Rollup merge of rust-lang#111952 - cjgillot:drop-replace, r=WaffleLapkin

Remove DesugaringKind::Replace.

A simple boolean flag is enough.

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -1635,34 +1635,6 @@ 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/mutability_errors.rs

@@ -641,13 +641,8 @@ 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 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 };
+            let mut v = V { assign_span: span, err, ty, suggested: false };
             v.visit_body(body);
             if !v.suggested {
                 err.help(format!(

compiler/rustc_borrowck/src/invalidation.rs

@@ -112,11 +112,13 @@ impl<'cx, 'tcx> Visitor<'tcx> for InvalidationGenerator<'cx, 'tcx> {
             TerminatorKind::SwitchInt { discr, targets: _ } => {
                 self.consume_operand(location, discr);
             }
-            TerminatorKind::Drop { place: drop_place, target: _, unwind: _ } => {
+            TerminatorKind::Drop { place: drop_place, target: _, unwind: _, replace } => {
+                let write_kind =
+                    if *replace { WriteKind::Replace } else { WriteKind::StorageDeadOrDrop };
                 self.access_place(
                     location,
                     *drop_place,
-                    (AccessDepth::Drop, Write(WriteKind::StorageDeadOrDrop)),
+                    (AccessDepth::Drop, Write(write_kind)),
                     LocalMutationIsAllowed::Yes,
                 );
             }

compiler/rustc_borrowck/src/lib.rs

@@ -685,17 +685,19 @@ impl<'cx, 'tcx> rustc_mir_dataflow::ResultsVisitor<'cx, 'tcx> for MirBorrowckCtx
             TerminatorKind::SwitchInt { discr, targets: _ } => {
                 self.consume_operand(loc, (discr, span), flow_state);
             }
-            TerminatorKind::Drop { place, target: _, unwind: _ } => {
+            TerminatorKind::Drop { place, target: _, unwind: _, replace } => {
                 debug!(
                     "visit_terminator_drop \
                      loc: {:?} term: {:?} place: {:?} span: {:?}",
                     loc, term, place, span
                 );
 
+                let write_kind =
+                    if *replace { WriteKind::Replace } else { WriteKind::StorageDeadOrDrop };
                 self.access_place(
                     loc,
                     (*place, span),
-                    (AccessDepth::Drop, Write(WriteKind::StorageDeadOrDrop)),
+                    (AccessDepth::Drop, Write(write_kind)),
                     LocalMutationIsAllowed::Yes,
                     flow_state,
                 );
@@ -885,6 +887,7 @@ enum ReadKind {
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 enum WriteKind {
     StorageDeadOrDrop,
+    Replace,
     MutableBorrow(BorrowKind),
     Mutate,
     Move,
@@ -1132,13 +1135,21 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                             this.buffer_error(err);
                         }
                         WriteKind::StorageDeadOrDrop => this
-                            .report_storage_dead_or_drop_of_borrowed(location, place_span, borrow),
+                            .report_borrowed_value_does_not_live_long_enough(
+                                location,
+                                borrow,
+                                place_span,
+                                Some(WriteKind::StorageDeadOrDrop),
+                            ),
                         WriteKind::Mutate => {
                             this.report_illegal_mutation_of_borrowed(location, place_span, borrow)
                         }
                         WriteKind::Move => {
                             this.report_move_out_while_borrowed(location, place_span, borrow)
                         }
+                        WriteKind::Replace => {
+                            this.report_illegal_mutation_of_borrowed(location, place_span, borrow)
+                        }
                     }
                     Control::Break
                 }
@@ -1982,12 +1993,14 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 
             Reservation(
                 WriteKind::Move
+                | WriteKind::Replace
                 | WriteKind::StorageDeadOrDrop
                 | WriteKind::MutableBorrow(BorrowKind::Shared)
                 | WriteKind::MutableBorrow(BorrowKind::Shallow),
             )
             | Write(
                 WriteKind::Move
+                | WriteKind::Replace
                 | WriteKind::StorageDeadOrDrop
                 | WriteKind::MutableBorrow(BorrowKind::Shared)
                 | WriteKind::MutableBorrow(BorrowKind::Shallow),

compiler/rustc_codegen_cranelift/src/base.rs

@@ -473,7 +473,7 @@ fn codegen_fn_body(fx: &mut FunctionCx<'_, '_, '_>, start_block: Block) {
             | TerminatorKind::GeneratorDrop => {
                 bug!("shouldn't exist at codegen {:?}", bb_data.terminator());
             }
-            TerminatorKind::Drop { place, target, unwind: _ } => {
+            TerminatorKind::Drop { place, target, unwind: _, replace: _ } => {
                 let drop_place = codegen_place(fx, *place);
                 crate::abi::codegen_drop(fx, source_info, drop_place);
 

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -1256,7 +1256,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 MergingSucc::False
             }
 
-            mir::TerminatorKind::Drop { place, target, unwind } => {
+            mir::TerminatorKind::Drop { place, target, unwind, replace: _ } => {
                 self.codegen_drop_terminator(helper, bx, place, target, unwind, mergeable_succ())
             }
 

compiler/rustc_const_eval/src/interpret/terminator.rs

@@ -114,7 +114,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 }
             }
 
-            Drop { place, target, unwind } => {
+            Drop { place, target, unwind, replace: _ } => {
                 let frame = self.frame();
                 let ty = place.ty(&frame.body.local_decls, *self.tcx).ty;
                 let ty = self.subst_from_frame_and_normalize_erasing_regions(frame, ty)?;

compiler/rustc_middle/src/mir/syntax.rs

@@ -603,7 +603,11 @@ pub enum TerminatorKind<'tcx> {
     /// > The drop glue is executed if, among all statements executed within this `Body`, an assignment to
     /// > the place or one of its "parents" occurred more recently than a move out of it. This does not
     /// > consider indirect assignments.
-    Drop { place: Place<'tcx>, target: BasicBlock, unwind: UnwindAction },
+    ///
+    /// The `replace` flag indicates whether this terminator was created as part of an assignment.
+    /// This should only be used for diagnostic purposes, and does not have any operational
+    /// meaning.
+    Drop { place: Place<'tcx>, target: BasicBlock, unwind: UnwindAction, replace: bool },
 
     /// Roughly speaking, evaluates the `func` operand and the arguments, and starts execution of
     /// the referred to function. The operand types must match the argument types of the function.

compiler/rustc_middle/src/mir/visit.rs

@@ -504,6 +504,7 @@ macro_rules! make_mir_visitor {
                         place,
                         target: _,
                         unwind: _,
+                        replace: _,
                     } => {
                         self.visit_place(
                             place,

compiler/rustc_mir_build/src/build/custom/parse/instruction.rs

@@ -57,6 +57,7 @@ impl<'tcx, 'body> ParseCtxt<'tcx, 'body> {
                     place: self.parse_place(args[0])?,
                     target: self.parse_block(args[1])?,
                     unwind: UnwindAction::Continue,
+                    replace: false,
                 })
             },
             @call("mir_call", args) => {

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

@@ -725,6 +725,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                         place: to_drop,
                         target: success,
                         unwind: UnwindAction::Continue,
+                        replace: false,
                     },
                 );
                 this.diverge_from(block);

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::{DesugaringKind, Span, DUMMY_SP};
+use rustc_span::{Span, DUMMY_SP};
 
 #[derive(Debug)]
 pub struct Scopes<'tcx> {
@@ -371,6 +371,7 @@ impl DropTree {
                         // The caller will handle this if needed.
                         unwind: UnwindAction::Terminate,
                         place: drop_data.0.local.into(),
+                        replace: false,
                     };
                     cfg.terminate(block, drop_data.0.source_info, terminator);
                 }
@@ -1128,9 +1129,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         place: Place<'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);
 
         // create the new block for the assignment
@@ -1148,6 +1146,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 place,
                 target: assign,
                 unwind: UnwindAction::Cleanup(assign_unwind),
+                replace: true,
             },
         );
         self.diverge_from(block);
@@ -1261,6 +1260,7 @@ fn build_scope_drops<'tcx>(
                         place: local.into(),
                         target: next,
                         unwind: UnwindAction::Continue,
+                        replace: false,
                     },
                 );
                 block = next;

compiler/rustc_mir_dataflow/src/elaborate_drops.rs

@@ -237,6 +237,7 @@ where
                         place: self.place,
                         target: self.succ,
                         unwind: self.unwind.into_action(),
+                        replace: false,
                     },
                 );
             }
@@ -719,6 +720,7 @@ where
                 place: tcx.mk_place_deref(ptr),
                 target: loop_block,
                 unwind: unwind.into_action(),
+                replace: false,
             },
         );
 
@@ -963,8 +965,12 @@ where
     }
 
     fn drop_block(&mut self, target: BasicBlock, unwind: Unwind) -> BasicBlock {
-        let block =
-            TerminatorKind::Drop { place: self.place, target, unwind: unwind.into_action() };
+        let block = TerminatorKind::Drop {
+            place: self.place,
+            target,
+            unwind: unwind.into_action(),
+            replace: false,
+        };
         self.new_block(unwind, block)
     }
 

compiler/rustc_mir_dataflow/src/framework/direction.rs

@@ -479,7 +479,7 @@ impl Direction for Forward {
             Goto { target } => propagate(target, exit_state),
 
             Assert { target, unwind, expected: _, msg: _, cond: _ }
-            | Drop { target, unwind, place: _ }
+            | Drop { target, unwind, place: _, replace: _ }
             | FalseUnwind { real_target: target, unwind } => {
                 if let UnwindAction::Cleanup(unwind) = unwind {
                     propagate(unwind, exit_state);

compiler/rustc_mir_transform/src/add_moves_for_packed_drops.rs

@@ -80,7 +80,7 @@ fn add_move_for_packed_drop<'tcx>(
     is_cleanup: bool,
 ) {
     debug!("add_move_for_packed_drop({:?} @ {:?})", terminator, loc);
-    let TerminatorKind::Drop { ref place, target, unwind } = terminator.kind else {
+    let TerminatorKind::Drop { ref place, target, unwind, replace } = terminator.kind else {
         unreachable!();
     };
 
@@ -98,6 +98,11 @@ fn add_move_for_packed_drop<'tcx>(
     patch.add_assign(loc, Place::from(temp), Rvalue::Use(Operand::Move(*place)));
     patch.patch_terminator(
         loc.block,
-        TerminatorKind::Drop { place: Place::from(temp), target: storage_dead_block, unwind },
+        TerminatorKind::Drop {
+            place: Place::from(temp),
+            target: storage_dead_block,
+            unwind,
+            replace,
+        },
     );
 }

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::{DesugaringKind, Span};
+use rustc_span::Span;
 use rustc_target::abi::{FieldIdx, VariantIdx};
 use std::fmt;
 
@@ -401,7 +401,7 @@ impl<'b, 'tcx> ElaborateDropsCtxt<'b, 'tcx> {
             let terminator = data.terminator();
 
             match terminator.kind {
-                TerminatorKind::Drop { mut place, target, unwind } => {
+                TerminatorKind::Drop { mut place, target, unwind, replace } => {
                     if let Some(new_place) = self.un_derefer.derefer(place.as_ref(), self.body) {
                         place = new_place;
                     }
@@ -434,10 +434,7 @@ impl<'b, 'tcx> ElaborateDropsCtxt<'b, 'tcx> {
                             )
                         }
                         LookupResult::Parent(..) => {
-                            if !matches!(
-                                terminator.source_info.span.desugaring_kind(),
-                                Some(DesugaringKind::Replace),
-                            ) {
+                            if !replace {
                                 self.tcx.sess.delay_span_bug(
                                     terminator.source_info.span,
                                     format!("drop of untracked value {:?}", bb),

compiler/rustc_mir_transform/src/generator.rs

@@ -1045,7 +1045,10 @@ fn elaborate_generator_drops<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 
     for (block, block_data) in body.basic_blocks.iter_enumerated() {
         let (target, unwind, source_info) = match block_data.terminator() {
-            Terminator { source_info, kind: TerminatorKind::Drop { place, target, unwind } } => {
+            Terminator {
+                source_info,
+                kind: TerminatorKind::Drop { place, target, unwind, replace: _ },
+            } => {
                 if let Some(local) = place.as_local() {
                     if local == SELF_ARG {
                         (target, unwind, source_info)
@@ -1304,6 +1307,7 @@ fn insert_clean_drop(body: &mut Body<'_>) -> BasicBlock {
         place: Place::from(SELF_ARG),
         target: return_block,
         unwind: UnwindAction::Continue,
+        replace: false,
     };
     let source_info = SourceInfo::outermost(body.span);
 

compiler/rustc_mir_transform/src/inline.rs

@@ -449,16 +449,16 @@ impl<'tcx> Inliner<'tcx> {
             checker.visit_basic_block_data(bb, blk);
 
             let term = blk.terminator();
-            if let TerminatorKind::Drop { ref place, target, unwind } = term.kind {
+            if let TerminatorKind::Drop { ref place, target, unwind, replace: _ } = term.kind {
                 work_list.push(target);
 
                 // If the place doesn't actually need dropping, treat it like a regular goto.
                 let ty = callsite
                     .callee
                     .subst_mir(self.tcx, ty::EarlyBinder(&place.ty(callee_body, tcx).ty));
                 if ty.needs_drop(tcx, self.param_env) && let UnwindAction::Cleanup(unwind) = unwind {
-                        work_list.push(unwind);
-                    }
+                    work_list.push(unwind);
+                }
             } else if callee_attrs.instruction_set != self.codegen_fn_attrs.instruction_set
                 && matches!(term.kind, TerminatorKind::InlineAsm { .. })
             {

compiler/rustc_mir_transform/src/shim.rs

@@ -544,6 +544,7 @@ impl<'tcx> CloneShimBuilder<'tcx> {
                     place: dest_field,
                     target: unwind,
                     unwind: UnwindAction::Terminate,
+                    replace: false,
                 },
                 true,
             );
@@ -800,6 +801,7 @@ fn build_call_shim<'tcx>(
                 place: rcvr_place(),
                 target: BasicBlock::new(2),
                 unwind: UnwindAction::Continue,
+                replace: false,
             },
             false,
         );
@@ -815,6 +817,7 @@ fn build_call_shim<'tcx>(
                 place: rcvr_place(),
                 target: BasicBlock::new(4),
                 unwind: UnwindAction::Terminate,
+                replace: false,
             },
             true,
         );