rustc_typeck to rustc_hir_analysis

compiler/rustc_hir_analysis/src/check_unused.rs

@@ -0,0 +1,187 @@
+use crate::errors::{ExternCrateNotIdiomatic, UnusedExternCrate};
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_hir as hir;
+use rustc_hir::def::DefKind;
+use rustc_hir::def_id::{DefId, LocalDefId};
+use rustc_middle::ty::TyCtxt;
+use rustc_session::lint;
+use rustc_span::{Span, Symbol};
+
+pub fn check_crate(tcx: TyCtxt<'_>) {
+    let mut used_trait_imports: FxHashSet<LocalDefId> = FxHashSet::default();
+
+    for item_def_id in tcx.hir().body_owners() {
+        let imports = tcx.used_trait_imports(item_def_id);
+        debug!("GatherVisitor: item_def_id={:?} with imports {:#?}", item_def_id, imports);
+        used_trait_imports.extend(imports.iter());
+    }
+
+    for &id in tcx.maybe_unused_trait_imports(()) {
+        debug_assert_eq!(tcx.def_kind(id), DefKind::Use);
+        if tcx.visibility(id).is_public() {
+            continue;
+        }
+        if used_trait_imports.contains(&id) {
+            continue;
+        }
+        let item = tcx.hir().expect_item(id);
+        if item.span.is_dummy() {
+            continue;
+        }
+        let hir::ItemKind::Use(path, _) = item.kind else { unreachable!() };
+        tcx.struct_span_lint_hir(lint::builtin::UNUSED_IMPORTS, item.hir_id(), path.span, |lint| {
+            let msg = if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(path.span) {
+                format!("unused import: `{}`", snippet)
+            } else {
+                "unused import".to_owned()
+            };
+            lint.build(&msg).emit();
+        });
+    }
+
+    unused_crates_lint(tcx);
+}
+
+fn unused_crates_lint(tcx: TyCtxt<'_>) {
+    let lint = lint::builtin::UNUSED_EXTERN_CRATES;
+
+    // Collect first the crates that are completely unused.  These we
+    // can always suggest removing (no matter which edition we are
+    // in).
+    let unused_extern_crates: FxHashMap<LocalDefId, Span> = tcx
+        .maybe_unused_extern_crates(())
+        .iter()
+        .filter(|&&(def_id, _)| {
+            // The `def_id` here actually was calculated during resolution (at least
+            // at the time of this writing) and is being shipped to us via a side
+            // channel of the tcx. There may have been extra expansion phases,
+            // however, which ended up removing the `def_id` *after* expansion.
+            //
+            // As a result we need to verify that `def_id` is indeed still valid for
+            // our AST and actually present in the HIR map. If it's not there then
+            // there's safely nothing to warn about, and otherwise we carry on with
+            // our execution.
+            //
+            // Note that if we carry through to the `extern_mod_stmt_cnum` query
+            // below it'll cause a panic because `def_id` is actually bogus at this
+            // point in time otherwise.
+            if tcx.hir().find(tcx.hir().local_def_id_to_hir_id(def_id)).is_none() {
+                return false;
+            }
+            true
+        })
+        .filter(|&&(def_id, _)| {
+            tcx.extern_mod_stmt_cnum(def_id).map_or(true, |cnum| {
+                !tcx.is_compiler_builtins(cnum)
+                    && !tcx.is_panic_runtime(cnum)
+                    && !tcx.has_global_allocator(cnum)
+                    && !tcx.has_panic_handler(cnum)
+            })
+        })
+        .cloned()
+        .collect();
+
+    // Collect all the extern crates (in a reliable order).
+    let mut crates_to_lint = vec![];
+
+    for id in tcx.hir().items() {
+        if matches!(tcx.def_kind(id.def_id), DefKind::ExternCrate) {
+            let item = tcx.hir().item(id);
+            if let hir::ItemKind::ExternCrate(orig_name) = item.kind {
+                crates_to_lint.push(ExternCrateToLint {
+                    def_id: item.def_id.to_def_id(),
+                    span: item.span,
+                    orig_name,
+                    warn_if_unused: !item.ident.as_str().starts_with('_'),
+                });
+            }
+        }
+    }
+
+    let extern_prelude = &tcx.resolutions(()).extern_prelude;
+
+    for extern_crate in &crates_to_lint {
+        let def_id = extern_crate.def_id.expect_local();
+        let item = tcx.hir().expect_item(def_id);
+
+        // If the crate is fully unused, we suggest removing it altogether.
+        // We do this in any edition.
+        if extern_crate.warn_if_unused {
+            if let Some(&span) = unused_extern_crates.get(&def_id) {
+                // Removal suggestion span needs to include attributes (Issue #54400)
+                let id = tcx.hir().local_def_id_to_hir_id(def_id);
+                let span_with_attrs = tcx
+                    .hir()
+                    .attrs(id)
+                    .iter()
+                    .map(|attr| attr.span)
+                    .fold(span, |acc, attr_span| acc.to(attr_span));
+
+                tcx.emit_spanned_lint(lint, id, span, UnusedExternCrate { span: span_with_attrs });
+                continue;
+            }
+        }
+
+        // If we are not in Rust 2018 edition, then we don't make any further
+        // suggestions.
+        if !tcx.sess.rust_2018() {
+            continue;
+        }
+
+        // If the extern crate isn't in the extern prelude,
+        // there is no way it can be written as a `use`.
+        let orig_name = extern_crate.orig_name.unwrap_or(item.ident.name);
+        if !extern_prelude.get(&orig_name).map_or(false, |from_item| !from_item) {
+            continue;
+        }
+
+        // If the extern crate is renamed, then we cannot suggest replacing it with a use as this
+        // would not insert the new name into the prelude, where other imports in the crate may be
+        // expecting it.
+        if extern_crate.orig_name.is_some() {
+            continue;
+        }
+
+        let id = tcx.hir().local_def_id_to_hir_id(def_id);
+        // If the extern crate has any attributes, they may have funky
+        // semantics we can't faithfully represent using `use` (most
+        // notably `#[macro_use]`). Ignore it.
+        if !tcx.hir().attrs(id).is_empty() {
+            continue;
+        }
+
+        let base_replacement = match extern_crate.orig_name {
+            Some(orig_name) => format!("use {} as {};", orig_name, item.ident.name),
+            None => format!("use {};", item.ident.name),
+        };
+        let vis = tcx.sess.source_map().span_to_snippet(item.vis_span).unwrap_or_default();
+        let add_vis = |to| if vis.is_empty() { to } else { format!("{} {}", vis, to) };
+        tcx.emit_spanned_lint(
+            lint,
+            id,
+            extern_crate.span,
+            ExternCrateNotIdiomatic {
+                span: extern_crate.span,
+                msg_code: add_vis("use".to_string()),
+                suggestion_code: add_vis(base_replacement),
+            },
+        );
+    }
+}
+
+struct ExternCrateToLint {
+    /// `DefId` of the extern crate
+    def_id: DefId,
+
+    /// span from the item
+    span: Span,
+
+    /// if `Some`, then this is renamed (`extern crate orig_name as
+    /// crate_name`), and -- perhaps surprisingly -- this stores the
+    /// *original* name (`item.name` will contain the new name)
+    orig_name: Option<Symbol>,
+
+    /// if `false`, the original name started with `_`, so we shouldn't lint
+    /// about it going unused (but we should still emit idiom lints).
+    warn_if_unused: bool,
+}