[clang-tidy] `bugprone-use-after-move`: Don't warn on self-moves.

Reviewed By: sammccall, njames93

Differential Revision: https://reviews.llvm.org/D126853

clang-tools-extra/clang-tidy/bugprone/UseAfterMoveCheck.cpp

@@ -158,9 +158,12 @@ bool UseAfterMoveFinder::findInternal(const CFGBlock *Block,
 
   // Ignore all reinitializations where the move potentially comes after the
   // reinit.
+  // If `Reinit` is identical to `MovingCall`, we're looking at a move-to-self
+  // (e.g. `a = std::move(a)`). Count these as reinitializations.
   llvm::SmallVector<const Stmt *, 1> ReinitsToDelete;
   for (const Stmt *Reinit : Reinits) {
-    if (MovingCall && Sequence->potentiallyAfter(MovingCall, Reinit))
+    if (MovingCall && Reinit != MovingCall &&
+        Sequence->potentiallyAfter(MovingCall, Reinit))
       ReinitsToDelete.push_back(Reinit);
   }
   for (const Stmt *Reinit : ReinitsToDelete) {

clang-tools-extra/docs/ReleaseNotes.rst

@@ -207,12 +207,14 @@ Changes in existing checks
 
 - Fixed a crash in :doc:`performance-unnecessary-value-param
   <clang-tidy/checks/readability-suspicious-call-argument>` when the specialization
-  template has an unnecessary value paramter. Removed the fix for a template.
+  template has an unnecessary value parameter. Removed the fix for a template.
 
-- Fixed a bug in :doc:`bugprone-use-after-move
-  <clang-tidy/checks/bugprone-use-after-move>` where a move in a lambda capture
-  was treated as if it happened within the body of the lambda, not within the
-  function that defines the lambda.
+- Fixed bugs in :doc:`bugprone-use-after-move
+  <clang-tidy/checks/bugprone-use-after-move>`:
+  - Treat a move in a lambda capture as happening in the function that defines
+    the lambda, not within the body of the lambda (as we were previously doing
+    erroneously).
+  - Don't emit an erroneous warning on self-moves.
 
 Removed checks
 ^^^^^^^^^^^^^^

clang-tools-extra/test/clang-tidy/checkers/bugprone-use-after-move.cpp

@@ -152,6 +152,13 @@ void simple() {
   // CHECK-NOTES: [[@LINE-3]]:15: note: move occurred here
 }
 
+// Don't flag a move-to-self.
+void selfMove() {
+  A a;
+  a = std::move(a);
+  a.foo();
+}
+
 // A warning should only be emitted for one use-after-move.
 void onlyFlagOneUseAfterMove() {
   A a;