Introduce a no-op PlaceMention statement for `let _ =`.

5 files changed, 10 insertions, 2 deletions

diff --git a/compiler/rustc_borrowck/src/dataflow.rs b/compiler/rustc_borrowck/src/dataflow.rs
index d2574aa58c2..0762987e229 100644
--- a/compiler/rustc_borrowck/src/dataflow.rs
+++ b/compiler/rustc_borrowck/src/dataflow.rs
@@ -390,6 +390,7 @@ impl<'tcx> rustc_mir_dataflow::GenKillAnalysis<'tcx> for Borrows<'_, 'tcx> {
             | mir::StatementKind::Deinit(..)
             | mir::StatementKind::StorageLive(..)
             | mir::StatementKind::Retag { .. }
+            | mir::StatementKind::PlaceMention(..)
             | mir::StatementKind::AscribeUserType(..)
             | mir::StatementKind::Coverage(..)
             | mir::StatementKind::Intrinsic(..)
diff --git a/compiler/rustc_borrowck/src/def_use.rs b/compiler/rustc_borrowck/src/def_use.rs
index 8e62a0198be..c67411c4784 100644
--- a/compiler/rustc_borrowck/src/def_use.rs
+++ b/compiler/rustc_borrowck/src/def_use.rs
@@ -73,7 +73,7 @@ pub fn categorize(context: PlaceContext) -> Option<DefUse> {
             Some(DefUse::Drop),
 
         // Debug info is neither def nor use.
-        PlaceContext::NonUse(NonUseContext::VarDebugInfo) => None,
+        PlaceContext::NonUse(NonUseContext::PlaceMention | NonUseContext::VarDebugInfo) => None,
 
         PlaceContext::MutatingUse(MutatingUseContext::Deinit | MutatingUseContext::SetDiscriminant) => {
             bug!("These statements are not allowed in this MIR phase")
diff --git a/compiler/rustc_borrowck/src/invalidation.rs b/compiler/rustc_borrowck/src/invalidation.rs
index 1006a047cce..a71c4163286 100644
--- a/compiler/rustc_borrowck/src/invalidation.rs
+++ b/compiler/rustc_borrowck/src/invalidation.rs
@@ -79,6 +79,8 @@ impl<'cx, 'tcx> Visitor<'tcx> for InvalidationGenerator<'cx, 'tcx> {
             }
             // Only relevant for mir typeck
             StatementKind::AscribeUserType(..)
+            // Only relevant for unsafeck
+            | StatementKind::PlaceMention(..)
             // Doesn't have any language semantics
             | StatementKind::Coverage(..)
             // Does not actually affect borrowck
diff --git a/compiler/rustc_borrowck/src/lib.rs b/compiler/rustc_borrowck/src/lib.rs
index 92acd755509..f84a4691d32 100644
--- a/compiler/rustc_borrowck/src/lib.rs
+++ b/compiler/rustc_borrowck/src/lib.rs
@@ -690,6 +690,8 @@ impl<'cx, 'tcx> rustc_mir_dataflow::ResultsVisitor<'cx, 'tcx> for MirBorrowckCtx
             }
             // Only relevant for mir typeck
             StatementKind::AscribeUserType(..)
+            // Only relevant for unsafeck
+            | StatementKind::PlaceMention(..)
             // Doesn't have any language semantics
             | StatementKind::Coverage(..)
             // These do not actually affect borrowck
diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs
index d85e058bb20..3919c4793a0 100644
--- a/compiler/rustc_borrowck/src/type_check/mod.rs
+++ b/compiler/rustc_borrowck/src/type_check/mod.rs
@@ -772,7 +772,9 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
 
         match context {
             PlaceContext::MutatingUse(_) => ty::Invariant,
-            PlaceContext::NonUse(StorageDead | StorageLive | VarDebugInfo) => ty::Invariant,
+            PlaceContext::NonUse(StorageDead | StorageLive | PlaceMention | VarDebugInfo) => {
+                ty::Invariant
+            }
             PlaceContext::NonMutatingUse(
                 Inspect | Copy | Move | SharedBorrow | ShallowBorrow | UniqueBorrow | AddressOf
                 | Projection,
@@ -1282,6 +1284,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             | StatementKind::Retag { .. }
             | StatementKind::Coverage(..)
             | StatementKind::ConstEvalCounter
+            | StatementKind::PlaceMention(..)
             | StatementKind::Nop => {}
             StatementKind::Deinit(..) | StatementKind::SetDiscriminant { .. } => {
                 bug!("Statement not allowed in this MIR phase")