    pub fn push(
+        &mut self,
+        attrs: &[ast::Attribute],
+        store: &LintStore,
+        is_crate_node: bool,
+    ) -> BuilderPush {
+        let mut specs = FxHashMap::default();
+        let sess = self.sess;
+        let bad_attr = |span| struct_span_err!(sess, span, E0452, "malformed lint attribute input");
+        for attr in attrs {
+            let level = match Level::from_symbol(attr.name_or_empty()) {
+                None => continue,
+                Some(lvl) => lvl,
+            };
+
+            let meta = unwrap_or!(attr.meta(), continue);
+            self.sess.mark_attr_used(attr);
+
+            let mut metas = unwrap_or!(meta.meta_item_list(), continue);
+
+            if metas.is_empty() {
+                // FIXME (#55112): issue unused-attributes lint for `#[level()]`
+                continue;
+            }
+
+            // Before processing the lint names, look for a reason (RFC 2383)
+            // at the end.
+            let mut reason = None;
+            let tail_li = &metas[metas.len() - 1];
+            if let Some(item) = tail_li.meta_item() {
+                match item.kind {
+                    ast::MetaItemKind::Word => {} // actual lint names handled later
+                    ast::MetaItemKind::NameValue(ref name_value) => {
+                        if item.path == sym::reason {
+                            // found reason, reslice meta list to exclude it
+                            metas = &metas[0..metas.len() - 1];
+                            // FIXME (#55112): issue unused-attributes lint if we thereby
+                            // don't have any lint names (`#[level(reason = "foo")]`)
+                            if let ast::LitKind::Str(rationale, _) = name_value.kind {
+                                if !self.sess.features_untracked().lint_reasons {
+                                    feature_err(
+                                        &self.sess.parse_sess,
+                                        sym::lint_reasons,
+                                        item.span,
+                                        "lint reasons are experimental",
+                                    )
+                                    .emit();
+                                }
+                                reason = Some(rationale);
+                            } else {
+                                bad_attr(name_value.span)
+                                    .span_label(name_value.span, "reason must be a string literal")
+                                    .emit();
+                            }
+                        } else {
+                            bad_attr(item.span)
+                                .span_label(item.span, "bad attribute argument")
+                                .emit();
+                        }
+                    }
+                    ast::MetaItemKind::List(_) => {
+                        bad_attr(item.span).span_label(item.span, "bad attribute argument").emit();
+                    }
+                }
+            }
+
+            for li in metas {
+                let meta_item = match li.meta_item() {
+                    Some(meta_item) if meta_item.is_word() => meta_item,
+                    _ => {
+                        let sp = li.span();
+                        let mut err = bad_attr(sp);
+                        let mut add_label = true;
+                        if let Some(item) = li.meta_item() {
+                            if let ast::MetaItemKind::NameValue(_) = item.kind {
+                                if item.path == sym::reason {
+                                    err.span_label(sp, "reason in lint attribute must come last");
+                                    add_label = false;
+                                }
+                            }
+                        }
+                        if add_label {
+                            err.span_label(sp, "bad attribute argument");
+                        }
+                        err.emit();
+                        continue;
+                    }
+                };
+                let tool_name = if meta_item.path.segments.len() > 1 {
+                    let tool_ident = meta_item.path.segments[0].ident;
+                    if !attr::is_known_lint_tool(tool_ident) {
+                        struct_span_err!(
+                            sess,
+                            tool_ident.span,
+                            E0710,
+                            "an unknown tool name found in scoped lint: `{}`",
+                            pprust::path_to_string(&meta_item.path),
+                        )
+                        .emit();
+                        continue;
+                    }
+
+                    Some(tool_ident.name)
+                } else {
+                    None
+                };
+                let name = meta_item.path.segments.last().expect("empty lint name").ident.name;
+                match store.check_lint_name(&name.as_str(), tool_name) {
+                    CheckLintNameResult::Ok(ids) => {
+                        let src = LintSource::Node(name, li.span(), reason);
+                        for &id in ids {
+                            self.check_gated_lint(id, attr.span);
+                            specs.insert(id, (level, src));
+                        }
+                    }
+
+                    CheckLintNameResult::Tool(result) => {
+                        match result {
+                            Ok(ids) => {
+                                let complete_name = &format!("{}::{}", tool_name.unwrap(), name);
+                                let src = LintSource::Node(
+                                    Symbol::intern(complete_name),
+                                    li.span(),
+                                    reason,
+                                );
+                                for id in ids {
+                                    specs.insert(*id, (level, src));
+                                }
+                            }
+                            Err((Some(ids), new_lint_name)) => {
+                                let lint = builtin::RENAMED_AND_REMOVED_LINTS;
+                                let (lvl, src) =
+                                    self.sets.get_lint_level(lint, self.cur, Some(&specs), &sess);
+                                struct_lint_level(
+                                    self.sess,
+                                    lint,
+                                    lvl,
+                                    src,
+                                    Some(li.span().into()),
+                                    |lint| {
+                                        let msg = format!(
+                                            "lint name `{}` is deprecated \
+                                             and may not have an effect in the future. \
+                                             Also `cfg_attr(cargo-clippy)` won't be necessary anymore",
+                                            name
+                                        );
+                                        lint.build(&msg)
+                                            .span_suggestion(
+                                                li.span(),
+                                                "change it to",
+                                                new_lint_name.to_string(),
+                                                Applicability::MachineApplicable,
+                                            )
+                                            .emit();
+                                    },
+                                );
+
+                                let src = LintSource::Node(
+                                    Symbol::intern(&new_lint_name),
+                                    li.span(),
+                                    reason,
+                                );
+                                for id in ids {
+                                    specs.insert(*id, (level, src));
+                                }
+                            }
+                            Err((None, _)) => {
+                                // If Tool(Err(None, _)) is returned, then either the lint does not
+                                // exist in the tool or the code was not compiled with the tool and
+                                // therefore the lint was never added to the `LintStore`. To detect
+                                // this is the responsibility of the lint tool.
+                            }
+                        }
+                    }
+
+                    _ if !self.warn_about_weird_lints => {}
+
+                    CheckLintNameResult::Warning(msg, renamed) => {
+                        let lint = builtin::RENAMED_AND_REMOVED_LINTS;
+                        let (level, src) =
+                            self.sets.get_lint_level(lint, self.cur, Some(&specs), &sess);
+                        struct_lint_level(
+                            self.sess,
+                            lint,
+                            level,
+                            src,
+                            Some(li.span().into()),
+                            |lint| {
+                                let mut err = lint.build(&msg);
+                                if let Some(new_name) = renamed {
+                                    err.span_suggestion(
+                                        li.span(),
+                                        "use the new name",
+                                        new_name,
+                                        Applicability::MachineApplicable,
+                                    );
+                                }
+                                err.emit();
+                            },
+                        );
+                    }
+                    CheckLintNameResult::NoLint(suggestion) => {
+                        let lint = builtin::UNKNOWN_LINTS;
+                        let (level, src) =
+                            self.sets.get_lint_level(lint, self.cur, Some(&specs), self.sess);
+                        struct_lint_level(
+                            self.sess,
+                            lint,
+                            level,
+                            src,
+                            Some(li.span().into()),
+                            |lint| {
+                                let mut db = lint.build(&format!("unknown lint: `{}`", name));
+                                if let Some(suggestion) = suggestion {
+                                    db.span_suggestion(
+                                        li.span(),
+                                        "did you mean",
+                                        suggestion.to_string(),
+                                        Applicability::MachineApplicable,
+                                    );
+                                }
+                                db.emit();
+                            },
+                        );
+                    }
+                }
+            }
+        }
+
+        if !is_crate_node {
+            for (id, &(level, ref src)) in specs.iter() {
+                if !id.lint.crate_level_only {
+                    continue;
+                }
+
+                let (lint_attr_name, lint_attr_span) = match *src {
+                    LintSource::Node(name, span, _) => (name, span),
+                    _ => continue,
+                };
+
+                let lint = builtin::UNUSED_ATTRIBUTES;
+                let (lint_level, lint_src) =
+                    self.sets.get_lint_level(lint, self.cur, Some(&specs), self.sess);
+                struct_lint_level(
+                    self.sess,
+                    lint,
+                    lint_level,
+                    lint_src,
+                    Some(lint_attr_span.into()),
+                    |lint| {
+                        let mut db = lint.build(&format!(
+                            "{}({}) is ignored unless specified at crate level",
+                            level.as_str(),
+                            lint_attr_name
+                        ));
+                        db.emit();
+                    },
+                );
+                // don't set a separate error for every lint in the group
+                break;
+            }
+        }
+
+        for (id, &(level, ref src)) in specs.iter() {
+            if level == Level::Forbid {
+                continue;
+            }
+            let forbid_src = match self.sets.get_lint_id_level(*id, self.cur, None) {
+                (Some(Level::Forbid), src) => src,
+                _ => continue,
+            };
+            let forbidden_lint_name = match forbid_src {
+                LintSource::Default => id.to_string(),
+                LintSource::Node(name, _, _) => name.to_string(),
+                LintSource::CommandLine(name) => name.to_string(),
+            };
+            let (lint_attr_name, lint_attr_span) = match *src {
+                LintSource::Node(name, span, _) => (name, span),
+                _ => continue,
+            };
+            let mut diag_builder = struct_span_err!(
+                self.sess,
+                lint_attr_span,
+                E0453,
+                "{}({}) overruled by outer forbid({})",
+                level.as_str(),
+                lint_attr_name,
+                forbidden_lint_name
+            );
+            diag_builder.span_label(lint_attr_span, "overruled by previous forbid");
+            match forbid_src {
+                LintSource::Default => {}
+                LintSource::Node(_, forbid_source_span, reason) => {
+                    diag_builder.span_label(forbid_source_span, "`forbid` level set here");
+                    if let Some(rationale) = reason {
+                        diag_builder.note(&rationale.as_str());
+                    }
+                }
+                LintSource::CommandLine(_) => {
+                    diag_builder.note("`forbid` lint level was set on command line");
+                }
+            }
+            diag_builder.emit();
+            // don't set a separate error for every lint in the group
+            break;
+        }
+
+        let prev = self.cur;
+        if !specs.is_empty() {
+            self.cur = self.sets.list.len() as u32;
+            self.sets.list.push(LintSet::Node { specs, parent: prev });
+        }
+
+        BuilderPush { prev, changed: prev != self.cur }
+    }
+
+    /// Checks if the lint is gated on a feature that is not enabled.
+    fn check_gated_lint(&self, lint_id: LintId, span: Span) {
+        if let Some(feature) = lint_id.lint.feature_gate {
+            if !self.sess.features_untracked().enabled(feature) {
+                feature_err(
+                    &self.sess.parse_sess,
+                    feature,
+                    span,
+                    &format!("the `{}` lint is unstable", lint_id.lint.name_lower()),
+                )
+                .emit();
+            }
+        }
+    }
+
+    /// Called after `push` when the scope of a set of attributes are exited.
+    pub fn pop(&mut self, push: BuilderPush) {
+        self.cur = push.prev;
+    }
+
+    /// Find the lint level for a lint.
+    pub fn lint_level(&self, lint: &'static Lint) -> (Level, LintSource) {
+        self.sets.get_lint_level(lint, self.cur, None, self.sess)
+    }
+
+    /// Used to emit a lint-related diagnostic based on the current state of
+    /// this lint context.
+    pub fn struct_lint(
+        &self,
+        lint: &'static Lint,
+        span: Option<MultiSpan>,
+        decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
+    ) {
+        let (level, src) = self.lint_level(lint);
+        struct_lint_level(self.sess, lint, level, src, span, decorate)
+    }
+
+    /// Registers the ID provided with the current set of lints stored in
+    /// this context.
+    pub fn register_id(&mut self, id: HirId) {
+        self.id_to_set.insert(id, self.cur);
+    }
+
+    pub fn build(self) -> LintLevelSets {
+        self.sets
+    }
+
+    pub fn build_map(self) -> LintLevelMap {
+        LintLevelMap { sets: self.sets, id_to_set: self.id_to_set }
+    }
+}
+
+struct LintLevelMapBuilder<'a, 'tcx> {
+    levels: LintLevelsBuilder<'tcx>,
+    tcx: TyCtxt<'tcx>,
+    store: &'a LintStore,
+}
+
+impl LintLevelMapBuilder<'_, '_> {
+    fn with_lint_attrs<F>(&mut self, id: hir::HirId, attrs: &[ast::Attribute], f: F)
+    where
+        F: FnOnce(&mut Self),
+    {
+        let is_crate_hir = id == hir::CRATE_HIR_ID;
+        let push = self.levels.push(attrs, self.store, is_crate_hir);
+        if push.changed {
+            self.levels.register_id(id);
+        }
+        f(self);
+        self.levels.pop(push);
+    }
+}
+
+impl<'tcx> intravisit::Visitor<'tcx> for LintLevelMapBuilder<'_, 'tcx> {
+    type Map = Map<'tcx>;
+
+    fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
+        intravisit::NestedVisitorMap::All(self.tcx.hir())
+    }
+
+    fn visit_param(&mut self, param: &'tcx hir::Param<'tcx>) {
+        self.with_lint_attrs(param.hir_id, &param.attrs, |builder| {
+            intravisit::walk_param(builder, param);
+        });
+    }
+
+    fn visit_item(&mut self, it: &'tcx hir::Item<'tcx>) {
+        self.with_lint_attrs(it.hir_id, &it.attrs, |builder| {
+            intravisit::walk_item(builder, it);
+        });
+    }
+
+    fn visit_foreign_item(&mut self, it: &'tcx hir::ForeignItem<'tcx>) {
+        self.with_lint_attrs(it.hir_id, &it.attrs, |builder| {
+            intravisit::walk_foreign_item(builder, it);
+        })
+    }
+
+    fn visit_expr(&mut self, e: &'tcx hir::Expr<'tcx>) {
+        self.with_lint_attrs(e.hir_id, &e.attrs, |builder| {
+            intravisit::walk_expr(builder, e);
+        })
+    }
+
+    fn visit_struct_field(&mut self, s: &'tcx hir::StructField<'tcx>) {
+        self.with_lint_attrs(s.hir_id, &s.attrs, |builder| {
+            intravisit::walk_struct_field(builder, s);
+        })
+    }
+
+    fn visit_variant(
+        &mut self,
+        v: &'tcx hir::Variant<'tcx>,
+        g: &'tcx hir::Generics<'tcx>,
+        item_id: hir::HirId,
+    ) {
+        self.with_lint_attrs(v.id, &v.attrs, |builder| {
+            intravisit::walk_variant(builder, v, g, item_id);
+        })
+    }
+
+    fn visit_local(&mut self, l: &'tcx hir::Local<'tcx>) {
+        self.with_lint_attrs(l.hir_id, &l.attrs, |builder| {
+            intravisit::walk_local(builder, l);
+        })
+    }
+
+    fn visit_arm(&mut self, a: &'tcx hir::Arm<'tcx>) {
+        self.with_lint_attrs(a.hir_id, &a.attrs, |builder| {
+            intravisit::walk_arm(builder, a);
+        })
+    }
+
+    fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
+        self.with_lint_attrs(trait_item.hir_id, &trait_item.attrs, |builder| {
+            intravisit::walk_trait_item(builder, trait_item);
+        });
+    }
+
+    fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
+        self.with_lint_attrs(impl_item.hir_id, &impl_item.attrs, |builder| {
+            intravisit::walk_impl_item(builder, impl_item);
+        });
+    }
+}
+
+pub fn provide(providers: &mut Providers) {
+    providers.lint_levels = lint_levels;
+}

compiler/rustc_lint/src/lib.rs

@@ -0,0 +1,464 @@
+//! Lints, aka compiler warnings.
+//!
+//! A 'lint' check is a kind of miscellaneous constraint that a user _might_
+//! want to enforce, but might reasonably want to permit as well, on a
+//! module-by-module basis. They contrast with static constraints enforced by
+//! other phases of the compiler, which are generally required to hold in order
+//! to compile the program at all.
+//!
+//! Most lints can be written as [LintPass] instances. These run after
+//! all other analyses. The `LintPass`es built into rustc are defined
+//! within [rustc_session::lint::builtin],
+//! which has further comments on how to add such a lint.
+//! rustc can also load user-defined lint plugins via the plugin mechanism.
+//!
+//! Some of rustc's lints are defined elsewhere in the compiler and work by
+//! calling `add_lint()` on the overall `Session` object. This works when
+//! it happens before the main lint pass, which emits the lints stored by
+//! `add_lint()`. To emit lints after the main lint pass (from codegen, for
+//! example) requires more effort. See `emit_lint` and `GatherNodeLevels`
+//! in `context.rs`.
+//!
+//! Some code also exists in [rustc_session::lint], [rustc_middle::lint].
+//!
+//! ## Note
+//!
+//! This API is completely unstable and subject to change.
+
+#![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
+#![cfg_attr(test, feature(test))]
+#![feature(bool_to_option)]
+#![feature(box_syntax)]
+#![feature(crate_visibility_modifier)]
+#![feature(iter_order_by)]
+#![feature(never_type)]
+#![feature(nll)]
+#![feature(or_patterns)]
+#![recursion_limit = "256"]
+
+#[macro_use]
+extern crate rustc_middle;
+#[macro_use]
+extern crate rustc_session;
+
+mod array_into_iter;
+pub mod builtin;
+mod context;
+mod early;
+mod internal;
+mod late;
+mod levels;
+mod non_ascii_idents;
+mod nonstandard_style;
+mod passes;
+mod redundant_semicolon;
+mod types;
+mod unused;
+
+use rustc_ast as ast;
+use rustc_hir as hir;
+use rustc_hir::def_id::LocalDefId;
+use rustc_middle::ty::query::Providers;
+use rustc_middle::ty::TyCtxt;
+use rustc_session::lint::builtin::{
+    BARE_TRAIT_OBJECTS, BROKEN_INTRA_DOC_LINKS, ELIDED_LIFETIMES_IN_PATHS,
+    EXPLICIT_OUTLIVES_REQUIREMENTS, INVALID_CODEBLOCK_ATTRIBUTES, MISSING_DOC_CODE_EXAMPLES,
+    PRIVATE_DOC_TESTS,
+};
+use rustc_span::symbol::{Ident, Symbol};
+use rustc_span::Span;
+
+use array_into_iter::ArrayIntoIter;
+use builtin::*;
+use internal::*;
+use non_ascii_idents::*;
+use nonstandard_style::*;
+use redundant_semicolon::*;
+use types::*;
+use unused::*;
+
+/// Useful for other parts of the compiler / Clippy.
+pub use builtin::SoftLints;
+pub use context::{CheckLintNameResult, EarlyContext, LateContext, LintContext, LintStore};
+pub use early::check_ast_crate;
+pub use late::check_crate;
+pub use passes::{EarlyLintPass, LateLintPass};
+pub use rustc_session::lint::Level::{self, *};
+pub use rustc_session::lint::{BufferedEarlyLint, FutureIncompatibleInfo, Lint, LintId};
+pub use rustc_session::lint::{LintArray, LintPass};
+
+pub fn provide(providers: &mut Providers) {
+    levels::provide(providers);
+    *providers = Providers { lint_mod, ..*providers };
+}
+
+fn lint_mod(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
+    late::late_lint_mod(tcx, module_def_id, BuiltinCombinedModuleLateLintPass::new());
+}
+
+macro_rules! pre_expansion_lint_passes {
+    ($macro:path, $args:tt) => {
+        $macro!($args, [KeywordIdents: KeywordIdents,]);
+    };
+}
+
+macro_rules! early_lint_passes {
+    ($macro:path, $args:tt) => {
+        $macro!(
+            $args,
+            [
+                UnusedParens: UnusedParens,
+                UnusedBraces: UnusedBraces,
+                UnusedImportBraces: UnusedImportBraces,
+                UnsafeCode: UnsafeCode,
+                AnonymousParameters: AnonymousParameters,
+                EllipsisInclusiveRangePatterns: EllipsisInclusiveRangePatterns::default(),
+                NonCamelCaseTypes: NonCamelCaseTypes,
+                DeprecatedAttr: DeprecatedAttr::new(),
+                WhileTrue: WhileTrue,
+                NonAsciiIdents: NonAsciiIdents,
+                IncompleteFeatures: IncompleteFeatures,
+                RedundantSemicolons: RedundantSemicolons,
+                UnusedDocComment: UnusedDocComment,
+            ]
+        );
+    };
+}
+
+macro_rules! declare_combined_early_pass {
+    ([$name:ident], $passes:tt) => (
+        early_lint_methods!(declare_combined_early_lint_pass, [pub $name, $passes]);
+    )
+}
+
+pre_expansion_lint_passes!(declare_combined_early_pass, [BuiltinCombinedPreExpansionLintPass]);
+early_lint_passes!(declare_combined_early_pass, [BuiltinCombinedEarlyLintPass]);
+
+macro_rules! late_lint_passes {
+    ($macro:path, $args:tt) => {
+        $macro!(
+            $args,
+            [
+                // FIXME: Look into regression when this is used as a module lint
+                // May Depend on constants elsewhere
+                UnusedBrokenConst: UnusedBrokenConst,
+                // Uses attr::is_used which is untracked, can't be an incremental module pass.
+                UnusedAttributes: UnusedAttributes::new(),
+                // Needs to run after UnusedAttributes as it marks all `feature` attributes as used.
+                UnstableFeatures: UnstableFeatures,
+                // Tracks state across modules
+                UnnameableTestItems: UnnameableTestItems::new(),
+                // Tracks attributes of parents
+                MissingDoc: MissingDoc::new(),
+                // Depends on access levels
+                // FIXME: Turn the computation of types which implement Debug into a query
+                // and change this to a module lint pass
+                MissingDebugImplementations: MissingDebugImplementations::default(),
+                ArrayIntoIter: ArrayIntoIter,
+                ClashingExternDeclarations: ClashingExternDeclarations::new(),
+            ]
+        );
+    };
+}
+
+macro_rules! late_lint_mod_passes {
+    ($macro:path, $args:tt) => {
+        $macro!(
+            $args,
+            [
+                HardwiredLints: HardwiredLints,
+                ImproperCTypesDeclarations: ImproperCTypesDeclarations,
+                ImproperCTypesDefinitions: ImproperCTypesDefinitions,
+                VariantSizeDifferences: VariantSizeDifferences,
+                BoxPointers: BoxPointers,
+                PathStatements: PathStatements,
+                // Depends on referenced function signatures in expressions
+                UnusedResults: UnusedResults,
+                NonUpperCaseGlobals: NonUpperCaseGlobals,
+                NonShorthandFieldPatterns: NonShorthandFieldPatterns,
+                UnusedAllocation: UnusedAllocation,
+                // Depends on types used in type definitions
+                MissingCopyImplementations: MissingCopyImplementations,
+                // Depends on referenced function signatures in expressions
+                MutableTransmutes: MutableTransmutes,
+                TypeAliasBounds: TypeAliasBounds,
+                TrivialConstraints: TrivialConstraints,
+                TypeLimits: TypeLimits::new(),
+                NonSnakeCase: NonSnakeCase,
+                InvalidNoMangleItems: InvalidNoMangleItems,
+                // Depends on access levels
+                UnreachablePub: UnreachablePub,
+                ExplicitOutlivesRequirements: ExplicitOutlivesRequirements,
+                InvalidValue: InvalidValue,
+            ]
+        );
+    };
+}
+
+macro_rules! declare_combined_late_pass {
+    ([$v:vis $name:ident], $passes:tt) => (
+        late_lint_methods!(declare_combined_late_lint_pass, [$v $name, $passes], ['tcx]);
+    )
+}
+
+// FIXME: Make a separate lint type which do not require typeck tables
+late_lint_passes!(declare_combined_late_pass, [pub BuiltinCombinedLateLintPass]);
+
+late_lint_mod_passes!(declare_combined_late_pass, [BuiltinCombinedModuleLateLintPass]);
+
+pub fn new_lint_store(no_interleave_lints: bool, internal_lints: bool) -> LintStore {
+    let mut lint_store = LintStore::new();
+
+    register_builtins(&mut lint_store, no_interleave_lints);
+    if internal_lints {
+        register_internals(&mut lint_store);
+    }
+
+    lint_store
+}
+
+/// Tell the `LintStore` about all the built-in lints (the ones
+/// defined in this crate and the ones defined in
+/// `rustc_session::lint::builtin`).
+fn register_builtins(store: &mut LintStore, no_interleave_lints: bool) {
+    macro_rules! add_lint_group {
+        ($name:expr, $($lint:ident),*) => (
+            store.register_group(false, $name, None, vec![$(LintId::of($lint)),*]);
+        )
+    }
+
+    macro_rules! register_pass {
+        ($method:ident, $ty:ident, $constructor:expr) => {
+            store.register_lints(&$ty::get_lints());
+            store.$method(|| box $constructor);
+        };
+    }
+
+    macro_rules! register_passes {
+        ($method:ident, [$($passes:ident: $constructor:expr,)*]) => (
+            $(
+                register_pass!($method, $passes, $constructor);
+            )*
+        )
+    }
+
+    if no_interleave_lints {
+        pre_expansion_lint_passes!(register_passes, register_pre_expansion_pass);
+        early_lint_passes!(register_passes, register_early_pass);
+        late_lint_passes!(register_passes, register_late_pass);
+        late_lint_mod_passes!(register_passes, register_late_mod_pass);
+    } else {
+        store.register_lints(&BuiltinCombinedPreExpansionLintPass::get_lints());
+        store.register_lints(&BuiltinCombinedEarlyLintPass::get_lints());
+        store.register_lints(&BuiltinCombinedModuleLateLintPass::get_lints());
+        store.register_lints(&BuiltinCombinedLateLintPass::get_lints());
+    }
+
+    add_lint_group!(
+        "nonstandard_style",
+        NON_CAMEL_CASE_TYPES,
+        NON_SNAKE_CASE,
+        NON_UPPER_CASE_GLOBALS
+    );
+
+    add_lint_group!(
+        "unused",
+        UNUSED_IMPORTS,
+        UNUSED_VARIABLES,
+        UNUSED_ASSIGNMENTS,
+        DEAD_CODE,
+        UNUSED_MUT,
+        UNREACHABLE_CODE,
+        UNREACHABLE_PATTERNS,
+        OVERLAPPING_PATTERNS,
+        UNUSED_MUST_USE,
+        UNUSED_UNSAFE,
+        PATH_STATEMENTS,
+        UNUSED_ATTRIBUTES,
+        UNUSED_MACROS,
+        UNUSED_ALLOCATION,
+        UNUSED_DOC_COMMENTS,
+        UNUSED_EXTERN_CRATES,
+        UNUSED_FEATURES,
+        UNUSED_LABELS,
+        UNUSED_PARENS,
+        UNUSED_BRACES,
+        REDUNDANT_SEMICOLONS
+    );
+
+    add_lint_group!(
+        "rust_2018_idioms",
+        BARE_TRAIT_OBJECTS,
+        UNUSED_EXTERN_CRATES,
+        ELLIPSIS_INCLUSIVE_RANGE_PATTERNS,
+        ELIDED_LIFETIMES_IN_PATHS,
+        EXPLICIT_OUTLIVES_REQUIREMENTS // FIXME(#52665, #47816) not always applicable and not all
+                                       // macros are ready for this yet.
+                                       // UNREACHABLE_PUB,
+
+                                       // FIXME macro crates are not up for this yet, too much
+                                       // breakage is seen if we try to encourage this lint.
+                                       // MACRO_USE_EXTERN_CRATE
+    );
+
+    add_lint_group!(
+        "rustdoc",
+        BROKEN_INTRA_DOC_LINKS,
+        INVALID_CODEBLOCK_ATTRIBUTES,
+        MISSING_DOC_CODE_EXAMPLES,
+        PRIVATE_DOC_TESTS
+    );
+
+    // Register renamed and removed lints.
+    store.register_renamed("single_use_lifetime", "single_use_lifetimes");
+    store.register_renamed("elided_lifetime_in_path", "elided_lifetimes_in_paths");
+    store.register_renamed("bare_trait_object", "bare_trait_objects");
+    store.register_renamed("unstable_name_collision", "unstable_name_collisions");
+    store.register_renamed("unused_doc_comment", "unused_doc_comments");
+    store.register_renamed("async_idents", "keyword_idents");
+    store.register_renamed("exceeding_bitshifts", "arithmetic_overflow");
+    store.register_renamed("redundant_semicolon", "redundant_semicolons");
+    store.register_renamed("intra_doc_link_resolution_failure", "broken_intra_doc_links");
+    store.register_removed("unknown_features", "replaced by an error");
+    store.register_removed("unsigned_negation", "replaced by negate_unsigned feature gate");
+    store.register_removed("negate_unsigned", "cast a signed value instead");
+    store.register_removed("raw_pointer_derive", "using derive with raw pointers is ok");
+    // Register lint group aliases.
+    store.register_group_alias("nonstandard_style", "bad_style");
+    // This was renamed to `raw_pointer_derive`, which was then removed,
+    // so it is also considered removed.
+    store.register_removed("raw_pointer_deriving", "using derive with raw pointers is ok");
+    store.register_removed("drop_with_repr_extern", "drop flags have been removed");
+    store.register_removed("fat_ptr_transmutes", "was accidentally removed back in 2014");
+    store.register_removed("deprecated_attr", "use `deprecated` instead");
+    store.register_removed(
+        "transmute_from_fn_item_types",
+        "always cast functions before transmuting them",
+    );
+    store.register_removed(
+        "hr_lifetime_in_assoc_type",
+        "converted into hard error, see issue #33685 \
+         <https://github.com/rust-lang/rust/issues/33685> for more information",
+    );
+    store.register_removed(
+        "inaccessible_extern_crate",
+        "converted into hard error, see issue #36886 \
+         <https://github.com/rust-lang/rust/issues/36886> for more information",
+    );
+    store.register_removed(
+        "super_or_self_in_global_path",
+        "converted into hard error, see issue #36888 \
+         <https://github.com/rust-lang/rust/issues/36888> for more information",
+    );
+    store.register_removed(
+        "overlapping_inherent_impls",
+        "converted into hard error, see issue #36889 \
+         <https://github.com/rust-lang/rust/issues/36889> for more information",
+    );
+    store.register_removed(
+        "illegal_floating_point_constant_pattern",
+        "converted into hard error, see issue #36890 \
+         <https://github.com/rust-lang/rust/issues/36890> for more information",
+    );
+    store.register_removed(
+        "illegal_struct_or_enum_constant_pattern",
+        "converted into hard error, see issue #36891 \
+         <https://github.com/rust-lang/rust/issues/36891> for more information",
+    );
+    store.register_removed(
+        "lifetime_underscore",
+        "converted into hard error, see issue #36892 \
+         <https://github.com/rust-lang/rust/issues/36892> for more information",
+    );
+    store.register_removed(
+        "extra_requirement_in_impl",
+        "converted into hard error, see issue #37166 \
+         <https://github.com/rust-lang/rust/issues/37166> for more information",
+    );
+    store.register_removed(
+        "legacy_imports",
+        "converted into hard error, see issue #38260 \
+         <https://github.com/rust-lang/rust/issues/38260> for more information",
+    );
+    store.register_removed(
+        "coerce_never",
+        "converted into hard error, see issue #48950 \
+         <https://github.com/rust-lang/rust/issues/48950> for more information",
+    );
+    store.register_removed(
+        "resolve_trait_on_defaulted_unit",
+        "converted into hard error, see issue #48950 \
+         <https://github.com/rust-lang/rust/issues/48950> for more information",
+    );
+    store.register_removed(
+        "private_no_mangle_fns",
+        "no longer a warning, `#[no_mangle]` functions always exported",
+    );
+    store.register_removed(
+        "private_no_mangle_statics",
+        "no longer a warning, `#[no_mangle]` statics always exported",
+    );
+    store.register_removed("bad_repr", "replaced with a generic attribute input check");
+    store.register_removed(
+        "duplicate_matcher_binding_name",
+        "converted into hard error, see issue #57742 \
+         <https://github.com/rust-lang/rust/issues/57742> for more information",
+    );
+    store.register_removed(
+        "incoherent_fundamental_impls",
+        "converted into hard error, see issue #46205 \
+         <https://github.com/rust-lang/rust/issues/46205> for more information",
+    );
+    store.register_removed(
+        "legacy_constructor_visibility",
+        "converted into hard error, see issue #39207 \
+         <https://github.com/rust-lang/rust/issues/39207> for more information",
+    );
+    store.register_removed(
+        "legacy_directory_ownership",
+        "converted into hard error, see issue #37872 \
+         <https://github.com/rust-lang/rust/issues/37872> for more information",
+    );
+    store.register_removed(
+        "safe_extern_statics",
+        "converted into hard error, see issue #36247 \
+         <https://github.com/rust-lang/rust/issues/36247> for more information",
+    );
+    store.register_removed(
+        "parenthesized_params_in_types_and_modules",
+        "converted into hard error, see issue #42238 \
+         <https://github.com/rust-lang/rust/issues/42238> for more information",
+    );
+    store.register_removed(
+        "duplicate_macro_exports",
+        "converted into hard error, see issue #35896 \
+         <https://github.com/rust-lang/rust/issues/35896> for more information",
+    );
+    store.register_removed(
+        "nested_impl_trait",
+        "converted into hard error, see issue #59014 \
+         <https://github.com/rust-lang/rust/issues/59014> for more information",
+    );
+    store.register_removed("plugin_as_library", "plugins have been deprecated and retired");
+}
+
+fn register_internals(store: &mut LintStore) {
+    store.register_lints(&DefaultHashTypes::get_lints());
+    store.register_early_pass(|| box DefaultHashTypes::new());
+    store.register_lints(&LintPassImpl::get_lints());
+    store.register_early_pass(|| box LintPassImpl);
+    store.register_lints(&TyTyKind::get_lints());
+    store.register_late_pass(|| box TyTyKind);
+    store.register_group(
+        false,
+        "rustc::internal",
+        None,
+        vec![
+            LintId::of(DEFAULT_HASH_TYPES),
+            LintId::of(USAGE_OF_TY_TYKIND),
+            LintId::of(LINT_PASS_IMPL_WITHOUT_MACRO),
+            LintId::of(TY_PASS_BY_REFERENCE),
+            LintId::of(USAGE_OF_QUALIFIED_TY),
+        ],
+    );
+}

compiler/rustc_lint/src/non_ascii_idents.rs

@@ -0,0 +1,240 @@
+use crate::{EarlyContext, EarlyLintPass, LintContext};
+use rustc_ast as ast;
+use rustc_data_structures::fx::FxHashMap;
+use rustc_span::symbol::Symbol;
+
+declare_lint! {
+    pub NON_ASCII_IDENTS,
+    Allow,
+    "detects non-ASCII identifiers",
+    crate_level_only
+}
+
+declare_lint! {
+    pub UNCOMMON_CODEPOINTS,
+    Warn,
+    "detects uncommon Unicode codepoints in identifiers",
+    crate_level_only
+}
+
+declare_lint! {
+    pub CONFUSABLE_IDENTS,
+    Warn,
+    "detects visually confusable pairs between identifiers",
+    crate_level_only
+}
+
+declare_lint! {
+    pub MIXED_SCRIPT_CONFUSABLES,
+    Warn,
+    "detects Unicode scripts whose mixed script confusables codepoints are solely used",
+    crate_level_only
+}
+
+declare_lint_pass!(NonAsciiIdents => [NON_ASCII_IDENTS, UNCOMMON_CODEPOINTS, CONFUSABLE_IDENTS, MIXED_SCRIPT_CONFUSABLES]);
+
+impl EarlyLintPass for NonAsciiIdents {
+    fn check_crate(&mut self, cx: &EarlyContext<'_>, _: &ast::Crate) {
+        use rustc_session::lint::Level;
+        use rustc_span::Span;
+        use std::collections::BTreeMap;
+        use unicode_security::GeneralSecurityProfile;
+
+        let check_non_ascii_idents = cx.builder.lint_level(NON_ASCII_IDENTS).0 != Level::Allow;
+        let check_uncommon_codepoints =
+            cx.builder.lint_level(UNCOMMON_CODEPOINTS).0 != Level::Allow;
+        let check_confusable_idents = cx.builder.lint_level(CONFUSABLE_IDENTS).0 != Level::Allow;
+        let check_mixed_script_confusables =
+            cx.builder.lint_level(MIXED_SCRIPT_CONFUSABLES).0 != Level::Allow;
+
+        if !check_non_ascii_idents
+            && !check_uncommon_codepoints
+            && !check_confusable_idents
+            && !check_mixed_script_confusables
+        {
+            return;
+        }
+
+        let mut has_non_ascii_idents = false;
+        let symbols = cx.sess.parse_sess.symbol_gallery.symbols.lock();
+
+        // Sort by `Span` so that error messages make sense with respect to the
+        // order of identifier locations in the code.
+        let mut symbols: Vec<_> = symbols.iter().collect();
+        symbols.sort_by_key(|k| k.1);
+
+        for (symbol, &sp) in symbols.iter() {
+            let symbol_str = symbol.as_str();
+            if symbol_str.is_ascii() {
+                continue;
+            }
+            has_non_ascii_idents = true;
+            cx.struct_span_lint(NON_ASCII_IDENTS, sp, |lint| {
+                lint.build("identifier contains non-ASCII characters").emit()
+            });
+            if check_uncommon_codepoints
+                && !symbol_str.chars().all(GeneralSecurityProfile::identifier_allowed)
+            {
+                cx.struct_span_lint(UNCOMMON_CODEPOINTS, sp, |lint| {
+                    lint.build("identifier contains uncommon Unicode codepoints").emit()
+                })
+            }
+        }
+
+        if has_non_ascii_idents && check_confusable_idents {
+            let mut skeleton_map: FxHashMap<Symbol, (Symbol, Span, bool)> =
+                FxHashMap::with_capacity_and_hasher(symbols.len(), Default::default());
+            let mut skeleton_buf = String::new();
+
+            for (&symbol, &sp) in symbols.iter() {
+                use unicode_security::confusable_detection::skeleton;
+
+                let symbol_str = symbol.as_str();
+                let is_ascii = symbol_str.is_ascii();
+
+                // Get the skeleton as a `Symbol`.
+                skeleton_buf.clear();
+                skeleton_buf.extend(skeleton(&symbol_str));
+                let skeleton_sym = if *symbol_str == *skeleton_buf {
+                    symbol
+                } else {
+                    Symbol::intern(&skeleton_buf)
+                };
+
+                skeleton_map
+                    .entry(skeleton_sym)
+                    .and_modify(|(existing_symbol, existing_span, existing_is_ascii)| {
+                        if !*existing_is_ascii || !is_ascii {
+                            cx.struct_span_lint(CONFUSABLE_IDENTS, sp, |lint| {
+                                lint.build(&format!(
+                                    "identifier pair considered confusable between `{}` and `{}`",
+                                    existing_symbol.as_str(),
+                                    symbol.as_str()
+                                ))
+                                .span_label(
+                                    *existing_span,
+                                    "this is where the previous identifier occurred",
+                                )
+                                .emit();
+                            });
+                        }
+                        if *existing_is_ascii && !is_ascii {
+                            *existing_symbol = symbol;
+                            *existing_span = sp;
+                            *existing_is_ascii = is_ascii;
+                        }
+                    })
+                    .or_insert((symbol, sp, is_ascii));
+            }
+        }
+
+        if has_non_ascii_idents && check_mixed_script_confusables {
+            use unicode_security::is_potential_mixed_script_confusable_char;
+            use unicode_security::mixed_script::AugmentedScriptSet;
+
+            #[derive(Clone)]
+            enum ScriptSetUsage {
+                Suspicious(Vec<char>, Span),
+                Verified,
+            }
+
+            let mut script_states: FxHashMap<AugmentedScriptSet, ScriptSetUsage> =
+                FxHashMap::default();
+            let latin_augmented_script_set = AugmentedScriptSet::for_char('A');
+            script_states.insert(latin_augmented_script_set, ScriptSetUsage::Verified);
+
+            let mut has_suspicous = false;
+            for (symbol, &sp) in symbols.iter() {
+                let symbol_str = symbol.as_str();
+                for ch in symbol_str.chars() {
+                    if ch.is_ascii() {
+                        // all ascii characters are covered by exception.
+                        continue;
+                    }
+                    if !GeneralSecurityProfile::identifier_allowed(ch) {
+                        // this character is covered by `uncommon_codepoints` lint.
+                        continue;
+                    }
+                    let augmented_script_set = AugmentedScriptSet::for_char(ch);
+                    script_states
+                        .entry(augmented_script_set)
+                        .and_modify(|existing_state| {
+                            if let ScriptSetUsage::Suspicious(ch_list, _) = existing_state {
+                                if is_potential_mixed_script_confusable_char(ch) {
+                                    ch_list.push(ch);
+                                } else {
+                                    *existing_state = ScriptSetUsage::Verified;
+                                }
+                            }
+                        })
+                        .or_insert_with(|| {
+                            if !is_potential_mixed_script_confusable_char(ch) {
+                                ScriptSetUsage::Verified
+                            } else {
+                                has_suspicous = true;
+                                ScriptSetUsage::Suspicious(vec![ch], sp)
+                            }
+                        });
+                }
+            }
+
+            if has_suspicous {
+                let verified_augmented_script_sets = script_states
+                    .iter()
+                    .flat_map(|(k, v)| match v {
+                        ScriptSetUsage::Verified => Some(*k),
+                        _ => None,
+                    })
+                    .collect::<Vec<_>>();
+
+                // we're sorting the output here.
+                let mut lint_reports: BTreeMap<(Span, Vec<char>), AugmentedScriptSet> =
+                    BTreeMap::new();
+
+                'outerloop: for (augment_script_set, usage) in script_states {
+                    let (mut ch_list, sp) = match usage {
+                        ScriptSetUsage::Verified => continue,
+                        ScriptSetUsage::Suspicious(ch_list, sp) => (ch_list, sp),
+                    };
+
+                    if augment_script_set.is_all() {
+                        continue;
+                    }
+
+                    for existing in verified_augmented_script_sets.iter() {
+                        if existing.is_all() {
+                            continue;
+                        }
+                        let mut intersect = *existing;
+                        intersect.intersect_with(augment_script_set);
+                        if !intersect.is_empty() && !intersect.is_all() {
+                            continue 'outerloop;
+                        }
+                    }
+
+                    ch_list.sort();
+                    ch_list.dedup();
+                    lint_reports.insert((sp, ch_list), augment_script_set);
+                }
+
+                for ((sp, ch_list), script_set) in lint_reports {
+                    cx.struct_span_lint(MIXED_SCRIPT_CONFUSABLES, sp, |lint| {
+                        let message = format!(
+                            "The usage of Script Group `{}` in this crate consists solely of mixed script confusables",
+                            script_set);
+                        let mut note = "The usage includes ".to_string();
+                        for (idx, ch) in ch_list.into_iter().enumerate() {
+                            if idx != 0 {
+                                note += ", ";
+                            }
+                            let char_info = format!("'{}' (U+{:04X})", ch, ch as u32);
+                            note += &char_info;
+                        }
+                        note += ".";
+                        lint.build(&message).note(&note).note("Please recheck to make sure their usages are indeed what you want.").emit()
+                    });
+                }
+            }
+        }
+    }
+}

compiler/rustc_lint/src/nonstandard_style.rs

@@ -0,0 +1,456 @@
+use crate::{EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext};
+use rustc_ast as ast;
+use rustc_attr as attr;
+use rustc_errors::Applicability;
+use rustc_hir as hir;
+use rustc_hir::def::{DefKind, Res};
+use rustc_hir::intravisit::FnKind;
+use rustc_hir::{GenericParamKind, PatKind};
+use rustc_middle::ty;
+use rustc_span::symbol::sym;
+use rustc_span::{symbol::Ident, BytePos, Span};
+use rustc_target::spec::abi::Abi;
+
+#[derive(PartialEq)]
+pub enum MethodLateContext {
+    TraitAutoImpl,
+    TraitImpl,
+    PlainImpl,
+}
+
+pub fn method_context(cx: &LateContext<'_>, id: hir::HirId) -> MethodLateContext {
+    let def_id = cx.tcx.hir().local_def_id(id);
+    let item = cx.tcx.associated_item(def_id);
+    match item.container {
+        ty::TraitContainer(..) => MethodLateContext::TraitAutoImpl,
+        ty::ImplContainer(cid) => match cx.tcx.impl_trait_ref(cid) {
+            Some(_) => MethodLateContext::TraitImpl,
+            None => MethodLateContext::PlainImpl,
+        },
+    }
+}
+
+declare_lint! {
+    pub NON_CAMEL_CASE_TYPES,
+    Warn,
+    "types, variants, traits and type parameters should have camel case names"
+}
+
+declare_lint_pass!(NonCamelCaseTypes => [NON_CAMEL_CASE_TYPES]);
+
+fn char_has_case(c: char) -> bool {
+    c.is_lowercase() || c.is_uppercase()
+}
+
+fn is_camel_case(name: &str) -> bool {
+    let name = name.trim_matches('_');
+    if name.is_empty() {
+        return true;
+    }
+
+    // start with a non-lowercase letter rather than non-uppercase
+    // ones (some scripts don't have a concept of upper/lowercase)
+    !name.chars().next().unwrap().is_lowercase()
+        && !name.contains("__")
+        && !name.chars().collect::<Vec<_>>().windows(2).any(|pair| {
+            // contains a capitalisable character followed by, or preceded by, an underscore
+            char_has_case(pair[0]) && pair[1] == '_' || char_has_case(pair[1]) && pair[0] == '_'
+        })
+}
+
+fn to_camel_case(s: &str) -> String {
+    s.trim_matches('_')
+        .split('_')
+        .filter(|component| !component.is_empty())
+        .map(|component| {
+            let mut camel_cased_component = String::new();
+
+            let mut new_word = true;
+            let mut prev_is_lower_case = true;
+
+            for c in component.chars() {
+                // Preserve the case if an uppercase letter follows a lowercase letter, so that
+                // `camelCase` is converted to `CamelCase`.
+                if prev_is_lower_case && c.is_uppercase() {
+                    new_word = true;
+                }
+
+                if new_word {
+                    camel_cased_component.push_str(&c.to_uppercase().to_string());
+                } else {
+                    camel_cased_component.push_str(&c.to_lowercase().to_string());
+                }
+
+                prev_is_lower_case = c.is_lowercase();
+                new_word = false;
+            }
+
+            camel_cased_component
+        })
+        .fold((String::new(), None), |(acc, prev): (String, Option<String>), next| {
+            // separate two components with an underscore if their boundary cannot
+            // be distinguished using a uppercase/lowercase case distinction
+            let join = if let Some(prev) = prev {
+                let l = prev.chars().last().unwrap();
+                let f = next.chars().next().unwrap();
+                !char_has_case(l) && !char_has_case(f)
+            } else {
+                false
+            };
+            (acc + if join { "_" } else { "" } + &next, Some(next))
+        })
+        .0
+}
+
+impl NonCamelCaseTypes {
+    fn check_case(&self, cx: &EarlyContext<'_>, sort: &str, ident: &Ident) {
+        let name = &ident.name.as_str();
+
+        if !is_camel_case(name) {
+            cx.struct_span_lint(NON_CAMEL_CASE_TYPES, ident.span, |lint| {
+                let msg = format!("{} `{}` should have an upper camel case name", sort, name);
+                lint.build(&msg)
+                    .span_suggestion(
+                        ident.span,
+                        "convert the identifier to upper camel case",
+                        to_camel_case(name),
+                        Applicability::MaybeIncorrect,
+                    )
+                    .emit()
+            })
+        }
+    }
+}
+
+impl EarlyLintPass for NonCamelCaseTypes {
+    fn check_item(&mut self, cx: &EarlyContext<'_>, it: &ast::Item) {
+        let has_repr_c = it
+            .attrs
+            .iter()
+            .any(|attr| attr::find_repr_attrs(&cx.sess, attr).contains(&attr::ReprC));
+
+        if has_repr_c {
+            return;
+        }
+
+        match it.kind {
+            ast::ItemKind::TyAlias(..)
+            | ast::ItemKind::Enum(..)
+            | ast::ItemKind::Struct(..)
+            | ast::ItemKind::Union(..) => self.check_case(cx, "type", &it.ident),
+            ast::ItemKind::Trait(..) => self.check_case(cx, "trait", &it.ident),
+            _ => (),
+        }
+    }
+
+    fn check_trait_item(&mut self, cx: &EarlyContext<'_>, it: &ast::AssocItem) {
+        if let ast::AssocItemKind::TyAlias(..) = it.kind {
+            self.check_case(cx, "associated type", &it.ident);
+        }
+    }
+
+    fn check_variant(&mut self, cx: &EarlyContext<'_>, v: &ast::Variant) {
+        self.check_case(cx, "variant", &v.ident);
+    }
+
+    fn check_generic_param(&mut self, cx: &EarlyContext<'_>, param: &ast::GenericParam) {
+        if let ast::GenericParamKind::Type { .. } = param.kind {
+            self.check_case(cx, "type parameter", &param.ident);
+        }
+    }
+}
+
+declare_lint! {
+    pub NON_SNAKE_CASE,
+    Warn,
+    "variables, methods, functions, lifetime parameters and modules should have snake case names"
+}
+
+declare_lint_pass!(NonSnakeCase => [NON_SNAKE_CASE]);
+
+impl NonSnakeCase {
+    fn to_snake_case(mut str: &str) -> String {
+        let mut words = vec![];
+        // Preserve leading underscores
+        str = str.trim_start_matches(|c: char| {
+            if c == '_' {
+                words.push(String::new());
+                true
+            } else {
+                false
+            }
+        });
+        for s in str.split('_') {
+            let mut last_upper = false;
+            let mut buf = String::new();
+            if s.is_empty() {
+                continue;
+            }
+            for ch in s.chars() {
+                if !buf.is_empty() && buf != "'" && ch.is_uppercase() && !last_upper {
+                    words.push(buf);
+                    buf = String::new();
+                }
+                last_upper = ch.is_uppercase();
+                buf.extend(ch.to_lowercase());
+            }
+            words.push(buf);
+        }
+        words.join("_")
+    }
+
+    /// Checks if a given identifier is snake case, and reports a diagnostic if not.
+    fn check_snake_case(&self, cx: &LateContext<'_>, sort: &str, ident: &Ident) {
+        fn is_snake_case(ident: &str) -> bool {
+            if ident.is_empty() {
+                return true;
+            }
+            let ident = ident.trim_start_matches('\'');
+            let ident = ident.trim_matches('_');
+
+            let mut allow_underscore = true;
+            ident.chars().all(|c| {
+                allow_underscore = match c {
+                    '_' if !allow_underscore => return false,
+                    '_' => false,
+                    // It would be more obvious to use `c.is_lowercase()`,
+                    // but some characters do not have a lowercase form
+                    c if !c.is_uppercase() => true,
+                    _ => return false,
+                };
+                true
+            })
+        }
+
+        let name = &ident.name.as_str();
+
+        if !is_snake_case(name) {
+            cx.struct_span_lint(NON_SNAKE_CASE, ident.span, |lint| {
+                let sc = NonSnakeCase::to_snake_case(name);
+                let msg = format!("{} `{}` should have a snake case name", sort, name);
+                let mut err = lint.build(&msg);
+                // We have a valid span in almost all cases, but we don't have one when linting a crate
+                // name provided via the command line.
+                if !ident.span.is_dummy() {
+                    err.span_suggestion(
+                        ident.span,
+                        "convert the identifier to snake case",
+                        sc,
+                        Applicability::MaybeIncorrect,
+                    );
+                } else {
+                    err.help(&format!("convert the identifier to snake case: `{}`", sc));
+                }
+
+                err.emit();
+            });
+        }
+    }
+}
+
+impl<'tcx> LateLintPass<'tcx> for NonSnakeCase {
+    fn check_mod(
+        &mut self,
+        cx: &LateContext<'_>,
+        _: &'tcx hir::Mod<'tcx>,
+        _: Span,
+        id: hir::HirId,
+    ) {
+        if id != hir::CRATE_HIR_ID {
+            return;
+        }
+
+        let crate_ident = if let Some(name) = &cx.tcx.sess.opts.crate_name {
+            Some(Ident::from_str(name))
+        } else {
+            cx.sess()
+                .find_by_name(&cx.tcx.hir().attrs(hir::CRATE_HIR_ID), sym::crate_name)
+                .and_then(|attr| attr.meta())
+                .and_then(|meta| {
+                    meta.name_value_literal().and_then(|lit| {
+                        if let ast::LitKind::Str(name, ..) = lit.kind {
+                            // Discard the double quotes surrounding the literal.
+                            let sp = cx
+                                .sess()
+                                .source_map()
+                                .span_to_snippet(lit.span)
+                                .ok()
+                                .and_then(|snippet| {
+                                    let left = snippet.find('"')?;
+                                    let right =
+                                        snippet.rfind('"').map(|pos| snippet.len() - pos)?;
+
+                                    Some(
+                                        lit.span
+                                            .with_lo(lit.span.lo() + BytePos(left as u32 + 1))
+                                            .with_hi(lit.span.hi() - BytePos(right as u32)),
+                                    )
+                                })
+                                .unwrap_or_else(|| lit.span);
+
+                            Some(Ident::new(name, sp))
+                        } else {
+                            None
+                        }
+                    })
+                })
+        };
+
+        if let Some(ident) = &crate_ident {
+            self.check_snake_case(cx, "crate", ident);
+        }
+    }
+
+    fn check_generic_param(&mut self, cx: &LateContext<'_>, param: &hir::GenericParam<'_>) {
+        if let GenericParamKind::Lifetime { .. } = param.kind {
+            self.check_snake_case(cx, "lifetime", &param.name.ident());
+        }
+    }
+
+    fn check_fn(
+        &mut self,
+        cx: &LateContext<'_>,
+        fk: FnKind<'_>,
+        _: &hir::FnDecl<'_>,
+        _: &hir::Body<'_>,
+        _: Span,
+        id: hir::HirId,
+    ) {
+        match &fk {
+            FnKind::Method(ident, ..) => match method_context(cx, id) {
+                MethodLateContext::PlainImpl => {
+                    self.check_snake_case(cx, "method", ident);
+                }
+                MethodLateContext::TraitAutoImpl => {
+                    self.check_snake_case(cx, "trait method", ident);
+                }
+                _ => (),
+            },
+            FnKind::ItemFn(ident, _, header, _, attrs) => {
+                // Skip foreign-ABI #[no_mangle] functions (Issue #31924)
+                if header.abi != Abi::Rust && cx.sess().contains_name(attrs, sym::no_mangle) {
+                    return;
+                }
+                self.check_snake_case(cx, "function", ident);
+            }
+            FnKind::Closure(_) => (),
+        }
+    }
+
+    fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
+        if let hir::ItemKind::Mod(_) = it.kind {
+            self.check_snake_case(cx, "module", &it.ident);
+        }
+    }
+
+    fn check_trait_item(&mut self, cx: &LateContext<'_>, item: &hir::TraitItem<'_>) {
+        if let hir::TraitItemKind::Fn(_, hir::TraitFn::Required(pnames)) = item.kind {
+            self.check_snake_case(cx, "trait method", &item.ident);
+            for param_name in pnames {
+                self.check_snake_case(cx, "variable", param_name);
+            }
+        }
+    }
+
+    fn check_pat(&mut self, cx: &LateContext<'_>, p: &hir::Pat<'_>) {
+        if let &PatKind::Binding(_, hid, ident, _) = &p.kind {
+            if let hir::Node::Pat(parent_pat) = cx.tcx.hir().get(cx.tcx.hir().get_parent_node(hid))
+            {
+                if let PatKind::Struct(_, field_pats, _) = &parent_pat.kind {
+                    for field in field_pats.iter() {
+                        if field.ident != ident {
+                            // Only check if a new name has been introduced, to avoid warning
+                            // on both the struct definition and this pattern.
+                            self.check_snake_case(cx, "variable", &ident);
+                        }
+                    }
+                    return;
+                }
+            }
+            self.check_snake_case(cx, "variable", &ident);
+        }
+    }
+
+    fn check_struct_def(&mut self, cx: &LateContext<'_>, s: &hir::VariantData<'_>) {
+        for sf in s.fields() {
+            self.check_snake_case(cx, "structure field", &sf.ident);
+        }
+    }
+}
+
+declare_lint! {
+    pub NON_UPPER_CASE_GLOBALS,
+    Warn,
+    "static constants should have uppercase identifiers"
+}
+
+declare_lint_pass!(NonUpperCaseGlobals => [NON_UPPER_CASE_GLOBALS]);
+
+impl NonUpperCaseGlobals {
+    fn check_upper_case(cx: &LateContext<'_>, sort: &str, ident: &Ident) {
+        let name = &ident.name.as_str();
+        if name.chars().any(|c| c.is_lowercase()) {
+            cx.struct_span_lint(NON_UPPER_CASE_GLOBALS, ident.span, |lint| {
+                let uc = NonSnakeCase::to_snake_case(&name).to_uppercase();
+                lint.build(&format!("{} `{}` should have an upper case name", sort, name))
+                    .span_suggestion(
+                        ident.span,
+                        "convert the identifier to upper case",
+                        uc,
+                        Applicability::MaybeIncorrect,
+                    )
+                    .emit();
+            })
+        }
+    }
+}
+
+impl<'tcx> LateLintPass<'tcx> for NonUpperCaseGlobals {
+    fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
+        match it.kind {
+            hir::ItemKind::Static(..) if !cx.sess().contains_name(&it.attrs, sym::no_mangle) => {
+                NonUpperCaseGlobals::check_upper_case(cx, "static variable", &it.ident);
+            }
+            hir::ItemKind::Const(..) => {
+                NonUpperCaseGlobals::check_upper_case(cx, "constant", &it.ident);
+            }
+            _ => {}
+        }
+    }
+
+    fn check_trait_item(&mut self, cx: &LateContext<'_>, ti: &hir::TraitItem<'_>) {
+        if let hir::TraitItemKind::Const(..) = ti.kind {
+            NonUpperCaseGlobals::check_upper_case(cx, "associated constant", &ti.ident);
+        }
+    }
+
+    fn check_impl_item(&mut self, cx: &LateContext<'_>, ii: &hir::ImplItem<'_>) {
+        if let hir::ImplItemKind::Const(..) = ii.kind {
+            NonUpperCaseGlobals::check_upper_case(cx, "associated constant", &ii.ident);
+        }
+    }
+
+    fn check_pat(&mut self, cx: &LateContext<'_>, p: &hir::Pat<'_>) {
+        // Lint for constants that look like binding identifiers (#7526)
+        if let PatKind::Path(hir::QPath::Resolved(None, ref path)) = p.kind {
+            if let Res::Def(DefKind::Const, _) = path.res {
+                if path.segments.len() == 1 {
+                    NonUpperCaseGlobals::check_upper_case(
+                        cx,
+                        "constant in pattern",
+                        &path.segments[0].ident,
+                    );
+                }
+            }
+        }
+    }
+
+    fn check_generic_param(&mut self, cx: &LateContext<'_>, param: &hir::GenericParam<'_>) {
+        if let GenericParamKind::Const { .. } = param.kind {
+            NonUpperCaseGlobals::check_upper_case(cx, "const parameter", &param.name.ident());
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests;

compiler/rustc_lint/src/nonstandard_style/tests.rs

@@ -0,0 +1,21 @@
+use super::{is_camel_case, to_camel_case};
+
+#[test]
+fn camel_case() {
+    assert!(!is_camel_case("userData"));
+    assert_eq!(to_camel_case("userData"), "UserData");
+
+    assert!(is_camel_case("X86_64"));
+
+    assert!(!is_camel_case("X86__64"));
+    assert_eq!(to_camel_case("X86__64"), "X86_64");
+
+    assert!(!is_camel_case("Abc_123"));
+    assert_eq!(to_camel_case("Abc_123"), "Abc123");
+
+    assert!(!is_camel_case("A1_b2_c3"));
+    assert_eq!(to_camel_case("A1_b2_c3"), "A1B2C3");
+
+    assert!(!is_camel_case("ONE_TWO_THREE"));
+    assert_eq!(to_camel_case("ONE_TWO_THREE"), "OneTwoThree");
+}

compiler/rustc_lint/src/passes.rs

@@ -0,0 +1,285 @@
+use crate::context::{EarlyContext, LateContext};
+
+use rustc_ast as ast;
+use rustc_data_structures::sync;
+use rustc_hir as hir;
+use rustc_session::lint::builtin::HardwiredLints;
+use rustc_session::lint::LintPass;
+use rustc_span::symbol::{Ident, Symbol};
+use rustc_span::Span;
+
+#[macro_export]
+macro_rules! late_lint_methods {
+    ($macro:path, $args:tt, [$hir:tt]) => (
+        $macro!($args, [$hir], [
+            fn check_param(a: &$hir hir::Param<$hir>);
+            fn check_body(a: &$hir hir::Body<$hir>);
+            fn check_body_post(a: &$hir hir::Body<$hir>);
+            fn check_name(a: Span, b: Symbol);
+            fn check_crate(a: &$hir hir::Crate<$hir>);
+            fn check_crate_post(a: &$hir hir::Crate<$hir>);
+            fn check_mod(a: &$hir hir::Mod<$hir>, b: Span, c: hir::HirId);
+            fn check_mod_post(a: &$hir hir::Mod<$hir>, b: Span, c: hir::HirId);
+            fn check_foreign_item(a: &$hir hir::ForeignItem<$hir>);
+            fn check_foreign_item_post(a: &$hir hir::ForeignItem<$hir>);
+            fn check_item(a: &$hir hir::Item<$hir>);
+            fn check_item_post(a: &$hir hir::Item<$hir>);
+            fn check_local(a: &$hir hir::Local<$hir>);
+            fn check_block(a: &$hir hir::Block<$hir>);
+            fn check_block_post(a: &$hir hir::Block<$hir>);
+            fn check_stmt(a: &$hir hir::Stmt<$hir>);
+            fn check_arm(a: &$hir hir::Arm<$hir>);
+            fn check_pat(a: &$hir hir::Pat<$hir>);
+            fn check_expr(a: &$hir hir::Expr<$hir>);
+            fn check_expr_post(a: &$hir hir::Expr<$hir>);
+            fn check_ty(a: &$hir hir::Ty<$hir>);
+            fn check_generic_param(a: &$hir hir::GenericParam<$hir>);
+            fn check_generics(a: &$hir hir::Generics<$hir>);
+            fn check_where_predicate(a: &$hir hir::WherePredicate<$hir>);
+            fn check_poly_trait_ref(a: &$hir hir::PolyTraitRef<$hir>, b: hir::TraitBoundModifier);
+            fn check_fn(
+                a: rustc_hir::intravisit::FnKind<$hir>,
+                b: &$hir hir::FnDecl<$hir>,
+                c: &$hir hir::Body<$hir>,
+                d: Span,
+                e: hir::HirId);
+            fn check_fn_post(
+                a: rustc_hir::intravisit::FnKind<$hir>,
+                b: &$hir hir::FnDecl<$hir>,
+                c: &$hir hir::Body<$hir>,
+                d: Span,
+                e: hir::HirId
+            );
+            fn check_trait_item(a: &$hir hir::TraitItem<$hir>);
+            fn check_trait_item_post(a: &$hir hir::TraitItem<$hir>);
+            fn check_impl_item(a: &$hir hir::ImplItem<$hir>);
+            fn check_impl_item_post(a: &$hir hir::ImplItem<$hir>);
+            fn check_struct_def(a: &$hir hir::VariantData<$hir>);
+            fn check_struct_def_post(a: &$hir hir::VariantData<$hir>);
+            fn check_struct_field(a: &$hir hir::StructField<$hir>);
+            fn check_variant(a: &$hir hir::Variant<$hir>);
+            fn check_variant_post(a: &$hir hir::Variant<$hir>);
+            fn check_lifetime(a: &$hir hir::Lifetime);
+            fn check_path(a: &$hir hir::Path<$hir>, b: hir::HirId);
+            fn check_attribute(a: &$hir ast::Attribute);
+
+            /// Called when entering a syntax node that can have lint attributes such
+            /// as `#[allow(...)]`. Called with *all* the attributes of that node.
+            fn enter_lint_attrs(a: &$hir [ast::Attribute]);
+
+            /// Counterpart to `enter_lint_attrs`.
+            fn exit_lint_attrs(a: &$hir [ast::Attribute]);
+        ]);
+    )
+}
+
+/// Trait for types providing lint checks.
+///
+/// Each `check` method checks a single syntax node, and should not
+/// invoke methods recursively (unlike `Visitor`). By default they
+/// do nothing.
+//
+// FIXME: eliminate the duplication with `Visitor`. But this also
+// contains a few lint-specific methods with no equivalent in `Visitor`.
+
+macro_rules! expand_lint_pass_methods {
+    ($context:ty, [$($(#[$attr:meta])* fn $name:ident($($param:ident: $arg:ty),*);)*]) => (
+        $(#[inline(always)] fn $name(&mut self, _: $context, $(_: $arg),*) {})*
+    )
+}
+
+macro_rules! declare_late_lint_pass {
+    ([], [$hir:tt], [$($methods:tt)*]) => (
+        pub trait LateLintPass<$hir>: LintPass {
+            expand_lint_pass_methods!(&LateContext<$hir>, [$($methods)*]);
+        }
+    )
+}
+
+late_lint_methods!(declare_late_lint_pass, [], ['tcx]);
+
+impl LateLintPass<'_> for HardwiredLints {}
+
+#[macro_export]
+macro_rules! expand_combined_late_lint_pass_method {
+    ([$($passes:ident),*], $self: ident, $name: ident, $params:tt) => ({
+        $($self.$passes.$name $params;)*
+    })
+}
+
+#[macro_export]
+macro_rules! expand_combined_late_lint_pass_methods {
+    ($passes:tt, [$($(#[$attr:meta])* fn $name:ident($($param:ident: $arg:ty),*);)*]) => (
+        $(fn $name(&mut self, context: &LateContext<'tcx>, $($param: $arg),*) {
+            expand_combined_late_lint_pass_method!($passes, self, $name, (context, $($param),*));
+        })*
+    )
+}
+
+#[macro_export]
+macro_rules! declare_combined_late_lint_pass {
+    ([$v:vis $name:ident, [$($passes:ident: $constructor:expr,)*]], [$hir:tt], $methods:tt) => (
+        #[allow(non_snake_case)]
+        $v struct $name {
+            $($passes: $passes,)*
+        }
+
+        impl $name {
+            $v fn new() -> Self {
+                Self {
+                    $($passes: $constructor,)*
+                }
+            }
+
+            $v fn get_lints() -> LintArray {
+                let mut lints = Vec::new();
+                $(lints.extend_from_slice(&$passes::get_lints());)*
+                lints
+            }
+        }
+
+        impl<'tcx> LateLintPass<'tcx> for $name {
+            expand_combined_late_lint_pass_methods!([$($passes),*], $methods);
+        }
+
+        #[allow(rustc::lint_pass_impl_without_macro)]
+        impl LintPass for $name {
+            fn name(&self) -> &'static str {
+                panic!()
+            }
+        }
+    )
+}
+
+#[macro_export]
+macro_rules! early_lint_methods {
+    ($macro:path, $args:tt) => (
+        $macro!($args, [
+            fn check_param(a: &ast::Param);
+            fn check_ident(a: Ident);
+            fn check_crate(a: &ast::Crate);
+            fn check_crate_post(a: &ast::Crate);
+            fn check_mod(a: &ast::Mod, b: Span, c: ast::NodeId);
+            fn check_mod_post(a: &ast::Mod, b: Span, c: ast::NodeId);
+            fn check_foreign_item(a: &ast::ForeignItem);
+            fn check_foreign_item_post(a: &ast::ForeignItem);
+            fn check_item(a: &ast::Item);
+            fn check_item_post(a: &ast::Item);
+            fn check_local(a: &ast::Local);
+            fn check_block(a: &ast::Block);
+            fn check_block_post(a: &ast::Block);
+            fn check_stmt(a: &ast::Stmt);
+            fn check_arm(a: &ast::Arm);
+            fn check_pat(a: &ast::Pat);
+            fn check_anon_const(a: &ast::AnonConst);
+            fn check_pat_post(a: &ast::Pat);
+            fn check_expr(a: &ast::Expr);
+            fn check_expr_post(a: &ast::Expr);
+            fn check_ty(a: &ast::Ty);
+            fn check_generic_param(a: &ast::GenericParam);
+            fn check_generics(a: &ast::Generics);
+            fn check_where_predicate(a: &ast::WherePredicate);
+            fn check_poly_trait_ref(a: &ast::PolyTraitRef,
+                                    b: &ast::TraitBoundModifier);
+            fn check_fn(a: rustc_ast::visit::FnKind<'_>, c: Span, d_: ast::NodeId);
+            fn check_fn_post(
+                a: rustc_ast::visit::FnKind<'_>,
+                c: Span,
+                d: ast::NodeId
+            );
+            fn check_trait_item(a: &ast::AssocItem);
+            fn check_trait_item_post(a: &ast::AssocItem);
+            fn check_impl_item(a: &ast::AssocItem);
+            fn check_impl_item_post(a: &ast::AssocItem);
+            fn check_struct_def(a: &ast::VariantData);
+            fn check_struct_def_post(a: &ast::VariantData);
+            fn check_struct_field(a: &ast::StructField);
+            fn check_variant(a: &ast::Variant);
+            fn check_variant_post(a: &ast::Variant);
+            fn check_lifetime(a: &ast::Lifetime);
+            fn check_path(a: &ast::Path, b: ast::NodeId);
+            fn check_attribute(a: &ast::Attribute);
+            fn check_mac_def(a: &ast::MacroDef, b: ast::NodeId);
+            fn check_mac(a: &ast::MacCall);
+
+            /// Called when entering a syntax node that can have lint attributes such
+            /// as `#[allow(...)]`. Called with *all* the attributes of that node.
+            fn enter_lint_attrs(a: &[ast::Attribute]);
+
+            /// Counterpart to `enter_lint_attrs`.
+            fn exit_lint_attrs(a: &[ast::Attribute]);
+        ]);
+    )
+}
+
+macro_rules! expand_early_lint_pass_methods {
+    ($context:ty, [$($(#[$attr:meta])* fn $name:ident($($param:ident: $arg:ty),*);)*]) => (
+        $(#[inline(always)] fn $name(&mut self, _: $context, $(_: $arg),*) {})*
+    )
+}
+
+macro_rules! declare_early_lint_pass {
+    ([], [$($methods:tt)*]) => (
+        pub trait EarlyLintPass: LintPass {
+            expand_early_lint_pass_methods!(&EarlyContext<'_>, [$($methods)*]);
+        }
+    )
+}
+
+early_lint_methods!(declare_early_lint_pass, []);
+
+#[macro_export]
+macro_rules! expand_combined_early_lint_pass_method {
+    ([$($passes:ident),*], $self: ident, $name: ident, $params:tt) => ({
+        $($self.$passes.$name $params;)*
+    })
+}
+
+#[macro_export]
+macro_rules! expand_combined_early_lint_pass_methods {
+    ($passes:tt, [$($(#[$attr:meta])* fn $name:ident($($param:ident: $arg:ty),*);)*]) => (
+        $(fn $name(&mut self, context: &EarlyContext<'_>, $($param: $arg),*) {
+            expand_combined_early_lint_pass_method!($passes, self, $name, (context, $($param),*));
+        })*
+    )
+}
+
+#[macro_export]
+macro_rules! declare_combined_early_lint_pass {
+    ([$v:vis $name:ident, [$($passes:ident: $constructor:expr,)*]], $methods:tt) => (
+        #[allow(non_snake_case)]
+        $v struct $name {
+            $($passes: $passes,)*
+        }
+
+        impl $name {
+            $v fn new() -> Self {
+                Self {
+                    $($passes: $constructor,)*
+                }
+            }
+
+            $v fn get_lints() -> LintArray {
+                let mut lints = Vec::new();
+                $(lints.extend_from_slice(&$passes::get_lints());)*
+                lints
+            }
+        }
+
+        impl EarlyLintPass for $name {
+            expand_combined_early_lint_pass_methods!([$($passes),*], $methods);
+        }
+
+        #[allow(rustc::lint_pass_impl_without_macro)]
+        impl LintPass for $name {
+            fn name(&self) -> &'static str {
+                panic!()
+            }
+        }
+    )
+}
+
+/// A lint pass boxed up as a trait object.
+pub type EarlyLintPassObject = Box<dyn EarlyLintPass + sync::Send + sync::Sync + 'static>;
+pub type LateLintPassObject =
+    Box<dyn for<'tcx> LateLintPass<'tcx> + sync::Send + sync::Sync + 'static>;

compiler/rustc_lint/src/redundant_semicolon.rs

@@ -0,0 +1,41 @@
+use crate::{EarlyContext, EarlyLintPass, LintContext};
+use rustc_ast::{Block, StmtKind};
+use rustc_errors::Applicability;
+use rustc_span::Span;
+
+declare_lint! {
+    pub REDUNDANT_SEMICOLONS,
+    Warn,
+    "detects unnecessary trailing semicolons"
+}
+
+declare_lint_pass!(RedundantSemicolons => [REDUNDANT_SEMICOLONS]);
+
+impl EarlyLintPass for RedundantSemicolons {
+    fn check_block(&mut self, cx: &EarlyContext<'_>, block: &Block) {
+        let mut seq = None;
+        for stmt in block.stmts.iter() {
+            match (&stmt.kind, &mut seq) {
+                (StmtKind::Empty, None) => seq = Some((stmt.span, false)),
+                (StmtKind::Empty, Some(seq)) => *seq = (seq.0.to(stmt.span), true),
+                (_, seq) => maybe_lint_redundant_semis(cx, seq),
+            }
+        }
+        maybe_lint_redundant_semis(cx, &mut seq);
+    }
+}
+
+fn maybe_lint_redundant_semis(cx: &EarlyContext<'_>, seq: &mut Option<(Span, bool)>) {
+    if let Some((span, multiple)) = seq.take() {
+        cx.struct_span_lint(REDUNDANT_SEMICOLONS, span, |lint| {
+            let (msg, rem) = if multiple {
+                ("unnecessary trailing semicolons", "remove these semicolons")
+            } else {
+                ("unnecessary trailing semicolon", "remove this semicolon")
+            };
+            lint.build(msg)
+                .span_suggestion(span, rem, String::new(), Applicability::MaybeIncorrect)
+                .emit();
+        });
+    }
+}