[clang-tools-extra] `clang-tidy`: Make `bugprone-unhandled-self-assignment` check more general (PR #147066)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang-tidy

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

Author: Andrey Karlov (negativ)

<details>
<summary>Changes</summary>

This change enhances the `bugprone-unhandled-self-assignment` checker by adding an additional matcher that generalizes the copy-and-swap idiom pattern detection.

# What Changed

Added a new matcher that checks for:
- An instance of the current class being created in operator= (regardless of constructor arguments)
- That instance being passed to a `swap` function call

# Problem Solved
This fix reduces false positives in PMR-like scenarios where "extended" constructors are used (typically taking an additional allocator argument). The checker now properly recognizes copy-and-swap implementations that use extended copy/move constructors instead of flagging them as unhandled self-assignment cases.

For e.g:
```cpp
T& operator=(const T& other) {
   T tmp{other.internal_data(), get_allocator()};  // Extended constructor
   swap(tmp);
   return *this;
}
```

---
Full diff: https://github.com/llvm/llvm-project/pull/147066.diff


2 Files Affected:

- (modified) clang-tools-extra/clang-tidy/bugprone/UnhandledSelfAssignmentCheck.cpp (+18-1) 
- (modified) clang-tools-extra/test/clang-tidy/checkers/bugprone/unhandled-self-assignment.cpp (+90) 


``````````diff
diff --git a/clang-tools-extra/clang-tidy/bugprone/UnhandledSelfAssignmentCheck.cpp b/clang-tools-extra/clang-tidy/bugprone/UnhandledSelfAssignmentCheck.cpp
index 1f432c4ccc5f0..8307e744a434c 100644
--- a/clang-tools-extra/clang-tidy/bugprone/UnhandledSelfAssignmentCheck.cpp
+++ b/clang-tools-extra/clang-tidy/bugprone/UnhandledSelfAssignmentCheck.cpp
@@ -68,7 +68,23 @@ void UnhandledSelfAssignmentCheck::registerMatchers(MatchFinder *Finder) {
   const auto HasNoNestedSelfAssign =
       cxxMethodDecl(unless(hasDescendant(cxxMemberCallExpr(callee(cxxMethodDecl(
           hasName("operator="), ofClass(equalsBoundNode("class"))))))));
-
+  
+  // Checking that some kind of constructor is called and followed by a `swap`:
+  // T& operator=(const T& other) {
+  //    T tmp{this->internal_data(), some, other, args};
+  //    swap(tmp);
+  //    return *this;
+  // }
+  const auto HasCopyAndSwap = cxxMethodDecl(
+      ofClass(cxxRecordDecl(unless(hasAncestor(classTemplateDecl())))),
+      hasDescendant(
+          stmt(hasDescendant(
+                   varDecl(hasType(cxxRecordDecl(equalsBoundNode("class"))))
+                       .bind("tmp_var")),
+               hasDescendant(callExpr(callee(functionDecl(hasName("swap"))),
+                                      hasAnyArgument(declRefExpr(to(varDecl(
+                                          equalsBoundNode("tmp_var"))))))))));
+    
   DeclarationMatcher AdditionalMatcher = cxxMethodDecl();
   if (WarnOnlyIfThisHasSuspiciousField) {
     // Matcher for standard smart pointers.
@@ -94,6 +110,7 @@ void UnhandledSelfAssignmentCheck::registerMatchers(MatchFinder *Finder) {
                                    HasReferenceParam, HasNoSelfCheck,
                                    unless(HasNonTemplateSelfCopy),
                                    unless(HasTemplateSelfCopy),
+                                   unless(HasCopyAndSwap),
                                    HasNoNestedSelfAssign, AdditionalMatcher)
                          .bind("copyAssignmentOperator"),
                      this);
diff --git a/clang-tools-extra/test/clang-tidy/checkers/bugprone/unhandled-self-assignment.cpp b/clang-tools-extra/test/clang-tidy/checkers/bugprone/unhandled-self-assignment.cpp
index 8610393449f97..f2f61062f883f 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/bugprone/unhandled-self-assignment.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/bugprone/unhandled-self-assignment.cpp
@@ -28,6 +28,13 @@ template <class T>
 class auto_ptr {
 };
 
+namespace pmr {
+    template <typename TYPE = void>
+    class allocator {};
+}
+
+struct allocator_arg_t {} allocator_arg;
+
 } // namespace std
 
 void assert(int expression){};
@@ -540,6 +547,89 @@ class NotACopyAssignmentOperator {
   Uy *getUy() const { return Ptr2; }
 };
 
+// Support "extended" copy/move constructors
+class AllocatorAwareClass {
+  // pointer member to trigger bugprone-unhandled-self-assignment
+  void *foo = nullptr;
+
+  public:
+    using allocator_type = std::pmr::allocator<>;
+
+    AllocatorAwareClass(const AllocatorAwareClass& other) {
+    }
+
+    AllocatorAwareClass(const AllocatorAwareClass& other, const allocator_type& alloc) {
+    }
+
+    AllocatorAwareClass& operator=(const AllocatorAwareClass& other) {
+        AllocatorAwareClass tmp(other, get_allocator());
+        swap(tmp);
+        return *this;
+    }
+
+    void swap(AllocatorAwareClass& other) noexcept {
+    }
+
+    allocator_type get_allocator() const {
+        return allocator_type();
+    }
+};
+
+// Support "extended" copy/move constructors + std::swap
+class AllocatorAwareClassStdSwap {
+  // pointer member to trigger bugprone-unhandled-self-assignment
+  void *foo = nullptr;
+
+  public:
+    using allocator_type = std::pmr::allocator<>;
+
+    AllocatorAwareClassStdSwap(const AllocatorAwareClassStdSwap& other) {
+    }
+
+    AllocatorAwareClassStdSwap(const AllocatorAwareClassStdSwap& other, const allocator_type& alloc) {
+    }
+
+    AllocatorAwareClassStdSwap& operator=(const AllocatorAwareClassStdSwap& other) {
+        using std::swap;
+        
+        AllocatorAwareClassStdSwap tmp(other, get_allocator());
+        swap(*this, tmp);
+        return *this;
+    }
+
+    allocator_type get_allocator() const {
+        return allocator_type();
+    }
+};
+
+// Support "extended" copy/move constructors + ADL swap
+class AllocatorAwareClassAdlSwap {
+  // pointer member to trigger bugprone-unhandled-self-assignment
+  void *foo = nullptr;
+
+  public:
+    using allocator_type = std::pmr::allocator<>;
+
+    AllocatorAwareClassAdlSwap(const AllocatorAwareClassAdlSwap& other) {
+    }
+
+    AllocatorAwareClassAdlSwap(const AllocatorAwareClassAdlSwap& other, const allocator_type& alloc) {
+    }
+
+    AllocatorAwareClassAdlSwap& operator=(const AllocatorAwareClassAdlSwap& other) {
+        AllocatorAwareClassAdlSwap tmp(other, get_allocator());
+        swap(*this, tmp);
+        return *this;
+    }
+
+    allocator_type get_allocator() const {
+        return allocator_type();
+    }
+    
+    friend void swap(AllocatorAwareClassAdlSwap&, AllocatorAwareClassAdlSwap&) {
+    }
+};
+
 ///////////////////////////////////////////////////////////////////
 /// Test cases which should be caught by the check.
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/147066