[clang-tidy] Fix `readability-const-return-type` for pure virtual function.

It cannot match a `pure virtual function`. This patch fixes this behavior.

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D116439

clang-tools-extra/clang-tidy/readability/ConstReturnTypeCheck.cpp

@@ -97,7 +97,9 @@ void ConstReturnTypeCheck::registerMatchers(MatchFinder *Finder) {
   // Find all function definitions for which the return types are `const`
   // qualified.
   Finder->addMatcher(
-      functionDecl(returns(isConstQualified()), isDefinition()).bind("func"),
+      functionDecl(returns(isConstQualified()),
+                   anyOf(isDefinition(), cxxMethodDecl(isPure())))
+          .bind("func"),
       this);
 }
 
@@ -115,6 +117,12 @@ void ConstReturnTypeCheck::check(const MatchFinder::MatchResult &Result) {
         << Def->getReturnType();
     if (CR.ConstRange.isValid())
       Diagnostic << CR.ConstRange;
+
+    // Do not propose fixes for virtual function.
+    const auto *Method = dyn_cast<CXXMethodDecl>(Def);
+    if (Method && Method->isVirtual())
+      return;
+
     for (auto &Hint : CR.Hints)
       Diagnostic << Hint;
   }

clang-tools-extra/docs/ReleaseNotes.rst

@@ -112,6 +112,10 @@ Changes in existing checks
 - 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
 
+- Fixed a crash in :doc:`readability-const-return-type
+  <clang-tidy/checks/readability-const-return-type>` when a pure virtual function
+  overrided has a const return type. Removed the fix for a virtual function.
+
 Removed checks
 ^^^^^^^^^^^^^^
 

clang-tools-extra/test/clang-tidy/checkers/readability-const-return-type.cpp

@@ -271,3 +271,17 @@ const int n14();
 
 int **const * n_multiple_ptr();
 int *const & n_pointer_ref();
+
+class PVBase {
+public:
+  virtual const int getC() = 0;
+  // CHECK-MESSAGES: [[@LINE-1]]:3: warning: return type 'const int' is 'const'-qualified at the top level, which may reduce code readability without improving const correctness
+  // CHECK-NOT-FIXES: virtual int getC() = 0;
+};
+
+class PVDerive : public PVBase {
+public:
+  const int getC() { return 1; }
+  // CHECK-MESSAGES: [[@LINE-1]]:3: warning: return type 'const int' is 'const'-qualified at the top level, which may reduce code readability without improving const correctness
+  // CHECK-NOT-FIXES: int getC() { return 1; }
+};