[clang-tidy] Fix PR35468

[xazax.hun]

Summary

Auto return type was not correctly considered by the Unconventional Assign Operator check.

[alexfh]

LG with one comment.

test/clang-tidy/misc-unconventional-assign-operator.cpp

1 ↗

(On Diff #143712)

I'd prefer to add a separate test file for C++17-dependent tests. It would be nice to ensure the rest works fine in C++11.

clang-tools-extra/trunk/clang-tidy/misc/UnconventionalAssignOperatorCheck.cpp

 
 void UnconventionalAssignOperatorCheck::registerMatchers(
     ast_matchers::MatchFinder *Finder) {
   // Only register the matchers for C++; the functionality currently does not
   // provide any benefit to other languages, despite being benign.
   if (!getLangOpts().CPlusPlus)
     return;
 
-  const auto HasGoodReturnType = cxxMethodDecl(returns(
-      lValueReferenceType(pointee(unless(isConstQualified()),
-                                  hasDeclaration(equalsBoundNode("class"))))));
+  const auto HasGoodReturnType = cxxMethodDecl(returns(lValueReferenceType(
+      pointee(unless(isConstQualified()),
+              anyOf(autoType(), hasDeclaration(equalsBoundNode("class")))))));
 
   const auto IsSelf = qualType(
       anyOf(hasDeclaration(equalsBoundNode("class")),
             referenceType(pointee(hasDeclaration(equalsBoundNode("class"))))));
   const auto IsAssign =
       cxxMethodDecl(unless(anyOf(isDeleted(), isPrivate(), isImplicit())),
                     hasName("operator="), ofClass(recordDecl().bind("class")))
           .bind("method");

clang-tools-extra/trunk/test/clang-tidy/misc-unconventional-assign-operator-cxx17.cpp

+// RUN: %check_clang_tidy %s misc-unconventional-assign-operator %t -- -- -std=c++17 -fno-delayed-template-parsing
+
+struct BadModifier {
+  BadModifier& operator=(const BadModifier&) const;
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: operator=() should not be marked 'const'
+};
+
+struct PR35468 {
+  template<typename T> auto &operator=(const T &) {
+    return *this;
+  }
+};