Auto merge of #112145 - wesleywiser:backport_112070, r=Mark-Simulacrum 1.70.0

Backport of #112070

Backports #112070 to stable

r? `@Mark-Simulacrum`

9 files changed, 14 insertions, 19 deletions

diff --git a/compiler/rustc_borrowck/src/def_use.rs b/compiler/rustc_borrowck/src/def_use.rs
index 9e9f0b4b4ad..6deb4e361bc 100644
--- a/compiler/rustc_borrowck/src/def_use.rs
+++ b/compiler/rustc_borrowck/src/def_use.rs
@@ -50,7 +50,6 @@ pub fn categorize(context: PlaceContext) -> Option<DefUse> {
         PlaceContext::MutatingUse(MutatingUseContext::Borrow) |
         PlaceContext::NonMutatingUse(NonMutatingUseContext::SharedBorrow) |
         PlaceContext::NonMutatingUse(NonMutatingUseContext::ShallowBorrow) |
-        PlaceContext::NonMutatingUse(NonMutatingUseContext::UniqueBorrow) |
 
         PlaceContext::MutatingUse(MutatingUseContext::AddressOf) |
         PlaceContext::NonMutatingUse(NonMutatingUseContext::AddressOf) |
diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs
index 375eca1b29d..2f10e30bec2 100644
--- a/compiler/rustc_borrowck/src/type_check/mod.rs
+++ b/compiler/rustc_borrowck/src/type_check/mod.rs
@@ -775,9 +775,10 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
                 ty::Invariant
             }
             PlaceContext::NonMutatingUse(
-                Inspect | Copy | Move | SharedBorrow | ShallowBorrow | UniqueBorrow | AddressOf
-                | Projection,
-            ) => ty::Covariant,
+                Inspect | Copy | Move | SharedBorrow | ShallowBorrow | AddressOf | Projection
+            ) => {
+                ty::Covariant
+            },
             PlaceContext::NonUse(AscribeUserTy) => ty::Covariant,
         }
     }
diff --git a/compiler/rustc_codegen_ssa/src/mir/analyze.rs b/compiler/rustc_codegen_ssa/src/mir/analyze.rs
index 115a41050d2..f43f1d64adb 100644
--- a/compiler/rustc_codegen_ssa/src/mir/analyze.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/analyze.rs
@@ -232,7 +232,6 @@ impl<'mir, 'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> Visitor<'tcx>
             | PlaceContext::NonMutatingUse(
                 NonMutatingUseContext::Inspect
                 | NonMutatingUseContext::SharedBorrow
-                | NonMutatingUseContext::UniqueBorrow
                 | NonMutatingUseContext::ShallowBorrow
                 | NonMutatingUseContext::AddressOf
                 | NonMutatingUseContext::Projection,
diff --git a/compiler/rustc_const_eval/src/transform/check_consts/check.rs b/compiler/rustc_const_eval/src/transform/check_consts/check.rs
index 9dad9479053..55080d94f1d 100644
--- a/compiler/rustc_const_eval/src/transform/check_consts/check.rs
+++ b/compiler/rustc_const_eval/src/transform/check_consts/check.rs
@@ -412,9 +412,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                         BorrowKind::Shallow => {
                             PlaceContext::NonMutatingUse(NonMutatingUseContext::ShallowBorrow)
                         }
-                        BorrowKind::Unique => {
-                            PlaceContext::NonMutatingUse(NonMutatingUseContext::UniqueBorrow)
-                        }
+                        BorrowKind::Unique => PlaceContext::MutatingUse(MutatingUseContext::Borrow),
                         BorrowKind::Mut { .. } => {
                             PlaceContext::MutatingUse(MutatingUseContext::Borrow)
                         }
diff --git a/compiler/rustc_middle/src/mir/syntax.rs b/compiler/rustc_middle/src/mir/syntax.rs
index 135889d0da8..93800d48407 100644
--- a/compiler/rustc_middle/src/mir/syntax.rs
+++ b/compiler/rustc_middle/src/mir/syntax.rs
@@ -220,6 +220,11 @@ pub enum BorrowKind {
     /// immutable, but not aliasable. This solves the problem. For
     /// simplicity, we don't give users the way to express this
     /// borrow, it's just used when translating closures.
+    ///
+    // FIXME(#112072): This is wrong. Unique borrows are mutable borrows except
+    // that they do not require their pointee to be marked as a mutable.
+    // They should still be treated as mutable borrows in every other way,
+    // e.g. for variance or overlap checking.
     Unique,
 
     /// Data is mutable and not aliasable.
diff --git a/compiler/rustc_middle/src/mir/visit.rs b/compiler/rustc_middle/src/mir/visit.rs
index 0a9fcd898b9..caa5edc321b 100644
--- a/compiler/rustc_middle/src/mir/visit.rs
+++ b/compiler/rustc_middle/src/mir/visit.rs
@@ -640,8 +640,8 @@ macro_rules! make_mir_visitor {
                             BorrowKind::Shallow => PlaceContext::NonMutatingUse(
                                 NonMutatingUseContext::ShallowBorrow
                             ),
-                            BorrowKind::Unique => PlaceContext::NonMutatingUse(
-                                NonMutatingUseContext::UniqueBorrow
+                            BorrowKind::Unique => PlaceContext::MutatingUse(
+                                MutatingUseContext::Borrow
                             ),
                             BorrowKind::Mut { .. } =>
                                 PlaceContext::MutatingUse(MutatingUseContext::Borrow),
@@ -1247,8 +1247,6 @@ pub enum NonMutatingUseContext {
     SharedBorrow,
     /// Shallow borrow.
     ShallowBorrow,
-    /// Unique borrow.
-    UniqueBorrow,
     /// AddressOf for *const pointer.
     AddressOf,
     /// Used as base for another place, e.g., `x` in `x.y`. Will not mutate the place.
@@ -1324,9 +1322,7 @@ impl PlaceContext {
         matches!(
             self,
             PlaceContext::NonMutatingUse(
-                NonMutatingUseContext::SharedBorrow
-                    | NonMutatingUseContext::ShallowBorrow
-                    | NonMutatingUseContext::UniqueBorrow
+                NonMutatingUseContext::SharedBorrow | NonMutatingUseContext::ShallowBorrow
             ) | PlaceContext::MutatingUse(MutatingUseContext::Borrow)
         )
     }
diff --git a/compiler/rustc_mir_dataflow/src/impls/liveness.rs b/compiler/rustc_mir_dataflow/src/impls/liveness.rs
index bc67aa476f1..1309ea52566 100644
--- a/compiler/rustc_mir_dataflow/src/impls/liveness.rs
+++ b/compiler/rustc_mir_dataflow/src/impls/liveness.rs
@@ -198,8 +198,7 @@ impl DefUse {
                 | NonMutatingUseContext::Inspect
                 | NonMutatingUseContext::Move
                 | NonMutatingUseContext::ShallowBorrow
-                | NonMutatingUseContext::SharedBorrow
-                | NonMutatingUseContext::UniqueBorrow,
+                | NonMutatingUseContext::SharedBorrow,
             ) => Some(DefUse::Use),
 
             PlaceContext::MutatingUse(MutatingUseContext::Projection)
diff --git a/compiler/rustc_mir_transform/src/const_prop.rs b/compiler/rustc_mir_transform/src/const_prop.rs
index c0146e3efb0..1bb45341e8c 100644
--- a/compiler/rustc_mir_transform/src/const_prop.rs
+++ b/compiler/rustc_mir_transform/src/const_prop.rs
@@ -822,7 +822,6 @@ impl Visitor<'_> for CanConstProp {
             // mutation.
             | NonMutatingUse(NonMutatingUseContext::SharedBorrow)
             | NonMutatingUse(NonMutatingUseContext::ShallowBorrow)
-            | NonMutatingUse(NonMutatingUseContext::UniqueBorrow)
             | NonMutatingUse(NonMutatingUseContext::AddressOf)
             | MutatingUse(MutatingUseContext::Borrow)
             | MutatingUse(MutatingUseContext::AddressOf) => {
diff --git a/compiler/rustc_mir_transform/src/copy_prop.rs b/compiler/rustc_mir_transform/src/copy_prop.rs
index c155048c98b..b571215f212 100644
--- a/compiler/rustc_mir_transform/src/copy_prop.rs
+++ b/compiler/rustc_mir_transform/src/copy_prop.rs
@@ -131,7 +131,6 @@ impl<'tcx> MutVisitor<'tcx> for Replacer<'_, 'tcx> {
             PlaceContext::NonMutatingUse(
                 NonMutatingUseContext::SharedBorrow
                 | NonMutatingUseContext::ShallowBorrow
-                | NonMutatingUseContext::UniqueBorrow
                 | NonMutatingUseContext::AddressOf,
             ) => true,
             // For debuginfo, merging locals is ok.