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Introduce terminating scope for tail expressions of breakable scopes #106493

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Introduce terminating scope for tail expressions of breakable scopes #106493

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7 changes: 7 additions & 0 deletions compiler/rustc_hir_analysis/src/check/region.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -166,6 +166,13 @@ fn resolve_block<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, blk: &'tcx h
hir::StmtKind::Expr(..) | hir::StmtKind::Semi(..) => visitor.visit_stmt(statement),
}
}

// We must introduce a terminating scope for tail expressions in breakable
// scopes, otherwise incorrect drops and unwind paths are created, see #104736.
if blk.targeted_by_break && let Some(expr) = blk.expr {
visitor.terminating_scopes.insert(expr.hir_id.local_id);
}

walk_list!(visitor, visit_expr, &blk.expr);
}

Expand Down
36 changes: 36 additions & 0 deletions src/test/mir-opt/building/breakable_scope_drops.rs
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// EMIT_MIR breakable_scope_drops.weird_temporary.built.after.mir

struct A;
struct B;

impl Drop for A {
fn drop(&mut self) {}
}
impl Drop for B {
fn drop(&mut self) {}
}

#[inline(always)]
fn no_unwind() {}


fn weird_temporary(a: A, b: B, nothing: ((), (), ()), x: bool) -> ((), (), ()) {
let _temp = 'scope: {
(
{
let _z = b;
if x {
break 'scope nothing;
}
},
match { a } {
_ => (),
},
no_unwind(),
)
};

nothing
}

fn main() {}
134 changes: 134 additions & 0 deletions src/test/mir-opt/building/breakable_scope_drops.weird_temporary.built.after.mir
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// MIR for `weird_temporary` after built

fn weird_temporary(_1: A, _2: B, _3: ((), (), ()), _4: bool) -> ((), (), ()) {
debug a => _1; // in scope 0 at $DIR/breakable-scope-drops.rs:+0:20: +0:21
debug b => _2; // in scope 0 at $DIR/breakable-scope-drops.rs:+0:26: +0:27
debug nothing => _3; // in scope 0 at $DIR/breakable-scope-drops.rs:+0:32: +0:39
debug x => _4; // in scope 0 at $DIR/breakable-scope-drops.rs:+0:55: +0:56
let mut _0: ((), (), ()); // return place in scope 0 at $DIR/breakable-scope-drops.rs:+0:67: +0:79
let _5: ((), (), ()); // in scope 0 at $DIR/breakable-scope-drops.rs:+1:9: +1:14
let mut _6: (); // in scope 0 at $DIR/breakable-scope-drops.rs:+3:13: +8:14
let _7: B; // in scope 0 at $DIR/breakable-scope-drops.rs:+4:21: +4:23
let mut _8: bool; // in scope 0 at $DIR/breakable-scope-drops.rs:+5:20: +5:21
let mut _9: !; // in scope 0 at $DIR/breakable-scope-drops.rs:+5:22: +7:18
let mut _10: (); // in scope 0 at $DIR/breakable-scope-drops.rs:+9:13: +11:14
let mut _11: A; // in scope 0 at $DIR/breakable-scope-drops.rs:+9:19: +9:24
let mut _12: (); // in scope 0 at $DIR/breakable-scope-drops.rs:+12:13: +12:24
scope 1 {
debug _temp => _5; // in scope 1 at $DIR/breakable-scope-drops.rs:+1:9: +1:14
}
scope 2 {
debug _z => _7; // in scope 2 at $DIR/breakable-scope-drops.rs:+4:21: +4:23
}

bb0: {
StorageLive(_5); // scope 0 at $DIR/breakable-scope-drops.rs:+1:9: +1:14
StorageLive(_6); // scope 0 at $DIR/breakable-scope-drops.rs:+3:13: +8:14
StorageLive(_7); // scope 0 at $DIR/breakable-scope-drops.rs:+4:21: +4:23
_7 = move _2; // scope 0 at $DIR/breakable-scope-drops.rs:+4:26: +4:27
FakeRead(ForLet(None), _7); // scope 0 at $DIR/breakable-scope-drops.rs:+4:21: +4:23
StorageLive(_8); // scope 2 at $DIR/breakable-scope-drops.rs:+5:20: +5:21
_8 = _4; // scope 2 at $DIR/breakable-scope-drops.rs:+5:20: +5:21
switchInt(move _8) -> [0: bb2, otherwise: bb1]; // scope 2 at $DIR/breakable-scope-drops.rs:+5:20: +5:21
}

bb1: {
_5 = _3; // scope 2 at $DIR/breakable-scope-drops.rs:+6:34: +6:41
goto -> bb11; // scope 2 at $DIR/breakable-scope-drops.rs:+6:21: +6:41
}

bb2: {
goto -> bb5; // scope 2 at $DIR/breakable-scope-drops.rs:+5:20: +5:21
}

bb3: {
unreachable; // scope 2 at $DIR/breakable-scope-drops.rs:+5:22: +7:18
}

bb4: {
goto -> bb6; // scope 2 at $DIR/breakable-scope-drops.rs:+5:17: +7:18
}

bb5: {
_6 = const (); // scope 2 at $DIR/breakable-scope-drops.rs:+7:18: +7:18
goto -> bb6; // scope 2 at $DIR/breakable-scope-drops.rs:+5:17: +7:18
}

bb6: {
StorageDead(_8); // scope 2 at $DIR/breakable-scope-drops.rs:+7:17: +7:18
drop(_7) -> [return: bb7, unwind: bb17]; // scope 0 at $DIR/breakable-scope-drops.rs:+8:13: +8:14
}

bb7: {
StorageDead(_7); // scope 0 at $DIR/breakable-scope-drops.rs:+8:13: +8:14
StorageLive(_10); // scope 0 at $DIR/breakable-scope-drops.rs:+9:13: +11:14
StorageLive(_11); // scope 0 at $DIR/breakable-scope-drops.rs:+9:19: +9:24
_11 = move _1; // scope 0 at $DIR/breakable-scope-drops.rs:+9:21: +9:22
FakeRead(ForMatchedPlace(None), _11); // scope 0 at $DIR/breakable-scope-drops.rs:+9:19: +9:24
_10 = (); // scope 0 at $DIR/breakable-scope-drops.rs:+10:22: +10:24
goto -> bb8; // scope 0 at $DIR/breakable-scope-drops.rs:+10:22: +10:24
}

bb8: {
StorageLive(_12); // scope 0 at $DIR/breakable-scope-drops.rs:+12:13: +12:24
_12 = no_unwind() -> [return: bb9, unwind: bb16]; // scope 0 at $DIR/breakable-scope-drops.rs:+12:13: +12:24
// mir::Constant
// + span: $DIR/breakable-scope-drops.rs:29:13: 29:22
// + literal: Const { ty: fn() {no_unwind}, val: Value(<ZST>) }
}

bb9: {
_5 = (move _6, move _10, move _12); // scope 0 at $DIR/breakable-scope-drops.rs:+2:9: +13:10
StorageDead(_12); // scope 0 at $DIR/breakable-scope-drops.rs:+13:9: +13:10
drop(_11) -> [return: bb10, unwind: bb17]; // scope 0 at $DIR/breakable-scope-drops.rs:+13:9: +13:10
}

bb10: {
StorageDead(_11); // scope 0 at $DIR/breakable-scope-drops.rs:+13:9: +13:10
StorageDead(_10); // scope 0 at $DIR/breakable-scope-drops.rs:+13:9: +13:10
StorageDead(_6); // scope 0 at $DIR/breakable-scope-drops.rs:+13:9: +13:10
goto -> bb13; // scope 0 at $DIR/breakable-scope-drops.rs:+1:17: +14:6
}

bb11: {
StorageDead(_8); // scope 2 at $DIR/breakable-scope-drops.rs:+7:17: +7:18
drop(_7) -> [return: bb12, unwind: bb17]; // scope 0 at $DIR/breakable-scope-drops.rs:+8:13: +8:14
}

bb12: {
StorageDead(_7); // scope 0 at $DIR/breakable-scope-drops.rs:+8:13: +8:14
StorageDead(_6); // scope 0 at $DIR/breakable-scope-drops.rs:+13:9: +13:10
goto -> bb13; // scope 0 at $DIR/breakable-scope-drops.rs:+1:17: +14:6
}

bb13: {
FakeRead(ForLet(None), _5); // scope 0 at $DIR/breakable-scope-drops.rs:+1:9: +1:14
_0 = _3; // scope 1 at $DIR/breakable-scope-drops.rs:+16:5: +16:12
StorageDead(_5); // scope 0 at $DIR/breakable-scope-drops.rs:+17:1: +17:2
drop(_2) -> [return: bb14, unwind: bb18]; // scope 0 at $DIR/breakable-scope-drops.rs:+17:1: +17:2
}

bb14: {
drop(_1) -> [return: bb15, unwind: bb19]; // scope 0 at $DIR/breakable-scope-drops.rs:+17:1: +17:2
}

bb15: {
return; // scope 0 at $DIR/breakable-scope-drops.rs:+17:2: +17:2
}

bb16 (cleanup): {
drop(_11) -> bb17; // scope 0 at $DIR/breakable-scope-drops.rs:+13:9: +13:10
}

bb17 (cleanup): {
drop(_2) -> bb18; // scope 0 at $DIR/breakable-scope-drops.rs:+17:1: +17:2
}

bb18 (cleanup): {
drop(_1) -> bb19; // scope 0 at $DIR/breakable-scope-drops.rs:+17:1: +17:2
}

bb19 (cleanup): {
resume; // scope 0 at $DIR/breakable-scope-drops.rs:+0:1: +17:2
}
}
24 changes: 24 additions & 0 deletions src/test/ui/borrowck/tail-expression-breakable-scope.rs
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struct A;

impl Drop for A {
fn drop(&mut self) {}
}

fn takes_a_ref<'a>(_arg: &'a A) {}

fn returns_a() -> A {
A
}

fn weird_temporary<'a>(a: &'a A, x: bool) {
takes_a_ref('scope: {
if x {
break 'scope a;
}

&returns_a()
//~^ ERROR temporary value dropped while borrowed
});
}

fn main() {}
15 changes: 15 additions & 0 deletions src/test/ui/borrowck/tail-expression-breakable-scope.stderr
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error[E0716]: temporary value dropped while borrowed
--> $DIR/tail-expression-breakable-scope.rs:19:10
|
LL | &returns_a()
| -^^^^^^^^^^-
| || |
| || temporary value is freed at the end of this statement
| |creates a temporary value which is freed while still in use
| borrow later used here
|
= note: consider using a `let` binding to create a longer lived value

error: aborting due to previous error

For more information about this error, try `rustc --explain E0716`.
20 changes: 20 additions & 0 deletions src/test/ui/try-block/dot-dot.rs
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// compile-flags: --crate-type=lib -Copt-level=3 -Zvalidate-mir --edition=2021
// build-pass

#![feature(try_blocks)]

#[derive(Default, Debug)]
struct Response {
bookmarks: String,
continue_after: String,
}

fn format_response(page: Result<String, String>) -> Result<Response, String> {
try {
Response {
bookmarks: String::new(),
continue_after: page?,
..Default::default()
}
}
}