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Auto merge of #107251 - dingxiangfei2009:let-chain-rescope, r=jieyouxu

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Rescope temp lifetime in if-let into IfElse with migration lint

Tracking issue #124085

This PR shortens the temporary lifetime to cover only the pattern matching and consequent branch of a `if let`.

At the expression location, means that the lifetime is shortened from previously the deepest enclosing block or statement in Edition 2021. This warrants an Edition change.

Coming with the Edition change, this patch also implements an edition lint to warn about the change and a safe rewrite suggestion to preserve the 2021 semantics in most cases.

Related to #103108.
Related crater runs: https://github.com/rust-lang/rust/pull/129466.
This commit is contained in:
bors 2024-09-13 03:47:30 +00:00
commit a5efa01895
29 changed files with 1393 additions and 35 deletions
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29
compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
View file

@ -1999,19 +1999,32 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
) {
let used_in_call = matches!(
explanation,
BorrowExplanation::UsedLater(LaterUseKind::Call | LaterUseKind::Other, _call_span, _)
BorrowExplanation::UsedLater(
_,
LaterUseKind::Call | LaterUseKind::Other,
_call_span,
_
)
);
if !used_in_call {
debug!("not later used in call");
return;
}
if matches!(
self.body.local_decls[issued_borrow.borrowed_place.local].local_info(),
LocalInfo::IfThenRescopeTemp { .. }
) {
// A better suggestion will be issued by the `if_let_rescope` lint
return;
}
let use_span =
if let BorrowExplanation::UsedLater(LaterUseKind::Other, use_span, _) = explanation {
Some(use_span)
} else {
None
};
let use_span = if let BorrowExplanation::UsedLater(_, LaterUseKind::Other, use_span, _) =
explanation
{
Some(use_span)
} else {
None
};
let outer_call_loc =
if let TwoPhaseActivation::ActivatedAt(loc) = issued_borrow.activation_location {
@ -2859,7 +2872,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
// and `move` will not help here.
(
Some(name),
BorrowExplanation::UsedLater(LaterUseKind::ClosureCapture, var_or_use_span, _),
BorrowExplanation::UsedLater(_, LaterUseKind::ClosureCapture, var_or_use_span, _),
) if borrow_spans.for_coroutine() || borrow_spans.for_closure() => self
.report_escaping_closure_capture(
borrow_spans,

110
compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs
View file

@ -30,7 +30,7 @@ use crate::{MirBorrowckCtxt, WriteKind};
#[derive(Debug)]
pub(crate) enum BorrowExplanation<'tcx> {
UsedLater(LaterUseKind, Span, Option<Span>),
UsedLater(Local, LaterUseKind, Span, Option<Span>),
UsedLaterInLoop(LaterUseKind, Span, Option<Span>),
UsedLaterWhenDropped {
drop_loc: Location,
@ -99,7 +99,12 @@ impl<'tcx> BorrowExplanation<'tcx> {
}
}
match *self {
BorrowExplanation::UsedLater(later_use_kind, var_or_use_span, path_span) => {
BorrowExplanation::UsedLater(
dropped_local,
later_use_kind,
var_or_use_span,
path_span,
) => {
let message = match later_use_kind {
LaterUseKind::TraitCapture => "captured here by trait object",
LaterUseKind::ClosureCapture => "captured here by closure",
@ -107,9 +112,26 @@ impl<'tcx> BorrowExplanation<'tcx> {
LaterUseKind::FakeLetRead => "stored here",
LaterUseKind::Other => "used here",
};
// We can use `var_or_use_span` if either `path_span` is not present, or both spans are the same
if path_span.map(|path_span| path_span == var_or_use_span).unwrap_or(true) {
if borrow_span.map(|sp| !sp.overlaps(var_or_use_span)).unwrap_or(true) {
let local_decl = &body.local_decls[dropped_local];
if let &LocalInfo::IfThenRescopeTemp { if_then } = local_decl.local_info()
&& let Some((_, hir::Node::Expr(expr))) = tcx.hir().parent_iter(if_then).next()
&& let hir::ExprKind::If(cond, conseq, alt) = expr.kind
&& let hir::ExprKind::Let(&hir::LetExpr {
span: _,
pat,
init,
// FIXME(#101728): enable rewrite when type ascription is stabilized again
ty: None,
recovered: _,
}) = cond.kind
&& pat.span.can_be_used_for_suggestions()
&& let Ok(pat) = tcx.sess.source_map().span_to_snippet(pat.span)
{
suggest_rewrite_if_let(tcx, expr, &pat, init, conseq, alt, err);
} else if path_span.map_or(true, |path_span| path_span == var_or_use_span) {
// We can use `var_or_use_span` if either `path_span` is not present, or both spans are the same
if borrow_span.map_or(true, |sp| !sp.overlaps(var_or_use_span)) {
err.span_label(
var_or_use_span,
format!("{borrow_desc}borrow later {message}"),
@ -255,6 +277,22 @@ impl<'tcx> BorrowExplanation<'tcx> {
Applicability::MaybeIncorrect,
);
};
} else if let &LocalInfo::IfThenRescopeTemp { if_then } =
local_decl.local_info()
&& let hir::Node::Expr(expr) = tcx.hir_node(if_then)
&& let hir::ExprKind::If(cond, conseq, alt) = expr.kind
&& let hir::ExprKind::Let(&hir::LetExpr {
span: _,
pat,
init,
// FIXME(#101728): enable rewrite when type ascription is stabilized again
ty: None,
recovered: _,
}) = cond.kind
&& pat.span.can_be_used_for_suggestions()
&& let Ok(pat) = tcx.sess.source_map().span_to_snippet(pat.span)
{
suggest_rewrite_if_let(tcx, expr, &pat, init, conseq, alt, err);
}
}
}
@ -390,6 +428,53 @@ impl<'tcx> BorrowExplanation<'tcx> {
}
}
fn suggest_rewrite_if_let(
tcx: TyCtxt<'_>,
expr: &hir::Expr<'_>,
pat: &str,
init: &hir::Expr<'_>,
conseq: &hir::Expr<'_>,
alt: Option<&hir::Expr<'_>>,
err: &mut Diag<'_>,
) {
let source_map = tcx.sess.source_map();
err.span_note(
source_map.end_point(conseq.span),
"lifetimes for temporaries generated in `if let`s have been shortened in Edition 2024 so that they are dropped here instead",
);
if expr.span.can_be_used_for_suggestions() && conseq.span.can_be_used_for_suggestions() {
let needs_block = if let Some(hir::Node::Expr(expr)) =
alt.and_then(|alt| tcx.hir().parent_iter(alt.hir_id).next()).map(|(_, node)| node)
{
matches!(expr.kind, hir::ExprKind::If(..))
} else {
false
};
let mut sugg = vec![
(
expr.span.shrink_to_lo().between(init.span),
if needs_block { "{ match ".into() } else { "match ".into() },
),
(conseq.span.shrink_to_lo(), format!(" {{ {pat} => ")),
];
let expr_end = expr.span.shrink_to_hi();
let mut expr_end_code;
if let Some(alt) = alt {
sugg.push((conseq.span.between(alt.span), " _ => ".into()));
expr_end_code = "}".to_string();
} else {
expr_end_code = " _ => {} }".into();
}
expr_end_code.push('}');
sugg.push((expr_end, expr_end_code));
err.multipart_suggestion(
"consider rewriting the `if` into `match` which preserves the extended lifetime",
sugg,
Applicability::MaybeIncorrect,
);
}
}
impl<'tcx> MirBorrowckCtxt<'_, '_, 'tcx> {
fn free_region_constraint_info(
&self,
@ -465,14 +550,21 @@ impl<'tcx> MirBorrowckCtxt<'_, '_, 'tcx> {
.or_else(|| self.borrow_spans(span, location));
if use_in_later_iteration_of_loop {
let later_use = self.later_use_kind(borrow, spans, use_location);
BorrowExplanation::UsedLaterInLoop(later_use.0, later_use.1, later_use.2)
let (later_use_kind, var_or_use_span, path_span) =
self.later_use_kind(borrow, spans, use_location);
BorrowExplanation::UsedLaterInLoop(later_use_kind, var_or_use_span, path_span)
} else {
// Check if the location represents a `FakeRead`, and adapt the error
// message to the `FakeReadCause` it is from: in particular,
// the ones inserted in optimized `let var = <expr>` patterns.
let later_use = self.later_use_kind(borrow, spans, location);
BorrowExplanation::UsedLater(later_use.0, later_use.1, later_use.2)
let (later_use_kind, var_or_use_span, path_span) =
self.later_use_kind(borrow, spans, location);
BorrowExplanation::UsedLater(
borrow.borrowed_place.local,
later_use_kind,
var_or_use_span,
path_span,
)
}
}

2
compiler/rustc_feature/src/unstable.rs
View file

@ -495,6 +495,8 @@ declare_features! (
(unstable, half_open_range_patterns_in_slices, "1.66.0", Some(67264)),
/// Allows `if let` guard in match arms.
(unstable, if_let_guard, "1.47.0", Some(51114)),
/// Rescoping temporaries in `if let` to align with Rust 2024.
(unstable, if_let_rescope, "CURRENT_RUSTC_VERSION", Some(124085)),
/// Allows `impl Trait` to be used inside associated types (RFC 2515).
(unstable, impl_trait_in_assoc_type, "1.70.0", Some(63063)),
/// Allows `impl Trait` as output type in `Fn` traits in return position of functions.

14
compiler/rustc_hir_analysis/src/check/region.rs
View file

@ -472,7 +472,12 @@ fn resolve_expr<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, expr: &'tcx h
hir::ExprKind::If(cond, then, Some(otherwise)) => {
let expr_cx = visitor.cx;
visitor.enter_scope(Scope { id: then.hir_id.local_id, data: ScopeData::IfThen });
let data = if expr.span.at_least_rust_2024() && visitor.tcx.features().if_let_rescope {
ScopeData::IfThenRescope
} else {
ScopeData::IfThen
};
visitor.enter_scope(Scope { id: then.hir_id.local_id, data });
visitor.cx.var_parent = visitor.cx.parent;
visitor.visit_expr(cond);
visitor.visit_expr(then);
@ -482,7 +487,12 @@ fn resolve_expr<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, expr: &'tcx h
hir::ExprKind::If(cond, then, None) => {
let expr_cx = visitor.cx;
visitor.enter_scope(Scope { id: then.hir_id.local_id, data: ScopeData::IfThen });
let data = if expr.span.at_least_rust_2024() && visitor.tcx.features().if_let_rescope {
ScopeData::IfThenRescope
} else {
ScopeData::IfThen
};
visitor.enter_scope(Scope { id: then.hir_id.local_id, data });
visitor.cx.var_parent = visitor.cx.parent;
visitor.visit_expr(cond);
visitor.visit_expr(then);

5
compiler/rustc_lint/messages.ftl
View file

@ -334,6 +334,11 @@ lint_identifier_uncommon_codepoints = identifier contains {$codepoints_len ->
*[other] {" "}{$identifier_type}
} Unicode general security profile
lint_if_let_rescope = `if let` assigns a shorter lifetime since Edition 2024
.label = this value has a significant drop implementation which may observe a major change in drop order and requires your discretion
.help = the value is now dropped here in Edition 2024
.suggestion = a `match` with a single arm can preserve the drop order up to Edition 2021
lint_ignored_unless_crate_specified = {$level}({$name}) is ignored unless specified at crate level
lint_ill_formed_attribute_input = {$num_suggestions ->

430
compiler/rustc_lint/src/if_let_rescope.rs Normal file
View file

@ -0,0 +1,430 @@
use std::iter::repeat;
use std::ops::ControlFlow;
use hir::intravisit::Visitor;
use rustc_ast::Recovered;
use rustc_errors::{
Applicability, Diag, EmissionGuarantee, SubdiagMessageOp, Subdiagnostic, SuggestionStyle,
};
use rustc_hir::{self as hir, HirIdSet};
use rustc_macros::LintDiagnostic;
use rustc_middle::ty::TyCtxt;
use rustc_session::lint::{FutureIncompatibilityReason, Level};
use rustc_session::{declare_lint, impl_lint_pass};
use rustc_span::edition::Edition;
use rustc_span::Span;
use crate::{LateContext, LateLintPass};
declare_lint! {
/// The `if_let_rescope` lint detects cases where a temporary value with
/// significant drop is generated on the right hand side of `if let`
/// and suggests a rewrite into `match` when possible.
///
/// ### Example
///
/// ```rust,edition2021
/// #![feature(if_let_rescope)]
/// #![warn(if_let_rescope)]
/// #![allow(unused_variables)]
///
/// struct Droppy;
/// impl Drop for Droppy {
/// fn drop(&mut self) {
/// // Custom destructor, including this `drop` implementation, is considered
/// // significant.
/// // Rust does not check whether this destructor emits side-effects that can
/// // lead to observable change in program semantics, when the drop order changes.
/// // Rust biases to be on the safe side, so that you can apply discretion whether
/// // this change indeed breaches any contract or specification that your code needs
/// // to honour.
/// println!("dropped");
/// }
/// }
/// impl Droppy {
/// fn get(&self) -> Option<u8> {
/// None
/// }
/// }
///
/// fn main() {
/// if let Some(value) = Droppy.get() {
/// // do something
/// } else {
/// // do something else
/// }
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// With Edition 2024, temporaries generated while evaluating `if let`s
/// will be dropped before the `else` block.
/// This lint captures a possible change in runtime behaviour due to
/// a change in sequence of calls to significant `Drop::drop` destructors.
///
/// A significant [`Drop::drop`](https://doc.rust-lang.org/std/ops/trait.Drop.html)
/// destructor here refers to an explicit, arbitrary implementation of the `Drop` trait on the type
/// with exceptions including `Vec`, `Box`, `Rc`, `BTreeMap` and `HashMap`
/// that are marked by the compiler otherwise so long that the generic types have
/// no significant destructor recursively.
/// In other words, a type has a significant drop destructor when it has a `Drop` implementation
/// or its destructor invokes a significant destructor on a type.
/// Since we cannot completely reason about the change by just inspecting the existence of
/// a significant destructor, this lint remains only a suggestion and is set to `allow` by default.
///
/// Whenever possible, a rewrite into an equivalent `match` expression that
/// observe the same order of calls to such destructors is proposed by this lint.
/// Authors may take their own discretion whether the rewrite suggestion shall be
/// accepted, or rejected to continue the use of the `if let` expression.
pub IF_LET_RESCOPE,
Allow,
"`if let` assigns a shorter lifetime to temporary values being pattern-matched against in Edition 2024 and \
rewriting in `match` is an option to preserve the semantics up to Edition 2021",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::EditionSemanticsChange(Edition::Edition2024),
reference: "issue #124085 <https://github.com/rust-lang/rust/issues/124085>",
};
}
/// Lint for potential change in program semantics of `if let`s
#[derive(Default)]
pub(crate) struct IfLetRescope {
skip: HirIdSet,
}
fn expr_parent_is_else(tcx: TyCtxt<'_>, hir_id: hir::HirId) -> bool {
let Some((_, hir::Node::Expr(expr))) = tcx.hir().parent_iter(hir_id).next() else {
return false;
};
let hir::ExprKind::If(_cond, _conseq, Some(alt)) = expr.kind else { return false };
alt.hir_id == hir_id
}
fn expr_parent_is_stmt(tcx: TyCtxt<'_>, hir_id: hir::HirId) -> bool {
let Some((_, hir::Node::Stmt(stmt))) = tcx.hir().parent_iter(hir_id).next() else {
return false;
};
let (hir::StmtKind::Semi(expr) | hir::StmtKind::Expr(expr)) = stmt.kind else { return false };
expr.hir_id == hir_id
}
fn match_head_needs_bracket(tcx: TyCtxt<'_>, expr: &hir::Expr<'_>) -> bool {
expr_parent_is_else(tcx, expr.hir_id) && matches!(expr.kind, hir::ExprKind::If(..))
}
impl IfLetRescope {
fn probe_if_cascade<'tcx>(&mut self, cx: &LateContext<'tcx>, mut expr: &'tcx hir::Expr<'tcx>) {
if self.skip.contains(&expr.hir_id) {
return;
}
let tcx = cx.tcx;
let source_map = tcx.sess.source_map();
let expr_end = expr.span.shrink_to_hi();
let mut add_bracket_to_match_head = match_head_needs_bracket(tcx, expr);
let mut significant_droppers = vec![];
let mut lifetime_ends = vec![];
let mut closing_brackets = 0;
let mut alt_heads = vec![];
let mut match_heads = vec![];
let mut consequent_heads = vec![];
let mut first_if_to_lint = None;
let mut first_if_to_rewrite = false;
let mut empty_alt = false;
while let hir::ExprKind::If(cond, conseq, alt) = expr.kind {
self.skip.insert(expr.hir_id);
// We are interested in `let` fragment of the condition.
// Otherwise, we probe into the `else` fragment.
if let hir::ExprKind::Let(&hir::LetExpr {
span,
pat,
init,
ty: ty_ascription,
recovered: Recovered::No,
}) = cond.kind
{
let if_let_pat = expr.span.shrink_to_lo().between(init.span);
// The consequent fragment is always a block.
let before_conseq = conseq.span.shrink_to_lo();
let lifetime_end = source_map.end_point(conseq.span);
if let ControlFlow::Break(significant_dropper) =
(FindSignificantDropper { cx }).visit_expr(init)
{
first_if_to_lint = first_if_to_lint.or_else(|| Some((span, expr.hir_id)));
significant_droppers.push(significant_dropper);
lifetime_ends.push(lifetime_end);
if ty_ascription.is_some()
|| !expr.span.can_be_used_for_suggestions()
|| !pat.span.can_be_used_for_suggestions()
{
// Our `match` rewrites does not support type ascription,
// so we just bail.
// Alternatively when the span comes from proc macro expansion,
// we will also bail.
// FIXME(#101728): change this when type ascription syntax is stabilized again
} else if let Ok(pat) = source_map.span_to_snippet(pat.span) {
let emit_suggestion = |alt_span| {
first_if_to_rewrite = true;
if add_bracket_to_match_head {
closing_brackets += 2;
match_heads.push(SingleArmMatchBegin::WithOpenBracket(if_let_pat));
} else {
// Sometimes, wrapping `match` into a block is undesirable,
// because the scrutinee temporary lifetime is shortened and
// the proposed fix will not work.
closing_brackets += 1;
match_heads
.push(SingleArmMatchBegin::WithoutOpenBracket(if_let_pat));
}
consequent_heads.push(ConsequentRewrite { span: before_conseq, pat });
if let Some(alt_span) = alt_span {
alt_heads.push(AltHead(alt_span));
}
};
if let Some(alt) = alt {
let alt_head = conseq.span.between(alt.span);
if alt_head.can_be_used_for_suggestions() {
// We lint only when the `else` span is user code, too.
emit_suggestion(Some(alt_head));
}
} else {
// This is the end of the `if .. else ..` cascade.
// We can stop here.
emit_suggestion(None);
empty_alt = true;
break;
}
}
}
}
// At this point, any `if let` fragment in the cascade is definitely preceeded by `else`,
// so a opening bracket is mandatory before each `match`.
add_bracket_to_match_head = true;
if let Some(alt) = alt {
expr = alt;
} else {
break;
}
}
if let Some((span, hir_id)) = first_if_to_lint {
tcx.emit_node_span_lint(
IF_LET_RESCOPE,
hir_id,
span,
IfLetRescopeLint {
significant_droppers,
lifetime_ends,
rewrite: first_if_to_rewrite.then_some(IfLetRescopeRewrite {
match_heads,
consequent_heads,
closing_brackets: ClosingBrackets {
span: expr_end,
count: closing_brackets,
empty_alt,
},
alt_heads,
}),
},
);
}
}
}
impl_lint_pass!(
IfLetRescope => [IF_LET_RESCOPE]
);
impl<'tcx> LateLintPass<'tcx> for IfLetRescope {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
if expr.span.edition().at_least_rust_2024() || !cx.tcx.features().if_let_rescope {
return;
}
if let (Level::Allow, _) = cx.tcx.lint_level_at_node(IF_LET_RESCOPE, expr.hir_id) {
return;
}
if expr_parent_is_stmt(cx.tcx, expr.hir_id)
&& matches!(expr.kind, hir::ExprKind::If(_cond, _conseq, None))
{
// `if let` statement without an `else` branch has no observable change
// so we can skip linting it
return;
}
self.probe_if_cascade(cx, expr);
}
}
#[derive(LintDiagnostic)]
#[diag(lint_if_let_rescope)]
struct IfLetRescopeLint {
#[label]
significant_droppers: Vec<Span>,
#[help]
lifetime_ends: Vec<Span>,
#[subdiagnostic]
rewrite: Option<IfLetRescopeRewrite>,
}
// #[derive(Subdiagnostic)]
struct IfLetRescopeRewrite {
match_heads: Vec<SingleArmMatchBegin>,
consequent_heads: Vec<ConsequentRewrite>,
closing_brackets: ClosingBrackets,
alt_heads: Vec<AltHead>,
}
impl Subdiagnostic for IfLetRescopeRewrite {
fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
self,
diag: &mut Diag<'_, G>,
f: &F,
) {
let mut suggestions = vec![];
for match_head in self.match_heads {
match match_head {
SingleArmMatchBegin::WithOpenBracket(span) => {
suggestions.push((span, "{ match ".into()))
}
SingleArmMatchBegin::WithoutOpenBracket(span) => {
suggestions.push((span, "match ".into()))
}
}
}
for ConsequentRewrite { span, pat } in self.consequent_heads {
suggestions.push((span, format!("{{ {pat} => ")));
}
for AltHead(span) in self.alt_heads {
suggestions.push((span, " _ => ".into()));
}
let closing_brackets = self.closing_brackets;
suggestions.push((
closing_brackets.span,
closing_brackets
.empty_alt
.then_some(" _ => {}".chars())
.into_iter()
.flatten()
.chain(repeat('}').take(closing_brackets.count))
.collect(),
));
let msg = f(diag, crate::fluent_generated::lint_suggestion.into());
diag.multipart_suggestion_with_style(
msg,
suggestions,
Applicability::MachineApplicable,
SuggestionStyle::ShowCode,
);
}
}
struct AltHead(Span);
struct ConsequentRewrite {
span: Span,
pat: String,
}
struct ClosingBrackets {
span: Span,
count: usize,
empty_alt: bool,
}
enum SingleArmMatchBegin {
WithOpenBracket(Span),
WithoutOpenBracket(Span),
}
struct FindSignificantDropper<'tcx, 'a> {
cx: &'a LateContext<'tcx>,
}
impl<'tcx, 'a> Visitor<'tcx> for FindSignificantDropper<'tcx, 'a> {
type Result = ControlFlow<Span>;
fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) -> Self::Result {
if self
.cx
.typeck_results()
.expr_ty(expr)
.has_significant_drop(self.cx.tcx, self.cx.param_env)
{
return ControlFlow::Break(expr.span);
}
match expr.kind {
hir::ExprKind::ConstBlock(_)
| hir::ExprKind::Lit(_)
| hir::ExprKind::Path(_)
| hir::ExprKind::Assign(_, _, _)
| hir::ExprKind::AssignOp(_, _, _)
| hir::ExprKind::Break(_, _)
| hir::ExprKind::Continue(_)
| hir::ExprKind::Ret(_)
| hir::ExprKind::Become(_)
| hir::ExprKind::InlineAsm(_)
| hir::ExprKind::OffsetOf(_, _)
| hir::ExprKind::Repeat(_, _)
| hir::ExprKind::Err(_)
| hir::ExprKind::Struct(_, _, _)
| hir::ExprKind::Closure(_)
| hir::ExprKind::Block(_, _)
| hir::ExprKind::DropTemps(_)
| hir::ExprKind::Loop(_, _, _, _) => ControlFlow::Continue(()),
hir::ExprKind::Tup(exprs) | hir::ExprKind::Array(exprs) => {
for expr in exprs {
self.visit_expr(expr)?;
}
ControlFlow::Continue(())
}
hir::ExprKind::Call(callee, args) => {
self.visit_expr(callee)?;
for expr in args {
self.visit_expr(expr)?;
}
ControlFlow::Continue(())
}
hir::ExprKind::MethodCall(_, receiver, args, _) => {
self.visit_expr(receiver)?;
for expr in args {
self.visit_expr(expr)?;
}
ControlFlow::Continue(())
}
hir::ExprKind::Index(left, right, _) | hir::ExprKind::Binary(_, left, right) => {
self.visit_expr(left)?;
self.visit_expr(right)
}
hir::ExprKind::Unary(_, expr)
| hir::ExprKind::Cast(expr, _)
| hir::ExprKind::Type(expr, _)
| hir::ExprKind::Yield(expr, _)
| hir::ExprKind::AddrOf(_, _, expr)
| hir::ExprKind::Match(expr, _, _)
| hir::ExprKind::Field(expr, _)
| hir::ExprKind::Let(&hir::LetExpr {
init: expr,
span: _,
pat: _,
ty: _,
recovered: Recovered::No,
}) => self.visit_expr(expr),
hir::ExprKind::Let(_) => ControlFlow::Continue(()),
hir::ExprKind::If(cond, _, _) => {
if let hir::ExprKind::Let(hir::LetExpr {
init,
span: _,
pat: _,
ty: _,
recovered: Recovered::No,
}) = cond.kind
{
self.visit_expr(init)?;
}
ControlFlow::Continue(())
}
}
}
}

3
compiler/rustc_lint/src/lib.rs
View file

@ -56,6 +56,7 @@ mod expect;
mod for_loops_over_fallibles;
mod foreign_modules;
pub mod hidden_unicode_codepoints;
mod if_let_rescope;
mod impl_trait_overcaptures;
mod internal;
mod invalid_from_utf8;
@ -94,6 +95,7 @@ use drop_forget_useless::*;
use enum_intrinsics_non_enums::EnumIntrinsicsNonEnums;
use for_loops_over_fallibles::*;
use hidden_unicode_codepoints::*;
use if_let_rescope::IfLetRescope;
use impl_trait_overcaptures::ImplTraitOvercaptures;
use internal::*;
use invalid_from_utf8::*;
@ -243,6 +245,7 @@ late_lint_methods!(
NonLocalDefinitions: NonLocalDefinitions::default(),
ImplTraitOvercaptures: ImplTraitOvercaptures,
TailExprDropOrder: TailExprDropOrder,
IfLetRescope: IfLetRescope::default(),
]
]
);

6
compiler/rustc_middle/src/middle/region.rs
View file

@ -96,6 +96,7 @@ impl fmt::Debug for Scope {
ScopeData::Arguments => write!(fmt, "Arguments({:?})", self.id),
ScopeData::Destruction => write!(fmt, "Destruction({:?})", self.id),
ScopeData::IfThen => write!(fmt, "IfThen({:?})", self.id),
ScopeData::IfThenRescope => write!(fmt, "IfThen[edition2024]({:?})", self.id),
ScopeData::Remainder(fsi) => write!(
fmt,
"Remainder {{ block: {:?}, first_statement_index: {}}}",
@ -126,6 +127,11 @@ pub enum ScopeData {
/// Used for variables introduced in an if-let expression.
IfThen,
/// Scope of the condition and then block of an if expression
/// Used for variables introduced in an if-let expression,
/// whose lifetimes do not cross beyond this scope.
IfThenRescope,
/// Scope following a `let id = expr;` binding in a block.
Remainder(FirstStatementIndex),
}

3
compiler/rustc_middle/src/mir/mod.rs
View file

@ -1084,6 +1084,9 @@ pub enum LocalInfo<'tcx> {
/// (with no intervening statement context).
// FIXME(matthewjasper) Don't store in this in `Body`
BlockTailTemp(BlockTailInfo),
/// A temporary created during evaluating `if` predicate, possibly for pattern matching for `let`s,
/// and subject to Edition 2024 temporary lifetime rules
IfThenRescopeTemp { if_then: HirId },
/// A temporary created during the pass `Derefer` to avoid it's retagging
DerefTemp,
/// A temporary created for borrow checking.

10
compiler/rustc_middle/src/ty/rvalue_scopes.rs
View file

@ -41,7 +41,15 @@ impl RvalueScopes {
debug!("temporary_scope({expr_id:?}) = {id:?} [enclosing]");
return Some(id);
}
_ => id = p,
ScopeData::IfThenRescope => {
debug!("temporary_scope({expr_id:?}) = {p:?} [enclosing]");
return Some(p);
}
ScopeData::Node
| ScopeData::CallSite
| ScopeData::Arguments
| ScopeData::IfThen
| ScopeData::Remainder(_) => id = p,
}
}

10
compiler/rustc_mir_build/src/build/expr/as_temp.rs
View file

@ -1,7 +1,9 @@
//! See docs in build/expr/mod.rs
use rustc_data_structures::stack::ensure_sufficient_stack;
use rustc_hir::HirId;
use rustc_middle::middle::region;
use rustc_middle::middle::region::{Scope, ScopeData};
use rustc_middle::mir::*;
use rustc_middle::thir::*;
use tracing::{debug, instrument};
@ -73,11 +75,19 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
_ if let Some(tail_info) = this.block_context.currently_in_block_tail() => {
LocalInfo::BlockTailTemp(tail_info)
}
_ if let Some(Scope { data: ScopeData::IfThenRescope, id }) = temp_lifetime => {
LocalInfo::IfThenRescopeTemp {
if_then: HirId { owner: this.hir_id.owner, local_id: id },
}
}
_ => LocalInfo::Boring,
};
**local_decl.local_info.as_mut().assert_crate_local() = local_info;
this.local_decls.push(local_decl)
};
debug!(?temp);
if deduplicate_temps {
this.fixed_temps.insert(expr_id, temp);
}

8
compiler/rustc_mir_build/src/thir/cx/expr.rs
View file

@ -706,7 +706,13 @@ impl<'tcx> Cx<'tcx> {
hir::ExprKind::If(cond, then, else_opt) => ExprKind::If {
if_then_scope: region::Scope {
id: then.hir_id.local_id,
data: region::ScopeData::IfThen,
data: {
if expr.span.at_least_rust_2024() && tcx.features().if_let_rescope {
region::ScopeData::IfThenRescope
} else {
region::ScopeData::IfThen
}
},
},
cond: self.mirror_expr(cond),
then: self.mirror_expr(then),

1
compiler/rustc_span/src/symbol.rs
View file

@ -1016,6 +1016,7 @@ symbols! {
ident,
if_let,
if_let_guard,
if_let_rescope,
if_while_or_patterns,
ignore,
impl_header_lifetime_elision,