Auto merge of rust-lang#134523 - dingxiangfei2009:issue-130836-attemp…

…t-2, r=<try> Run borrowck tests on BIDs and emit tail-expr-drop-order lints for violations Fix rust-lang#132861 r? `@nikomatsakis` cc `@compiler-errors` This patch enlarges the scope where the `tail-expr-drop-order` lint applies, so that all locals involved in tail expressions are inspected. This is necessary to run borrow-checking to capture the cases where it used to compile under Edition 2021 but is not going to pass borrow-checking from Edition 2024 onwards. The way it works is to inspect each BID against the set of borrows that are still live. If the local involved in BID has a borrow index which happens to be live as well at the location of this BID statement, in the future this will be a borrow-checking violation. The lint will fire in this case.
rust-lang-ci · Jan 5, 2025 · 214d5c9 · 214d5c9
2 parents dcfa38f + 4749325
commit 214d5c9
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diff --git a/compiler/rustc_borrowck/messages.ftl b/compiler/rustc_borrowck/messages.ftl
@@ -213,6 +213,9 @@ borrowck_suggest_create_fresh_reborrow =
 borrowck_suggest_iterate_over_slice =
     consider iterating over a slice of the `{$ty}`'s content to avoid moving into the `for` loop
 
+borrowck_tail_expr_drop_order = a temporary value will be dropped here before the execution exits the block in Edition 2024, which will raise borrow checking error
+    .label = consider using a `let` binding to create a longer lived value; or replacing the `{"{"} .. {"}"}` block with curly brackets `( .. )`; or folding the rest of the expression into the surrounding `unsafe {"{"} .. {"}"}`
+
 borrowck_ty_no_impl_copy =
     {$is_partial_move ->
         [true] partial move

diff --git a/compiler/rustc_borrowck/src/lib.rs b/compiler/rustc_borrowck/src/lib.rs
@@ -15,6 +15,7 @@
 #![warn(unreachable_pub)]
 // tidy-alphabetical-end
 
+use std::borrow::Cow;
 use std::cell::RefCell;
 use std::marker::PhantomData;
 use std::ops::Deref;
@@ -23,6 +24,7 @@ use rustc_abi::FieldIdx;
 use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
 use rustc_data_structures::graph::dominators::Dominators;
 use rustc_hir as hir;
+use rustc_hir::CRATE_HIR_ID;
 use rustc_hir::def_id::LocalDefId;
 use rustc_index::bit_set::{BitSet, MixedBitSet};
 use rustc_index::{IndexSlice, IndexVec};
@@ -42,7 +44,7 @@ use rustc_mir_dataflow::move_paths::{
     InitIndex, InitLocation, LookupResult, MoveData, MovePathIndex,
 };
 use rustc_mir_dataflow::{Analysis, EntryStates, Results, ResultsVisitor, visit_results};
-use rustc_session::lint::builtin::UNUSED_MUT;
+use rustc_session::lint::builtin::{TAIL_EXPR_DROP_ORDER, UNUSED_MUT};
 use rustc_span::{Span, Symbol};
 use smallvec::SmallVec;
 use tracing::{debug, instrument};
@@ -636,9 +638,11 @@ impl<'a, 'tcx> ResultsVisitor<'a, 'tcx, Borrowck<'a, 'tcx>> for MirBorrowckCtxt<
             | StatementKind::Coverage(..)
             // These do not actually affect borrowck
             | StatementKind::ConstEvalCounter
-            // This do not affect borrowck
-            | StatementKind::BackwardIncompatibleDropHint { .. }
             | StatementKind::StorageLive(..) => {}
+            // This does not affect borrowck
+            StatementKind::BackwardIncompatibleDropHint { place, reason: BackwardIncompatibleDropReason::Edition2024 } => {
+                self.check_backward_incompatible_drop(location, (**place, span), state);
+            }
             StatementKind::StorageDead(local) => {
                 self.access_place(
                     location,
@@ -1007,6 +1011,24 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, '_, 'tcx> {
         }
     }
 
+    fn borrows_in_scope<'s>(
+        &self,
+        location: Location,
+        state: &'s BorrowckDomain,
+    ) -> Cow<'s, BitSet<BorrowIndex>> {
+        if let Some(polonius) = &self.polonius_output {
+            // Use polonius output if it has been enabled.
+            let location = self.location_table.start_index(location);
+            let mut polonius_output = BitSet::new_empty(self.borrow_set.len());
+            for &idx in polonius.errors_at(location) {
+                polonius_output.insert(idx);
+            }
+            Cow::Owned(polonius_output)
+        } else {
+            Cow::Borrowed(&state.borrows)
+        }
+    }
+
     #[instrument(level = "debug", skip(self, state))]
     fn check_access_for_conflict(
         &mut self,
@@ -1018,18 +1040,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, '_, 'tcx> {
     ) -> bool {
         let mut error_reported = false;
 
-        // Use polonius output if it has been enabled.
-        let mut polonius_output;
-        let borrows_in_scope = if let Some(polonius) = &self.polonius_output {
-            let location = self.location_table.start_index(location);
-            polonius_output = BitSet::new_empty(self.borrow_set.len());
-            for &idx in polonius.errors_at(location) {
-                polonius_output.insert(idx);
-            }
-            &polonius_output
-        } else {
-            &state.borrows
-        };
+        let borrows_in_scope = self.borrows_in_scope(location, state);
 
         each_borrow_involving_path(
             self,
@@ -1149,6 +1160,53 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, '_, 'tcx> {
         error_reported
     }
 
+    /// Through #123739, backward incompatible drops (BIDs) are introduced.
+    /// We would like to emit lints whether borrow checking fails at these future drop locations.
+    #[instrument(level = "debug", skip(self, state))]
+    fn check_backward_incompatible_drop(
+        &mut self,
+        location: Location,
+        (place, place_span): (Place<'tcx>, Span),
+        state: &BorrowckDomain,
+    ) {
+        let tcx = self.infcx.tcx;
+        // If this type does not need `Drop`, then treat it like a `StorageDead`.
+        // This is needed because we track the borrows of refs to thread locals,
+        // and we'll ICE because we don't track borrows behind shared references.
+        let sd = if place.ty(self.body, tcx).ty.needs_drop(tcx, self.body.typing_env(tcx)) {
+            AccessDepth::Drop
+        } else {
+            AccessDepth::Shallow(None)
+        };
+
+        let borrows_in_scope = self.borrows_in_scope(location, state);
+
+        // This is a very simplified version of `Self::check_access_for_conflict`.
+        // We are here checking on BIDs and specifically still-live borrows of data involving the BIDs.
+        each_borrow_involving_path(
+            self,
+            self.infcx.tcx,
+            self.body,
+            (sd, place),
+            self.borrow_set,
+            |borrow_index| borrows_in_scope.contains(borrow_index),
+            |this, _borrow_index, borrow| {
+                if matches!(borrow.kind, BorrowKind::Fake(_)) {
+                    return Control::Continue;
+                }
+                let borrowed = this.retrieve_borrow_spans(borrow).var_or_use_path_span();
+                this.infcx.tcx.emit_node_span_lint(
+                    TAIL_EXPR_DROP_ORDER,
+                    CRATE_HIR_ID,
+                    place_span,
+                    session_diagnostics::TailExprDropOrder { borrowed },
+                );
+                // We may stop at the first case
+                Control::Break
+            },
+        );
+    }
+
     fn mutate_place(
         &mut self,
         location: Location,

diff --git a/compiler/rustc_borrowck/src/session_diagnostics.rs b/compiler/rustc_borrowck/src/session_diagnostics.rs
@@ -480,3 +480,10 @@ pub(crate) struct SimdIntrinsicArgConst {
     pub arg: usize,
     pub intrinsic: String,
 }
+
+#[derive(LintDiagnostic)]
+#[diag(borrowck_tail_expr_drop_order)]
+pub(crate) struct TailExprDropOrder {
+    #[label]
+    pub borrowed: Span,
+}
diff --git a/compiler/rustc_mir_build/src/builder/scope.rs b/compiler/rustc_mir_build/src/builder/scope.rs
@@ -1131,15 +1131,15 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
     /// Schedule emission of a backwards incompatible drop lint hint.
     /// Applicable only to temporary values for now.
+    #[instrument(level = "debug", skip(self))]
     pub(crate) fn schedule_backwards_incompatible_drop(
         &mut self,
         span: Span,
         region_scope: region::Scope,
         local: Local,
     ) {
-        if !self.local_decls[local].ty.has_significant_drop(self.tcx, self.typing_env()) {
-            return;
-        }
+        // Note that we are *not* gating BIDs here on whether they have significant destructor.
+        // We need to know all of them so that we can capture potential borrow-checking errors.
         for scope in self.scopes.scopes.iter_mut().rev() {
             // Since we are inserting linting MIR statement, we have to invalidate the caches
             scope.invalidate_cache();

diff --git a/compiler/rustc_mir_transform/src/lint_tail_expr_drop_order.rs b/compiler/rustc_mir_transform/src/lint_tail_expr_drop_order.rs
@@ -351,14 +351,19 @@ pub(crate) fn run_lint<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId, body: &Body<
     {
         return;
     }
+
+    // FIXME(typing_env): This should be able to reveal the opaques local to the
+    // body using the typeck results.
+    let typing_env = ty::TypingEnv::non_body_analysis(tcx, def_id);
+
     // ## About BIDs in blocks ##
     // Track the set of blocks that contain a backwards-incompatible drop (BID)
     // and, for each block, the vector of locations.
     //
     // We group them per-block because they tend to scheduled in the same drop ladder block.
     let mut bid_per_block = IndexMap::default();
     let mut bid_places = UnordSet::new();
-    let typing_env = ty::TypingEnv::post_analysis(tcx, def_id);
+
     let mut ty_dropped_components = UnordMap::default();
     for (block, data) in body.basic_blocks.iter_enumerated() {
         for (statement_index, stmt) in data.statements.iter().enumerate() {

diff --git a/tests/ui/drop/lint-tail-expr-drop-order-borrowck.rs b/tests/ui/drop/lint-tail-expr-drop-order-borrowck.rs
@@ -0,0 +1,37 @@
+// Edition 2024 lint for change in drop order at tail expression
+// This lint is to capture potential borrow-checking errors
+// due to implementation of RFC 3606 <https://github.com/rust-lang/rfcs/pull/3606>
+//@ edition: 2021
+
+#![deny(tail_expr_drop_order)] //~ NOTE: the lint level is defined here
+
+fn should_lint_with_potential_borrowck_err() {
+    let _ = { String::new().as_str() }.len();
+    //~^ ERROR: a temporary value will be dropped here
+    //~| WARN: this changes meaning in Rust 2024
+    //~| NOTE: consider using a `let` binding
+    //~| NOTE: for more information, see
+}
+
+fn should_lint_with_unsafe_block() {
+    fn f(_: usize) {}
+    f(unsafe { String::new().as_str() }.len());
+    //~^ ERROR: a temporary value will be dropped here
+    //~| WARN: this changes meaning in Rust 2024
+    //~| NOTE: consider using a `let` binding
+    //~| NOTE: for more information, see
+}
+
+#[rustfmt::skip]
+fn should_lint_with_big_block() {
+    fn f<T>(_: T) {}
+    f({
+        &mut || 0
+        //~^ ERROR: a temporary value will be dropped here
+        //~| WARN: this changes meaning in Rust 2024
+        //~| NOTE: consider using a `let` binding
+        //~| NOTE: for more information, see
+    })
+}
+
+fn main() {}
diff --git a/tests/ui/drop/lint-tail-expr-drop-order-borrowck.stderr b/tests/ui/drop/lint-tail-expr-drop-order-borrowck.stderr
@@ -0,0 +1,40 @@
+error: a temporary value will be dropped here before the execution exits the block in Edition 2024, which will raise borrow checking error
+  --> $DIR/lint-tail-expr-drop-order-borrowck.rs:9:36
+   |
+LL |     let _ = { String::new().as_str() }.len();
+   |               -------------        ^
+   |               |
+   |               consider using a `let` binding to create a longer lived value; or replacing the `{ .. }` block with curly brackets `( .. )`; or folding the rest of the expression into the surrounding `unsafe { .. }`
+   |
+   = warning: this changes meaning in Rust 2024
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/temporary-tail-expr-scope.html>
+note: the lint level is defined here
+  --> $DIR/lint-tail-expr-drop-order-borrowck.rs:6:9
+   |
+LL | #![deny(tail_expr_drop_order)]
+   |         ^^^^^^^^^^^^^^^^^^^^
+
+error: a temporary value will be dropped here before the execution exits the block in Edition 2024, which will raise borrow checking error
+  --> $DIR/lint-tail-expr-drop-order-borrowck.rs:18:37
+   |
+LL |     f(unsafe { String::new().as_str() }.len());
+   |                -------------        ^
+   |                |
+   |                consider using a `let` binding to create a longer lived value; or replacing the `{ .. }` block with curly brackets `( .. )`; or folding the rest of the expression into the surrounding `unsafe { .. }`
+   |
+   = warning: this changes meaning in Rust 2024
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/temporary-tail-expr-scope.html>
+
+error: a temporary value will be dropped here before the execution exits the block in Edition 2024, which will raise borrow checking error
+  --> $DIR/lint-tail-expr-drop-order-borrowck.rs:29:17
+   |
+LL |         &mut || 0
+   |         --------^
+   |         |
+   |         consider using a `let` binding to create a longer lived value; or replacing the `{ .. }` block with curly brackets `( .. )`; or folding the rest of the expression into the surrounding `unsafe { .. }`
+   |
+   = warning: this changes meaning in Rust 2024
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/temporary-tail-expr-scope.html>
+
+error: aborting due to 3 previous errors
+
diff --git a/tests/ui/drop/lint-tail-expr-drop-order.rs b/tests/ui/drop/lint-tail-expr-drop-order.rs
@@ -17,7 +17,6 @@ impl Drop for LoudDropper {
     //~| NOTE: `#1` invokes this custom destructor
     //~| NOTE: `x` invokes this custom destructor
     //~| NOTE: `#1` invokes this custom destructor
-    //~| NOTE: `future` invokes this custom destructor
     //~| NOTE: `_x` invokes this custom destructor
     //~| NOTE: `#1` invokes this custom destructor
     fn drop(&mut self) {

diff --git a/tests/ui/drop/lint-tail-expr-drop-order.stderr b/tests/ui/drop/lint-tail-expr-drop-order.stderr
@@ -1,5 +1,5 @@
 error: relative drop order changing in Rust 2024
-  --> $DIR/lint-tail-expr-drop-order.rs:41:15
+  --> $DIR/lint-tail-expr-drop-order.rs:40:15
    |
 LL |     let x = LoudDropper;
    |         -
@@ -40,7 +40,7 @@ LL | #![deny(tail_expr_drop_order)]
    |         ^^^^^^^^^^^^^^^^^^^^
 
 error: relative drop order changing in Rust 2024
-  --> $DIR/lint-tail-expr-drop-order.rs:66:19
+  --> $DIR/lint-tail-expr-drop-order.rs:65:19
    |
 LL |         let x = LoudDropper;
    |             -
@@ -76,7 +76,7 @@ LL | | }
    = note: most of the time, changing drop order is harmless; inspect the `impl Drop`s for side effects like releasing locks or sending messages
 
 error: relative drop order changing in Rust 2024
-  --> $DIR/lint-tail-expr-drop-order.rs:93:7
+  --> $DIR/lint-tail-expr-drop-order.rs:92:7
    |
 LL |     let x = LoudDropper;
    |         -
@@ -112,7 +112,7 @@ LL | | }
    = note: most of the time, changing drop order is harmless; inspect the `impl Drop`s for side effects like releasing locks or sending messages
 
 error: relative drop order changing in Rust 2024
-  --> $DIR/lint-tail-expr-drop-order.rs:146:5
+  --> $DIR/lint-tail-expr-drop-order.rs:145:5
    |
 LL |     let future = f();
    |         ------
@@ -136,19 +136,12 @@ note: `#1` invokes this custom destructor
    |
 LL | / impl Drop for LoudDropper {
 ...  |
-LL | | }
-   | |_^
-note: `future` invokes this custom destructor
-  --> $DIR/lint-tail-expr-drop-order.rs:10:1
-   |
-LL | / impl Drop for LoudDropper {
-...  |
 LL | | }
    | |_^
    = note: most of the time, changing drop order is harmless; inspect the `impl Drop`s for side effects like releasing locks or sending messages
 
 error: relative drop order changing in Rust 2024
-  --> $DIR/lint-tail-expr-drop-order.rs:163:14
+  --> $DIR/lint-tail-expr-drop-order.rs:162:14
    |
 LL |     let x = T::default();
    |         -
@@ -170,7 +163,7 @@ LL | }
    = note: most of the time, changing drop order is harmless; inspect the `impl Drop`s for side effects like releasing locks or sending messages
 
 error: relative drop order changing in Rust 2024
-  --> $DIR/lint-tail-expr-drop-order.rs:177:5
+  --> $DIR/lint-tail-expr-drop-order.rs:176:5
    |
 LL |     let x: Result<LoudDropper, ()> = Ok(LoudDropper);
    |         -
@@ -206,7 +199,7 @@ LL | | }
    = note: most of the time, changing drop order is harmless; inspect the `impl Drop`s for side effects like releasing locks or sending messages
 
 error: relative drop order changing in Rust 2024
-  --> $DIR/lint-tail-expr-drop-order.rs:221:5
+  --> $DIR/lint-tail-expr-drop-order.rs:220:5
    |
 LL |     let x = LoudDropper2;
    |         -
@@ -226,7 +219,7 @@ LL | }
    = warning: this changes meaning in Rust 2024
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/temporary-tail-expr-scope.html>
 note: `#1` invokes this custom destructor
-  --> $DIR/lint-tail-expr-drop-order.rs:194:5
+  --> $DIR/lint-tail-expr-drop-order.rs:193:5
    |
 LL | /     impl Drop for LoudDropper3 {
 LL | |
@@ -236,7 +229,7 @@ LL | |         }
 LL | |     }
    | |_____^
 note: `x` invokes this custom destructor
-  --> $DIR/lint-tail-expr-drop-order.rs:206:5
+  --> $DIR/lint-tail-expr-drop-order.rs:205:5
    |
 LL | /     impl Drop for LoudDropper2 {
 LL | |
@@ -248,7 +241,7 @@ LL | |     }
    = note: most of the time, changing drop order is harmless; inspect the `impl Drop`s for side effects like releasing locks or sending messages
 
 error: relative drop order changing in Rust 2024
-  --> $DIR/lint-tail-expr-drop-order.rs:234:13
+  --> $DIR/lint-tail-expr-drop-order.rs:233:13
    |
 LL |             LoudDropper.get()
    |             ^^^^^^^^^^^