Auto merge of #107844 - Zeegomo:no-drop-and-rep, r=cjgillot

Desugaring of drop and replace at MIR build

This commit desugars the drop and replace deriving from an
assignment at MIR build, avoiding the construction of the
`DropAndReplace` terminator (which will be removed in a following PR).

In order to retain the same error messages for replaces a new
`DesugaringKind::Replace` variant is introduced.

The changes in the borrowck are also useful for future work in moving drop elaboration
before borrowck, as no `DropAndReplace` would be present there anymore.

Notes on test diffs:
*  `tests/ui/borrowck/issue-58776-borrowck-scans-children`: the assignment deriving from the desugaring kills the borrow.
*  `tests/ui/async-await/async-fn-size-uninit-locals.rs`, `tests/mir-opt/issue_41110.test.ElaborateDrops.after.mir`,  `tests/mir-opt/issue_41888.main.ElaborateDrops.after.mir`:  drop elaboration generates (or reads from) a useless drop flag due to an issue with the dataflow analysis. Will be fixed independently by https://github.com/rust-lang/rust/pull/106430.

See https://github.com/rust-lang/rust/pull/104488 for more context

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -1467,6 +1467,32 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 
     /// Reports StorageDeadOrDrop of `place` conflicts with `borrow`.
     ///
+    /// Depending on the origin of the StorageDeadOrDrop, this may be
+    /// reported as either a drop or an illegal mutation of a borrowed value.
+    /// The latter is preferred when the this is a drop triggered by a
+    /// reassignment, as it's more user friendly to report a problem with the
+    /// explicit assignment than the implicit drop.
+    #[instrument(level = "debug", skip(self))]
+    pub(crate) fn report_storage_dead_or_drop_of_borrowed(
+        &mut self,
+        location: Location,
+        place_span: (Place<'tcx>, Span),
+        borrow: &BorrowData<'tcx>,
+    ) {
+        // It's sufficient to check the last desugaring as Replace is the last
+        // one to be applied.
+        if let Some(DesugaringKind::Replace) = place_span.1.desugaring_kind() {
+            self.report_illegal_mutation_of_borrowed(location, place_span, borrow)
+        } else {
+            self.report_borrowed_value_does_not_live_long_enough(
+                location,
+                borrow,
+                place_span,
+                Some(WriteKind::StorageDeadOrDrop),
+            )
+        }
+    }
+
     /// This means that some data referenced by `borrow` needs to live
     /// past the point where the StorageDeadOrDrop of `place` occurs.
     /// This is usually interpreted as meaning that `place` has too

compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -925,7 +925,20 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             return OtherUse(use_span);
         }
 
-        for stmt in &self.body[location.block].statements[location.statement_index + 1..] {
+        // drop and replace might have moved the assignment to the next block
+        let maybe_additional_statement =
+            if let TerminatorKind::Drop { target: drop_target, .. } =
+                self.body[location.block].terminator().kind
+            {
+                self.body[drop_target].statements.first()
+            } else {
+                None
+            };
+
+        let statements =
+            self.body[location.block].statements[location.statement_index + 1..].iter();
+
+        for stmt in statements.chain(maybe_additional_statement) {
             if let StatementKind::Assign(box (_, Rvalue::Aggregate(kind, places))) = &stmt.kind {
                 let (&def_id, is_generator) = match kind {
                     box AggregateKind::Closure(def_id, _) => (def_id, false),

compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

@@ -828,7 +828,13 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
             let Some(hir::Node::Item(item)) = node else { return; };
             let hir::ItemKind::Fn(.., body_id) = item.kind else { return; };
             let body = self.infcx.tcx.hir().body(body_id);
-            let mut v = V { assign_span: span, err, ty, suggested: false };
+            let mut assign_span = span;
+            // Drop desugaring is done at MIR build so it's not in the HIR
+            if let Some(DesugaringKind::Replace) = span.desugaring_kind() {
+                assign_span.remove_mark();
+            }
+
+            let mut v = V { assign_span, err, ty, suggested: false };
             v.visit_body(body);
             if !v.suggested {
                 err.help(&format!(

compiler/rustc_borrowck/src/lib.rs

@@ -1185,12 +1185,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                             this.buffer_error(err);
                         }
                         WriteKind::StorageDeadOrDrop => this
-                            .report_borrowed_value_does_not_live_long_enough(
+                            .report_storage_dead_or_drop_of_borrowed(location, place_span, borrow),
-                                location,
-                                borrow,
-                                place_span,
-                                Some(kind),
-                            ),
                         WriteKind::Mutate => {
                             this.report_illegal_mutation_of_borrowed(location, place_span, borrow)
                         }

compiler/rustc_mir_build/src/build/expr/stmt.rs

@@ -40,7 +40,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 // Generate better code for things that don't need to be
                 // dropped.
                 if lhs.ty.needs_drop(this.tcx, this.param_env) {
-                    let rhs = unpack!(block = this.as_local_operand(block, rhs));
+                    let rhs = unpack!(block = this.as_local_rvalue(block, rhs));
                     let lhs = unpack!(block = this.as_place(block, lhs));
                     unpack!(block = this.build_drop_and_replace(block, lhs_span, lhs, rhs));
                 } else {

compiler/rustc_mir_build/src/build/scope.rs

@@ -91,7 +91,7 @@ use rustc_middle::middle::region;
 use rustc_middle::mir::*;
 use rustc_middle::thir::{Expr, LintLevel};
 
-use rustc_span::{Span, DUMMY_SP};
+use rustc_span::{DesugaringKind, Span, DUMMY_SP};
 
 #[derive(Debug)]
 pub struct Scopes<'tcx> {
@@ -1118,24 +1118,35 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     }
 
     /// Utility function for *non*-scope code to build their own drops
+    /// Force a drop at this point in the MIR by creating a new block.
     pub(crate) fn build_drop_and_replace(
         &mut self,
         block: BasicBlock,
         span: Span,
         place: Place<'tcx>,
-        value: Operand<'tcx>,
+        value: Rvalue<'tcx>,
     ) -> BlockAnd<()> {
+        let span = self.tcx.with_stable_hashing_context(|hcx| {
+            span.mark_with_reason(None, DesugaringKind::Replace, self.tcx.sess.edition(), hcx)
+        });
         let source_info = self.source_info(span);
-        let next_target = self.cfg.start_new_block();
+
+        // create the new block for the assignment
+        let assign = self.cfg.start_new_block();
+        self.cfg.push_assign(assign, source_info, place, value.clone());
+
+        // create the new block for the assignment in the case of unwinding
+        let assign_unwind = self.cfg.start_new_cleanup_block();
+        self.cfg.push_assign(assign_unwind, source_info, place, value.clone());
 
         self.cfg.terminate(
             block,
             source_info,
-            TerminatorKind::DropAndReplace { place, value, target: next_target, unwind: None },
+            TerminatorKind::Drop { place, target: assign, unwind: Some(assign_unwind) },
         );
         self.diverge_from(block);
 
-        next_target.unit()
+        assign.unit()
     }
 
     /// Creates an `Assert` terminator and return the success block.
@@ -1413,8 +1424,15 @@ impl<'tcx> DropTreeBuilder<'tcx> for Unwind {
     fn add_entry(cfg: &mut CFG<'tcx>, from: BasicBlock, to: BasicBlock) {
         let term = &mut cfg.block_data_mut(from).terminator_mut();
         match &mut term.kind {
-            TerminatorKind::Drop { unwind, .. }
+            TerminatorKind::Drop { unwind, .. } => {
-            | TerminatorKind::DropAndReplace { unwind, .. }
+                if let Some(unwind) = *unwind {
+                    let source_info = term.source_info;
+                    cfg.terminate(unwind, source_info, TerminatorKind::Goto { target: to });
+                } else {
+                    *unwind = Some(to);
+                }
+            }
+            TerminatorKind::DropAndReplace { unwind, .. }
             | TerminatorKind::FalseUnwind { unwind, .. }
             | TerminatorKind::Call { cleanup: unwind, .. }
             | TerminatorKind::Assert { cleanup: unwind, .. }

compiler/rustc_mir_transform/src/elaborate_drops.rs

@@ -14,7 +14,7 @@ use rustc_mir_dataflow::un_derefer::UnDerefer;
 use rustc_mir_dataflow::MoveDataParamEnv;
 use rustc_mir_dataflow::{on_all_children_bits, on_all_drop_children_bits};
 use rustc_mir_dataflow::{Analysis, ResultsCursor};
-use rustc_span::Span;
+use rustc_span::{DesugaringKind, Span};
 use rustc_target::abi::VariantIdx;
 use std::fmt;
 
@@ -425,11 +425,20 @@ impl<'b, 'tcx> ElaborateDropsCtxt<'b, 'tcx> {
                             bb,
                         ),
                         LookupResult::Parent(..) => {
+                            if !matches!(
+                                terminator.source_info.span.desugaring_kind(),
+                                Some(DesugaringKind::Replace),
+                            ) {
                                 self.tcx.sess.delay_span_bug(
                                     terminator.source_info.span,
                                     &format!("drop of untracked value {:?}", bb),
                                 );
                             }
+                            // A drop and replace behind a pointer/array/whatever.
+                            // The borrow checker requires that these locations are initialized before the assignment,
+                            // so we just leave an unconditional drop.
+                            assert!(!data.is_cleanup);
+                        }
                     }
                 }
                 TerminatorKind::DropAndReplace { mut place, ref value, target, unwind } => {

compiler/rustc_span/src/hygiene.rs

@@ -1151,6 +1151,7 @@ pub enum DesugaringKind {
     Await,
     ForLoop,
     WhileLoop,
+    Replace,
 }
 
 impl DesugaringKind {
@@ -1166,6 +1167,7 @@ impl DesugaringKind {
             DesugaringKind::OpaqueTy => "`impl Trait`",
             DesugaringKind::ForLoop => "`for` loop",
             DesugaringKind::WhileLoop => "`while` loop",
+            DesugaringKind::Replace => "drop and replace",
         }
     }
 }

tests/mir-opt/basic_assignment.main.ElaborateDrops.diff

@@ -0,0 +1,85 @@
+- // MIR for `main` before ElaborateDrops
++ // MIR for `main` after ElaborateDrops
+  
+  fn main() -> () {
+      let mut _0: ();                      // return place in scope 0 at $DIR/basic_assignment.rs:+0:11: +0:11
+      let _1: bool;                        // in scope 0 at $DIR/basic_assignment.rs:+1:9: +1:17
+      let mut _3: bool;                    // in scope 0 at $DIR/basic_assignment.rs:+6:16: +6:24
+      let mut _6: std::option::Option<std::boxed::Box<u32>>; // in scope 0 at $DIR/basic_assignment.rs:+13:14: +13:20
+      scope 1 {
+          debug nodrop_x => _1;            // in scope 1 at $DIR/basic_assignment.rs:+1:9: +1:17
+          let _2: bool;                    // in scope 1 at $DIR/basic_assignment.rs:+2:9: +2:17
+          scope 2 {
+              debug nodrop_y => _2;        // in scope 2 at $DIR/basic_assignment.rs:+2:9: +2:17
+              let _4: std::option::Option<std::boxed::Box<u32>>; // in scope 2 at $DIR/basic_assignment.rs:+8:9: +8:15
+              scope 3 {
+                  debug drop_x => _4;      // in scope 3 at $DIR/basic_assignment.rs:+8:9: +8:15
+                  let _5: std::option::Option<std::boxed::Box<u32>>; // in scope 3 at $DIR/basic_assignment.rs:+9:9: +9:15
+                  scope 4 {
+                      debug drop_y => _5;  // in scope 4 at $DIR/basic_assignment.rs:+9:9: +9:15
+                  }
+              }
+          }
+      }
+  
+      bb0: {
+          StorageLive(_1);                 // scope 0 at $DIR/basic_assignment.rs:+1:9: +1:17
+          _1 = const false;                // scope 0 at $DIR/basic_assignment.rs:+1:20: +1:25
+          StorageLive(_2);                 // scope 1 at $DIR/basic_assignment.rs:+2:9: +2:17
+          StorageLive(_3);                 // scope 2 at $DIR/basic_assignment.rs:+6:16: +6:24
+          _3 = _1;                         // scope 2 at $DIR/basic_assignment.rs:+6:16: +6:24
+          _2 = move _3;                    // scope 2 at $DIR/basic_assignment.rs:+6:5: +6:24
+          StorageDead(_3);                 // scope 2 at $DIR/basic_assignment.rs:+6:23: +6:24
+          StorageLive(_4);                 // scope 2 at $DIR/basic_assignment.rs:+8:9: +8:15
+          _4 = Option::<Box<u32>>::None;   // scope 2 at $DIR/basic_assignment.rs:+8:36: +8:40
+          StorageLive(_5);                 // scope 3 at $DIR/basic_assignment.rs:+9:9: +9:15
+          StorageLive(_6);                 // scope 4 at $DIR/basic_assignment.rs:+13:14: +13:20
+          _6 = move _4;                    // scope 4 at $DIR/basic_assignment.rs:+13:14: +13:20
+-         drop(_5) -> [return: bb1, unwind: bb2]; // scope 4 at $DIR/basic_assignment.rs:+13:5: +13:11
++         goto -> bb1;                     // scope 4 at $DIR/basic_assignment.rs:+13:5: +13:11
+      }
+  
+      bb1: {
+          _5 = move _6;                    // scope 4 at $DIR/basic_assignment.rs:+13:5: +13:11
+-         drop(_6) -> [return: bb3, unwind: bb6]; // scope 4 at $DIR/basic_assignment.rs:+13:19: +13:20
++         goto -> bb3;                     // scope 4 at $DIR/basic_assignment.rs:+13:19: +13:20
+      }
+  
+      bb2 (cleanup): {
+          _5 = move _6;                    // scope 4 at $DIR/basic_assignment.rs:+13:5: +13:11
+          drop(_6) -> bb6;                 // scope 4 at $DIR/basic_assignment.rs:+13:19: +13:20
+      }
+  
+      bb3: {
+          StorageDead(_6);                 // scope 4 at $DIR/basic_assignment.rs:+13:19: +13:20
+          _0 = const ();                   // scope 0 at $DIR/basic_assignment.rs:+0:11: +14:2
+          drop(_5) -> [return: bb4, unwind: bb7]; // scope 3 at $DIR/basic_assignment.rs:+14:1: +14:2
+      }
+  
+      bb4: {
+          StorageDead(_5);                 // scope 3 at $DIR/basic_assignment.rs:+14:1: +14:2
+-         drop(_4) -> bb5;                 // scope 2 at $DIR/basic_assignment.rs:+14:1: +14:2
++         goto -> bb5;                     // scope 2 at $DIR/basic_assignment.rs:+14:1: +14:2
+      }
+  
+      bb5: {
+          StorageDead(_4);                 // scope 2 at $DIR/basic_assignment.rs:+14:1: +14:2
+          StorageDead(_2);                 // scope 1 at $DIR/basic_assignment.rs:+14:1: +14:2
+          StorageDead(_1);                 // scope 0 at $DIR/basic_assignment.rs:+14:1: +14:2
+          return;                          // scope 0 at $DIR/basic_assignment.rs:+14:2: +14:2
+      }
+  
+      bb6 (cleanup): {
+          drop(_5) -> bb7;                 // scope 3 at $DIR/basic_assignment.rs:+14:1: +14:2
+      }
+  
+      bb7 (cleanup): {
+-         drop(_4) -> bb8;                 // scope 2 at $DIR/basic_assignment.rs:+14:1: +14:2
++         goto -> bb8;                     // scope 2 at $DIR/basic_assignment.rs:+14:1: +14:2
+      }
+  
+      bb8 (cleanup): {
+          resume;                          // scope 0 at $DIR/basic_assignment.rs:+0:1: +14:2
+      }
+  }
+  

tests/mir-opt/basic_assignment.main.SimplifyCfg-initial.after.mir

@@ -1,8 +1,8 @@
 // MIR for `main` after SimplifyCfg-initial
 
 | User Type Annotations
-| 0: user_ty: Canonical { max_universe: U0, variables: [], value: Ty(std::option::Option<std::boxed::Box<u32>>) }, span: $DIR/basic_assignment.rs:18:17: 18:33, inferred_ty: std::option::Option<std::boxed::Box<u32>>
+| 0: user_ty: Canonical { max_universe: U0, variables: [], value: Ty(std::option::Option<std::boxed::Box<u32>>) }, span: $DIR/basic_assignment.rs:20:17: 20:33, inferred_ty: std::option::Option<std::boxed::Box<u32>>
-| 1: user_ty: Canonical { max_universe: U0, variables: [], value: Ty(std::option::Option<std::boxed::Box<u32>>) }, span: $DIR/basic_assignment.rs:18:17: 18:33, inferred_ty: std::option::Option<std::boxed::Box<u32>>
+| 1: user_ty: Canonical { max_universe: U0, variables: [], value: Ty(std::option::Option<std::boxed::Box<u32>>) }, span: $DIR/basic_assignment.rs:20:17: 20:33, inferred_ty: std::option::Option<std::boxed::Box<u32>>
 |
 fn main() -> () {
     let mut _0: ();                      // return place in scope 0 at $DIR/basic_assignment.rs:+0:11: +0:11
@@ -41,35 +41,37 @@ fn main() -> () {
         StorageLive(_5);                 // scope 3 at $DIR/basic_assignment.rs:+9:9: +9:15
         StorageLive(_6);                 // scope 4 at $DIR/basic_assignment.rs:+13:14: +13:20
         _6 = move _4;                    // scope 4 at $DIR/basic_assignment.rs:+13:14: +13:20
-        replace(_5 <- move _6) -> [return: bb1, unwind: bb5]; // scope 4 at $DIR/basic_assignment.rs:+13:5: +13:11
+        drop(_5) -> [return: bb1, unwind: bb2]; // scope 4 at $DIR/basic_assignment.rs:+13:5: +13:11
     }
 
     bb1: {
-        drop(_6) -> [return: bb2, unwind: bb6]; // scope 4 at $DIR/basic_assignment.rs:+13:19: +13:20
+        _5 = move _6;                    // scope 4 at $DIR/basic_assignment.rs:+13:5: +13:11
+        drop(_6) -> [return: bb3, unwind: bb6]; // scope 4 at $DIR/basic_assignment.rs:+13:19: +13:20
     }
 
-    bb2: {
+    bb2 (cleanup): {
-        StorageDead(_6);                 // scope 4 at $DIR/basic_assignment.rs:+13:19: +13:20
+        _5 = move _6;                    // scope 4 at $DIR/basic_assignment.rs:+13:5: +13:11
-        _0 = const ();                   // scope 0 at $DIR/basic_assignment.rs:+0:11: +14:2
+        drop(_6) -> bb6;                 // scope 4 at $DIR/basic_assignment.rs:+13:19: +13:20
-        drop(_5) -> [return: bb3, unwind: bb7]; // scope 3 at $DIR/basic_assignment.rs:+14:1: +14:2
     }
 
     bb3: {
-        StorageDead(_5);                 // scope 3 at $DIR/basic_assignment.rs:+14:1: +14:2
+        StorageDead(_6);                 // scope 4 at $DIR/basic_assignment.rs:+13:19: +13:20
-        drop(_4) -> [return: bb4, unwind: bb8]; // scope 2 at $DIR/basic_assignment.rs:+14:1: +14:2
+        _0 = const ();                   // scope 0 at $DIR/basic_assignment.rs:+0:11: +14:2
+        drop(_5) -> [return: bb4, unwind: bb7]; // scope 3 at $DIR/basic_assignment.rs:+14:1: +14:2
     }
 
     bb4: {
+        StorageDead(_5);                 // scope 3 at $DIR/basic_assignment.rs:+14:1: +14:2
+        drop(_4) -> [return: bb5, unwind: bb8]; // scope 2 at $DIR/basic_assignment.rs:+14:1: +14:2
+    }
+
+    bb5: {
         StorageDead(_4);                 // scope 2 at $DIR/basic_assignment.rs:+14:1: +14:2
         StorageDead(_2);                 // scope 1 at $DIR/basic_assignment.rs:+14:1: +14:2
         StorageDead(_1);                 // scope 0 at $DIR/basic_assignment.rs:+14:1: +14:2
         return;                          // scope 0 at $DIR/basic_assignment.rs:+14:2: +14:2
     }
 
-    bb5 (cleanup): {
-        drop(_6) -> bb6;                 // scope 4 at $DIR/basic_assignment.rs:+13:19: +13:20
-    }
-
     bb6 (cleanup): {
         drop(_5) -> bb7;                 // scope 3 at $DIR/basic_assignment.rs:+14:1: +14:2
     }

tests/mir-opt/basic_assignment.rs

@@ -1,5 +1,7 @@
+// needs-unwind
 // this tests move up progration, which is not yet implemented
 
+// EMIT_MIR basic_assignment.main.ElaborateDrops.diff
 // EMIT_MIR basic_assignment.main.SimplifyCfg-initial.after.mir
 
 // Check codegen for assignments (`a = b`) where the left-hand-side is

tests/mir-opt/issue_41110.test.ElaborateDrops.diff

@@ -38,37 +38,39 @@
           StorageLive(_5);                 // scope 2 at $DIR/issue_41110.rs:+4:9: +4:10
 +         _6 = const false;                // scope 2 at $DIR/issue_41110.rs:+4:9: +4:10
           _5 = move _1;                    // scope 2 at $DIR/issue_41110.rs:+4:9: +4:10
--         replace(_2 <- move _5) -> [return: bb2, unwind: bb6]; // scope 2 at $DIR/issue_41110.rs:+4:5: +4:6
+-         drop(_2) -> [return: bb2, unwind: bb3]; // scope 2 at $DIR/issue_41110.rs:+4:5: +4:6
-+         goto -> bb12;                    // scope 2 at $DIR/issue_41110.rs:+4:5: +4:6
++         goto -> bb2;                     // scope 2 at $DIR/issue_41110.rs:+4:5: +4:6
       }
   
       bb2: {
--         drop(_5) -> [return: bb3, unwind: bb8]; // scope 2 at $DIR/issue_41110.rs:+4:9: +4:10
+          _2 = move _5;                    // scope 2 at $DIR/issue_41110.rs:+4:5: +4:6
-+         goto -> bb3;                     // scope 2 at $DIR/issue_41110.rs:+4:9: +4:10
+-         drop(_5) -> [return: bb4, unwind: bb8]; // scope 2 at $DIR/issue_41110.rs:+4:9: +4:10
++         goto -> bb4;                     // scope 2 at $DIR/issue_41110.rs:+4:9: +4:10
       }
   
-      bb3: {
+      bb3 (cleanup): {
-          StorageDead(_5);                 // scope 2 at $DIR/issue_41110.rs:+4:9: +4:10
+          _2 = move _5;                    // scope 2 at $DIR/issue_41110.rs:+4:5: +4:6
-          _0 = const ();                   // scope 0 at $DIR/issue_41110.rs:+0:15: +5:2
+          drop(_5) -> bb8;                 // scope 2 at $DIR/issue_41110.rs:+4:9: +4:10
-          drop(_2) -> [return: bb4, unwind: bb9]; // scope 1 at $DIR/issue_41110.rs:+5:1: +5:2
       }
   
       bb4: {
-          StorageDead(_2);                 // scope 1 at $DIR/issue_41110.rs:+5:1: +5:2
+          StorageDead(_5);                 // scope 2 at $DIR/issue_41110.rs:+4:9: +4:10
--         drop(_1) -> bb5;                 // scope 0 at $DIR/issue_41110.rs:+5:1: +5:2
+          _0 = const ();                   // scope 0 at $DIR/issue_41110.rs:+0:15: +5:2
-+         goto -> bb5;                     // scope 0 at $DIR/issue_41110.rs:+5:1: +5:2
+          drop(_2) -> [return: bb5, unwind: bb9]; // scope 1 at $DIR/issue_41110.rs:+5:1: +5:2
       }
   
       bb5: {
+          StorageDead(_2);                 // scope 1 at $DIR/issue_41110.rs:+5:1: +5:2
+-         drop(_1) -> bb6;                 // scope 0 at $DIR/issue_41110.rs:+5:1: +5:2
++         goto -> bb6;                     // scope 0 at $DIR/issue_41110.rs:+5:1: +5:2
+      }
+  
+      bb6: {
 +         _6 = const false;                // scope 0 at $DIR/issue_41110.rs:+5:1: +5:2
           StorageDead(_1);                 // scope 0 at $DIR/issue_41110.rs:+5:1: +5:2
           return;                          // scope 0 at $DIR/issue_41110.rs:+5:2: +5:2
       }
   
-      bb6 (cleanup): {
-          drop(_5) -> bb8;                 // scope 2 at $DIR/issue_41110.rs:+4:9: +4:10
-      }
-  
       bb7 (cleanup): {
 -         drop(_4) -> bb8;                 // scope 2 at $DIR/issue_41110.rs:+3:11: +3:12
 +         goto -> bb8;                     // scope 2 at $DIR/issue_41110.rs:+3:11: +3:12
@@ -81,7 +83,7 @@
   
       bb9 (cleanup): {
 -         drop(_1) -> bb10;                // scope 0 at $DIR/issue_41110.rs:+5:1: +5:2
-+         goto -> bb14;                    // scope 0 at $DIR/issue_41110.rs:+5:1: +5:2
++         goto -> bb12;                    // scope 0 at $DIR/issue_41110.rs:+5:1: +5:2
       }
   
       bb10 (cleanup): {
@@ -89,21 +91,11 @@
 +     }
 + 
 +     bb11 (cleanup): {
-+         _2 = move _5;                    // scope 2 at $DIR/issue_41110.rs:+4:5: +4:6
-+         goto -> bb10;                    // scope 2 at $DIR/issue_41110.rs:+4:5: +4:6
-+     }
-+ 
-+     bb12: {
-+         _2 = move _5;                    // scope 2 at $DIR/issue_41110.rs:+4:5: +4:6
-+         goto -> bb2;                     // scope 2 at $DIR/issue_41110.rs:+4:5: +4:6
-+     }
-+ 
-+     bb13 (cleanup): {
 +         drop(_1) -> bb10;                // scope 0 at $DIR/issue_41110.rs:+5:1: +5:2
 +     }
 + 
-+     bb14 (cleanup): {
++     bb12 (cleanup): {
-+         switchInt(_6) -> [0: bb10, otherwise: bb13]; // scope 0 at $DIR/issue_41110.rs:+5:1: +5:2
++         switchInt(_6) -> [0: bb10, otherwise: bb11]; // scope 0 at $DIR/issue_41110.rs:+5:1: +5:2
       }
   }
   

tests/mir-opt/issue_41888.main.ElaborateDrops.diff

@@ -34,7 +34,7 @@
       }
   
       bb1: {
-          switchInt(move _2) -> [0: bb7, otherwise: bb2]; // scope 1 at $DIR/issue_41888.rs:+2:8: +2:14
+          switchInt(move _2) -> [0: bb8, otherwise: bb2]; // scope 1 at $DIR/issue_41888.rs:+2:8: +2:14
       }
   
       bb2: {
@@ -43,47 +43,56 @@
           _4 = K;                          // scope 1 at $DIR/issue_41888.rs:+3:18: +3:19
           _3 = E::F(move _4);              // scope 1 at $DIR/issue_41888.rs:+3:13: +3:20
           StorageDead(_4);                 // scope 1 at $DIR/issue_41888.rs:+3:19: +3:20
--         replace(_1 <- move _3) -> [return: bb3, unwind: bb10]; // scope 1 at $DIR/issue_41888.rs:+3:9: +3:10
+-         drop(_1) -> [return: bb3, unwind: bb4]; // scope 1 at $DIR/issue_41888.rs:+3:9: +3:10
-+         goto -> bb14;                    // scope 1 at $DIR/issue_41888.rs:+3:9: +3:10
++         goto -> bb3;                     // scope 1 at $DIR/issue_41888.rs:+3:9: +3:10
       }
   
       bb3: {
--         drop(_3) -> [return: bb4, unwind: bb11]; // scope 1 at $DIR/issue_41888.rs:+3:19: +3:20
++         _7 = const true;                 // scope 1 at $DIR/issue_41888.rs:+3:9: +3:10
-+         goto -> bb4;                     // scope 1 at $DIR/issue_41888.rs:+3:19: +3:20
++         _8 = const true;                 // scope 1 at $DIR/issue_41888.rs:+3:9: +3:10
++         _9 = const true;                 // scope 1 at $DIR/issue_41888.rs:+3:9: +3:10
+          _1 = move _3;                    // scope 1 at $DIR/issue_41888.rs:+3:9: +3:10
+-         drop(_3) -> [return: bb5, unwind: bb11]; // scope 1 at $DIR/issue_41888.rs:+3:19: +3:20
++         goto -> bb5;                     // scope 1 at $DIR/issue_41888.rs:+3:19: +3:20
       }
   
-      bb4: {
+      bb4 (cleanup): {
-          StorageDead(_3);                 // scope 1 at $DIR/issue_41888.rs:+3:19: +3:20
+          _1 = move _3;                    // scope 1 at $DIR/issue_41888.rs:+3:9: +3:10
-          _5 = discriminant(_1);           // scope 2 at $DIR/issue_41888.rs:+4:16: +4:24
+          drop(_3) -> bb11;                // scope 1 at $DIR/issue_41888.rs:+3:19: +3:20
-          switchInt(move _5) -> [0: bb5, otherwise: bb6]; // scope 2 at $DIR/issue_41888.rs:+4:16: +4:24
       }
   
       bb5: {
+          StorageDead(_3);                 // scope 1 at $DIR/issue_41888.rs:+3:19: +3:20
+          _5 = discriminant(_1);           // scope 2 at $DIR/issue_41888.rs:+4:16: +4:24
+          switchInt(move _5) -> [0: bb6, otherwise: bb7]; // scope 2 at $DIR/issue_41888.rs:+4:16: +4:24
+      }
+  
+      bb6: {
           StorageLive(_6);                 // scope 2 at $DIR/issue_41888.rs:+4:21: +4:23
 +         _9 = const false;                // scope 2 at $DIR/issue_41888.rs:+4:21: +4:23
           _6 = move ((_1 as F).0: K);      // scope 2 at $DIR/issue_41888.rs:+4:21: +4:23
           _0 = const ();                   // scope 2 at $DIR/issue_41888.rs:+4:29: +7:10
           StorageDead(_6);                 // scope 1 at $DIR/issue_41888.rs:+7:9: +7:10
-          goto -> bb8;                     // scope 1 at $DIR/issue_41888.rs:+4:9: +7:10
+          goto -> bb9;                     // scope 1 at $DIR/issue_41888.rs:+4:9: +7:10
-      }
-  
-      bb6: {
-          _0 = const ();                   // scope 1 at $DIR/issue_41888.rs:+7:10: +7:10
-          goto -> bb8;                     // scope 1 at $DIR/issue_41888.rs:+4:9: +7:10
       }
   
       bb7: {
-          _0 = const ();                   // scope 1 at $DIR/issue_41888.rs:+8:6: +8:6
+          _0 = const ();                   // scope 1 at $DIR/issue_41888.rs:+7:10: +7:10
-          goto -> bb8;                     // scope 1 at $DIR/issue_41888.rs:+2:5: +8:6
+          goto -> bb9;                     // scope 1 at $DIR/issue_41888.rs:+4:9: +7:10
       }
   
       bb8: {
-          StorageDead(_2);                 // scope 1 at $DIR/issue_41888.rs:+8:5: +8:6
+          _0 = const ();                   // scope 1 at $DIR/issue_41888.rs:+8:6: +8:6
--         drop(_1) -> bb9;                 // scope 0 at $DIR/issue_41888.rs:+9:1: +9:2
+          goto -> bb9;                     // scope 1 at $DIR/issue_41888.rs:+2:5: +8:6
-+         goto -> bb20;                    // scope 0 at $DIR/issue_41888.rs:+9:1: +9:2
       }
   
       bb9: {
+          StorageDead(_2);                 // scope 1 at $DIR/issue_41888.rs:+8:5: +8:6
+-         drop(_1) -> bb10;                // scope 0 at $DIR/issue_41888.rs:+9:1: +9:2
++         goto -> bb18;                    // scope 0 at $DIR/issue_41888.rs:+9:1: +9:2
+      }
+  
+      bb10: {
 +         _7 = const false;                // scope 0 at $DIR/issue_41888.rs:+9:1: +9:2
 +         _8 = const false;                // scope 0 at $DIR/issue_41888.rs:+9:1: +9:2
 +         _9 = const false;                // scope 0 at $DIR/issue_41888.rs:+9:1: +9:2
@@ -91,10 +100,6 @@
           return;                          // scope 0 at $DIR/issue_41888.rs:+9:2: +9:2
       }
   
-      bb10 (cleanup): {
-          drop(_3) -> bb11;                // scope 1 at $DIR/issue_41888.rs:+3:19: +3:20
-      }
-  
       bb11 (cleanup): {
 -         drop(_1) -> bb12;                // scope 0 at $DIR/issue_41888.rs:+9:1: +9:2
 +         goto -> bb12;                    // scope 0 at $DIR/issue_41888.rs:+9:1: +9:2
@@ -104,55 +109,39 @@
           resume;                          // scope 0 at $DIR/issue_41888.rs:+0:1: +9:2
 +     }
 + 
-+     bb13 (cleanup): {
++     bb13: {
-+         _7 = const true;                 // scope 1 at $DIR/issue_41888.rs:+3:9: +3:10
-+         _8 = const true;                 // scope 1 at $DIR/issue_41888.rs:+3:9: +3:10
-+         _9 = const true;                 // scope 1 at $DIR/issue_41888.rs:+3:9: +3:10
-+         _1 = move _3;                    // scope 1 at $DIR/issue_41888.rs:+3:9: +3:10
-+         goto -> bb12;                    // scope 1 at $DIR/issue_41888.rs:+3:9: +3:10
-+     }
-+ 
-+     bb14: {
-+         _7 = const true;                 // scope 1 at $DIR/issue_41888.rs:+3:9: +3:10
-+         _8 = const true;                 // scope 1 at $DIR/issue_41888.rs:+3:9: +3:10
-+         _9 = const true;                 // scope 1 at $DIR/issue_41888.rs:+3:9: +3:10
-+         _1 = move _3;                    // scope 1 at $DIR/issue_41888.rs:+3:9: +3:10
-+         goto -> bb3;                     // scope 1 at $DIR/issue_41888.rs:+3:9: +3:10
-+     }
-+ 
-+     bb15: {
 +         _7 = const false;                // scope 0 at $DIR/issue_41888.rs:+9:1: +9:2
-+         goto -> bb9;                     // scope 0 at $DIR/issue_41888.rs:+9:1: +9:2
++         goto -> bb10;                    // scope 0 at $DIR/issue_41888.rs:+9:1: +9:2
 +     }
 + 
-+     bb16 (cleanup): {
++     bb14 (cleanup): {
 +         goto -> bb12;                    // scope 0 at $DIR/issue_41888.rs:+9:1: +9:2
 +     }
 + 
-+     bb17: {
++     bb15: {
-+         drop(_1) -> [return: bb15, unwind: bb12]; // scope 0 at $DIR/issue_41888.rs:+9:1: +9:2
++         drop(_1) -> [return: bb13, unwind: bb12]; // scope 0 at $DIR/issue_41888.rs:+9:1: +9:2
 +     }
 + 
-+     bb18 (cleanup): {
++     bb16 (cleanup): {
 +         drop(_1) -> bb12;                // scope 0 at $DIR/issue_41888.rs:+9:1: +9:2
 +     }
 + 
-+     bb19: {
++     bb17: {
 +         _10 = discriminant(_1);          // scope 0 at $DIR/issue_41888.rs:+9:1: +9:2
-+         switchInt(move _10) -> [0: bb15, otherwise: bb17]; // scope 0 at $DIR/issue_41888.rs:+9:1: +9:2
++         switchInt(move _10) -> [0: bb13, otherwise: bb15]; // scope 0 at $DIR/issue_41888.rs:+9:1: +9:2
 +     }
 + 
-+     bb20: {
++     bb18: {
-+         switchInt(_7) -> [0: bb15, otherwise: bb19]; // scope 0 at $DIR/issue_41888.rs:+9:1: +9:2
++         switchInt(_7) -> [0: bb13, otherwise: bb17]; // scope 0 at $DIR/issue_41888.rs:+9:1: +9:2
 +     }
 + 
-+     bb21 (cleanup): {
++     bb19 (cleanup): {
 +         _11 = discriminant(_1);          // scope 0 at $DIR/issue_41888.rs:+9:1: +9:2
-+         switchInt(move _11) -> [0: bb16, otherwise: bb18]; // scope 0 at $DIR/issue_41888.rs:+9:1: +9:2
++         switchInt(move _11) -> [0: bb14, otherwise: bb16]; // scope 0 at $DIR/issue_41888.rs:+9:1: +9:2
 +     }
 + 
-+     bb22 (cleanup): {
++     bb20 (cleanup): {
-+         switchInt(_7) -> [0: bb12, otherwise: bb21]; // scope 0 at $DIR/issue_41888.rs:+9:1: +9:2
++         switchInt(_7) -> [0: bb12, otherwise: bb19]; // scope 0 at $DIR/issue_41888.rs:+9:1: +9:2
       }
   }
   

tests/mir-opt/packed_struct_drop_aligned.main.SimplifyCfg-elaborate-drops.after.mir

@@ -28,21 +28,21 @@ fn main() -> () {
         StorageDead(_5);                 // scope 1 at $DIR/packed_struct_drop_aligned.rs:+2:28: +2:29
         StorageLive(_6);                 // scope 1 at $DIR/packed_struct_drop_aligned.rs:+2:5: +2:8
         _6 = move (_1.0: Aligned);       // scope 1 at $DIR/packed_struct_drop_aligned.rs:+2:5: +2:8
-        drop(_6) -> [return: bb4, unwind: bb3]; // scope 1 at $DIR/packed_struct_drop_aligned.rs:+2:5: +2:8
+        drop(_6) -> [return: bb4, unwind: bb1]; // scope 1 at $DIR/packed_struct_drop_aligned.rs:+2:5: +2:8
     }
 
-    bb1: {
+    bb1 (cleanup): {
+        (_1.0: Aligned) = move _4;       // scope 1 at $DIR/packed_struct_drop_aligned.rs:+2:5: +2:8
+        drop(_1) -> bb3;                 // scope 0 at $DIR/packed_struct_drop_aligned.rs:+3:1: +3:2
+    }
+
+    bb2: {
         StorageDead(_1);                 // scope 0 at $DIR/packed_struct_drop_aligned.rs:+3:1: +3:2
         return;                          // scope 0 at $DIR/packed_struct_drop_aligned.rs:+3:2: +3:2
     }
 
-    bb2 (cleanup): {
-        resume;                          // scope 0 at $DIR/packed_struct_drop_aligned.rs:+0:1: +3:2
-    }
-
     bb3 (cleanup): {
-        (_1.0: Aligned) = move _4;       // scope 1 at $DIR/packed_struct_drop_aligned.rs:+2:5: +2:8
+        resume;                          // scope 0 at $DIR/packed_struct_drop_aligned.rs:+0:1: +3:2
-        drop(_1) -> bb2;                 // scope 0 at $DIR/packed_struct_drop_aligned.rs:+3:1: +3:2
     }
 
     bb4: {
@@ -50,6 +50,6 @@ fn main() -> () {
         (_1.0: Aligned) = move _4;       // scope 1 at $DIR/packed_struct_drop_aligned.rs:+2:5: +2:8
         StorageDead(_4);                 // scope 1 at $DIR/packed_struct_drop_aligned.rs:+2:28: +2:29
         _0 = const ();                   // scope 0 at $DIR/packed_struct_drop_aligned.rs:+0:11: +3:2
-        drop(_1) -> [return: bb1, unwind: bb2]; // scope 0 at $DIR/packed_struct_drop_aligned.rs:+3:1: +3:2
+        drop(_1) -> [return: bb2, unwind: bb3]; // scope 0 at $DIR/packed_struct_drop_aligned.rs:+3:1: +3:2
     }
 }

tests/run-make/coverage-reports/expected_show_coverage.closure.txt

@@ -29,8 +29,8 @@
    29|      1|    some_string = Some(String::from("the string content"));
    30|      1|    let
    31|      1|        a
-   32|      1|    =
+   32|       |    =
-   33|      1|        ||
+   33|       |        ||
    34|      0|    {
    35|      0|        let mut countdown = 0;
    36|      0|        if is_false {

tests/ui/borrowck/borrowck-vec-pattern-nesting.rs

@@ -8,6 +8,7 @@ fn a() {
         //~^ NOTE `vec[_]` is borrowed here
             vec[0] = Box::new(4); //~ ERROR cannot assign
             //~^ NOTE `vec[_]` is assigned to here
+            //~| NOTE in this expansion of desugaring of drop and replace
             _a.use_ref();
             //~^ NOTE borrow later used here
         }
@@ -22,6 +23,7 @@ fn b() {
         //~^ `vec[_]` is borrowed here
             vec[0] = Box::new(4); //~ ERROR cannot assign
             //~^ NOTE `vec[_]` is assigned to here
+            //~| NOTE in this expansion of desugaring of drop and replace
             _b.use_ref();
             //~^ NOTE borrow later used here
         }

tests/ui/borrowck/borrowck-vec-pattern-nesting.stderr

@@ -6,24 +6,24 @@ LL |         [box ref _a, _, _] => {
 LL |
 LL |             vec[0] = Box::new(4);
    |             ^^^^^^ `vec[_]` is assigned to here but it was already borrowed
-LL |
+...
 LL |             _a.use_ref();
    |             ------------ borrow later used here
 
 error[E0506]: cannot assign to `vec[_]` because it is borrowed
-  --> $DIR/borrowck-vec-pattern-nesting.rs:23:13
+  --> $DIR/borrowck-vec-pattern-nesting.rs:24:13
    |
 LL |         &mut [ref _b @ ..] => {
    |               ------ `vec[_]` is borrowed here
 LL |
 LL |             vec[0] = Box::new(4);
    |             ^^^^^^ `vec[_]` is assigned to here but it was already borrowed
-LL |
+...
 LL |             _b.use_ref();
    |             ------------ borrow later used here
 
 error[E0508]: cannot move out of type `[Box<isize>]`, a non-copy slice
-  --> $DIR/borrowck-vec-pattern-nesting.rs:34:11
+  --> $DIR/borrowck-vec-pattern-nesting.rs:36:11
    |
 LL |     match vec {
    |           ^^^ cannot move out of here
@@ -41,7 +41,7 @@ LL +         [_a,
    |
 
 error[E0508]: cannot move out of type `[Box<isize>]`, a non-copy slice
-  --> $DIR/borrowck-vec-pattern-nesting.rs:46:13
+  --> $DIR/borrowck-vec-pattern-nesting.rs:48:13
    |
 LL |     let a = vec[0];
    |             ^^^^^^
@@ -55,7 +55,7 @@ LL |     let a = &vec[0];
    |             +
 
 error[E0508]: cannot move out of type `[Box<isize>]`, a non-copy slice
-  --> $DIR/borrowck-vec-pattern-nesting.rs:55:11
+  --> $DIR/borrowck-vec-pattern-nesting.rs:57:11
    |
 LL |     match vec {
    |           ^^^ cannot move out of here
@@ -73,7 +73,7 @@ LL +         [
    |
 
 error[E0508]: cannot move out of type `[Box<isize>]`, a non-copy slice
-  --> $DIR/borrowck-vec-pattern-nesting.rs:65:13
+  --> $DIR/borrowck-vec-pattern-nesting.rs:67:13
    |
 LL |     let a = vec[0];
    |             ^^^^^^
@@ -87,7 +87,7 @@ LL |     let a = &vec[0];
    |             +
 
 error[E0508]: cannot move out of type `[Box<isize>]`, a non-copy slice
-  --> $DIR/borrowck-vec-pattern-nesting.rs:74:11
+  --> $DIR/borrowck-vec-pattern-nesting.rs:76:11
    |
 LL |     match vec {
    |           ^^^ cannot move out of here
@@ -106,7 +106,7 @@ LL +         [_a, _b, _c] => {}
    |
 
 error[E0508]: cannot move out of type `[Box<isize>]`, a non-copy slice
-  --> $DIR/borrowck-vec-pattern-nesting.rs:85:13
+  --> $DIR/borrowck-vec-pattern-nesting.rs:87:13
    |
 LL |     let a = vec[0];
    |             ^^^^^^

tests/ui/borrowck/issue-45199.rs

@@ -5,6 +5,7 @@ fn test_drop_replace() {
     b = Box::new(1);    //~ NOTE first assignment
     b = Box::new(2);    //~ ERROR cannot assign twice to immutable variable `b`
                         //~| NOTE cannot assign twice to immutable
+                        //~| NOTE in this expansion of desugaring of drop and replace
 }
 
 fn test_call() {
@@ -13,12 +14,14 @@ fn test_call() {
                             //~| SUGGESTION mut b
     b = Box::new(2);        //~ ERROR cannot assign twice to immutable variable `b`
                             //~| NOTE cannot assign twice to immutable
+                            //~| NOTE in this expansion of desugaring of drop and replace
 }
 
 fn test_args(b: Box<i32>) {  //~ HELP consider making this binding mutable
                                 //~| SUGGESTION mut b
     b = Box::new(2);            //~ ERROR cannot assign to immutable argument `b`
                                 //~| NOTE cannot assign to immutable argument
+                                //~| NOTE in this expansion of desugaring of drop and replace
 }
 
 fn main() {}

tests/ui/borrowck/issue-45199.stderr

@@ -10,7 +10,7 @@ LL |     b = Box::new(2);
    |     ^ cannot assign twice to immutable variable
 
 error[E0384]: cannot assign twice to immutable variable `b`
-  --> $DIR/issue-45199.rs:14:5
+  --> $DIR/issue-45199.rs:15:5
    |
 LL |     let b = Box::new(1);
    |         -
@@ -22,7 +22,7 @@ LL |     b = Box::new(2);
    |     ^ cannot assign twice to immutable variable
 
 error[E0384]: cannot assign to immutable argument `b`
-  --> $DIR/issue-45199.rs:20:5
+  --> $DIR/issue-45199.rs:22:5
    |
 LL | fn test_args(b: Box<i32>) {
    |              - help: consider making this binding mutable: `mut b`

tests/ui/borrowck/issue-58776-borrowck-scans-children.rs

@@ -5,7 +5,6 @@ fn main() {
     greeting = "DEALLOCATED".to_string();
     //~^ ERROR cannot assign
     drop(greeting);
-    //~^ ERROR cannot move
 
     println!("thread result: {:?}", res);
 }

tests/ui/borrowck/issue-58776-borrowck-scans-children.stderr

@@ -12,21 +12,6 @@ LL |     greeting = "DEALLOCATED".to_string();
 LL |     println!("thread result: {:?}", res);
    |                                     --- borrow later used here
 
-error[E0505]: cannot move out of `greeting` because it is borrowed
+error: aborting due to previous error
-  --> $DIR/issue-58776-borrowck-scans-children.rs:7:10
-   |
-LL |     let res = (|| (|| &greeting)())();
-   |                --      -------- borrow occurs due to use in closure
-   |                |
-   |                borrow of `greeting` occurs here
-...
-LL |     drop(greeting);
-   |          ^^^^^^^^ move out of `greeting` occurs here
-...
-LL |     println!("thread result: {:?}", res);
-   |                                     --- borrow later used here
 
-error: aborting due to 2 previous errors
+For more information about this error, try `rustc --explain E0506`.
-
-Some errors have detailed explanations: E0505, E0506.
-For more information about an error, try `rustc --explain E0505`.

tests/ui/liveness/liveness-assign/liveness-assign-imm-local-with-drop.rs

@@ -5,6 +5,7 @@ fn test() {
     drop(b);
     b = Box::new(2); //~ ERROR cannot assign twice to immutable variable `b`
                      //~| NOTE cannot assign twice to immutable
+                     //~| NOTE in this expansion of desugaring of drop and replace
     drop(b);
 }