[clang-tidy] Never consider assignments as equivalent in misc-redundant-expression check

FabianWolff · FabianWolff · commit a18634b74fc0 · 2022-04-12T16:03:14.000+02:00
Fixes #35853. Reviewed By: aaron.ballman Differential Revision: https://reviews.llvm.org/D122535
diff --git a/clang-tools-extra/clang-tidy/misc/RedundantExpressionCheck.cpp b/clang-tools-extra/clang-tidy/misc/RedundantExpressionCheck.cpp
@@ -134,6 +134,8 @@ static bool areEquivalentExpr(const Expr *Left, const Expr *Right) {
     return cast<UnaryOperator>(Left)->getOpcode() ==
            cast<UnaryOperator>(Right)->getOpcode();
   case Stmt::BinaryOperatorClass:
+    if (cast<BinaryOperator>(Left)->isAssignmentOp())
+      return false;
     return cast<BinaryOperator>(Left)->getOpcode() ==
            cast<BinaryOperator>(Right)->getOpcode();
   case Stmt::UnaryExprOrTypeTraitExprClass:
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -132,7 +132,7 @@ Changes in existing checks
   the vector is a member of a structure.
 
 - Fixed a false positive in :doc:`readability-non-const-parameter
-  <clang-tidy/checks/readability-non-const-parameter>` when the parameter is referenced by an lvalue
+  <clang-tidy/checks/readability-non-const-parameter>` when the parameter is referenced by an lvalue.
 
 - Fixed a crash in :doc:`readability-const-return-type
   <clang-tidy/checks/readability-const-return-type>` when a pure virtual function
@@ -150,6 +150,9 @@ Changes in existing checks
   Fixed an issue when there was already an initializer in the constructor and
   the check would try to create another initializer for the same member.
 
+- Fixed a false positive in :doc:`misc-redundant-expression <clang-tidy/checks/misc-redundant-expression>`
+  involving assignments in conditions. This fixes `Issue 35853 <https://github.com/llvm/llvm-project/issues/35853>`_.
+
 Removed checks
 ^^^^^^^^^^^^^^
 
diff --git a/clang-tools-extra/test/clang-tidy/checkers/misc-redundant-expression.cpp b/clang-tools-extra/test/clang-tidy/checkers/misc-redundant-expression.cpp
@@ -831,3 +831,15 @@ struct Bar2 {
 };
 
 } // namespace no_crash
+
+int TestAssignSideEffect(int i) {
+  int k = i;
+
+  if ((k = k + 1) != 1 || (k = k + 1) != 2)
+    return 0;
+
+  if ((k = foo(0)) != 1 || (k = foo(0)) != 2)
+    return 1;
+
+  return 2;
+}
