[clang-tools-extra] [clang-tidy] Fix false positives with template in `misc-unconventional-assign-operator` check (PR #143292)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-tools-extra

Author: None (flovent)

<details>
<summary>Changes</summary>

Fix false positives when copy assignment operator function in a template class returns the result of another assignment to `*this`, this check doesn't consider this situation that there will be a `BinaryOperator` for assignment rather than `CXXOperatorCallExpr` since `this`'s type is dependent.

Closes #<!-- -->143237.

---
Full diff: https://github.com/llvm/llvm-project/pull/143292.diff


3 Files Affected:

- (modified) clang-tools-extra/clang-tidy/misc/UnconventionalAssignOperatorCheck.cpp (+5-2) 
- (modified) clang-tools-extra/docs/ReleaseNotes.rst (+5) 
- (modified) clang-tools-extra/test/clang-tidy/checkers/misc/unconventional-assign-operator.cpp (+13) 


``````````diff
diff --git a/clang-tools-extra/clang-tidy/misc/UnconventionalAssignOperatorCheck.cpp b/clang-tools-extra/clang-tidy/misc/UnconventionalAssignOperatorCheck.cpp
index afc4897eeb2ae..3fdaf9239f6af 100644
--- a/clang-tools-extra/clang-tidy/misc/UnconventionalAssignOperatorCheck.cpp
+++ b/clang-tools-extra/clang-tidy/misc/UnconventionalAssignOperatorCheck.cpp
@@ -66,8 +66,11 @@ void UnconventionalAssignOperatorCheck::registerMatchers(
                                 hasArgument(0, cxxThisExpr())),
             cxxOperatorCallExpr(
                 hasOverloadedOperatorName("="),
-                hasArgument(
-                    0, unaryOperator(hasOperatorName("*"),
+                hasArgument(0, unaryOperator(hasOperatorName("*"),
+                                             hasUnaryOperand(cxxThisExpr())))),
+            binaryOperator(
+                hasOperatorName("="),
+                hasLHS(unaryOperator(hasOperatorName("*"),
                                      hasUnaryOperand(cxxThisExpr())))))))));
   const auto IsGoodAssign = cxxMethodDecl(IsAssign, HasGoodReturnType);
 
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index a275d2ccfa004..394e18cd58f84 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -208,6 +208,11 @@ Changes in existing checks
   <clang-tidy/checks/misc/unused-using-decls>` check by fixing false positives
   on ``operator""`` with template parameters.
 
+- Improved :doc:`misc-unconventional-assign-operator
+  <clang-tidy/checks/misc/misc-unconventional-assign-operator>` check by fixing
+  false positives when copy assignment operator function in a template class
+  returns the result of another assignment to ``*this``(``return *this=...``).
+
 - Improved :doc:`misc-use-internal-linkage
   <clang-tidy/checks/misc/use-internal-linkage>` check by fix false positives
   for function or variable in header file which contains macro expansion and
diff --git a/clang-tools-extra/test/clang-tidy/checkers/misc/unconventional-assign-operator.cpp b/clang-tools-extra/test/clang-tidy/checkers/misc/unconventional-assign-operator.cpp
index 74a22a7c083f4..9384d88c38fd0 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/misc/unconventional-assign-operator.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/misc/unconventional-assign-operator.cpp
@@ -163,3 +163,16 @@ struct TemplateTypeAlias {
   Alias3<TypeAlias::Alias> &operator=(double) { return *this; }
   // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: operator=() should return 'TemplateTypeAlias&' [misc-unconventional-assign-operator]
 };
+
+namespace issue143237 {
+template<typename T>
+struct B {
+  explicit B(int) {
+  }
+
+  B& operator=(int n) {
+    // No warning
+    return *this = B(n);
+  }
+};
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/143292