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

[Andrey Karlov via cfe-commits]

================
@@ -69,6 +69,28 @@ void UnhandledSelfAssignmentCheck::registerMatchers(MatchFinder *Finder) {
       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()),
+      hasBody(compoundStmt(
+          hasDescendant(
+              varDecl(hasType(cxxRecordDecl(equalsBoundNode("class"))))
+                  .bind("tmp_var")),
+          hasDescendant(stmt(anyOf(
+              cxxMemberCallExpr(hasArgument(
+                  0, declRefExpr(to(varDecl(equalsBoundNode("tmp_var")))))),
+              callExpr(
+                  callee(functionDecl(hasName("swap"))), argumentCountIs(2),
+                  hasAnyArgument(
+                      declRefExpr(to(varDecl(equalsBoundNode("tmp_var"))))),
+                  hasAnyArgument(unaryOperator(has(cxxThisExpr()),
+                                               hasOperatorName("*"))))))))));
----------------
negativ wrote:

@vbvictor why should we fire a warning for the following code?

```cpp
Thing& operator=(const Thing& other) {
    using std::swap;
    
    Thing tmp{other};
    swap(tmp, *this);
    
    return *this;
}
```
I don't think hardcoding the argument order gives us any real technical benefits (maybe just slightly faster matching) but could cause false-positive warnings on perfectly good code.

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