[clang-tidy] Fix handling of functional cast in google-readability-casting (#71650)

Fix issue with constructor call being interpreted as functional cast and
considered for a replacement
with static cast or being removed as redundant.

Closes #57959

Author: PiotrZSL

clang-tools-extra/clang-tidy/google/AvoidCStyleCastsCheck.cpp

@@ -23,14 +23,16 @@ void AvoidCStyleCastsCheck::registerMatchers(
           // Filter out (EnumType)IntegerLiteral construct, which is generated
           // for non-type template arguments of enum types.
           // FIXME: Remove this once this is fixed in the AST.
-          unless(hasParent(substNonTypeTemplateParmExpr())),
-          // Avoid matches in template instantiations.
-          unless(isInTemplateInstantiation()))
+          unless(hasParent(substNonTypeTemplateParmExpr())))
           .bind("cast"),
       this);
+
   Finder->addMatcher(
-      cxxFunctionalCastExpr(unless(hasDescendant(cxxConstructExpr())),
-                            unless(hasDescendant(initListExpr())))
+      cxxFunctionalCastExpr(
+          hasDestinationType(hasCanonicalType(anyOf(
+              builtinType(), references(qualType()), pointsTo(qualType())))),
+          unless(
+              hasSourceExpression(anyOf(cxxConstructExpr(), initListExpr()))))
           .bind("cast"),
       this);
 }

clang-tools-extra/clang-tidy/google/AvoidCStyleCastsCheck.h

@@ -31,6 +31,9 @@ class AvoidCStyleCastsCheck : public ClangTidyCheck {
       : ClangTidyCheck(Name, Context) {}
   void registerMatchers(ast_matchers::MatchFinder *Finder) override;
   void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+  std::optional<TraversalKind> getCheckTraversalKind() const override {
+    return TK_IgnoreUnlessSpelledInSource;
+  }
 };
 
 } // namespace clang::tidy::google::readability

clang-tools-extra/docs/ReleaseNotes.rst

@@ -370,6 +370,10 @@ Changes in existing checks
   to ignore unused parameters when they are marked as unused and parameters of
   deleted functions and constructors.
 
+- Improved :doc:`google-readability-casting
+  <clang-tidy/checks/google/readability-casting>` check to ignore constructor
+  calls disguised as functional casts.
+
 - Improved :doc:`llvm-namespace-comment
   <clang-tidy/checks/llvm/namespace-comment>` check to provide fixes for
   ``inline`` namespaces in the same format as :program:`clang-format`.

clang-tools-extra/test/clang-tidy/checkers/google/readability-casting.cpp

@@ -322,17 +322,10 @@ void conversions() {
 }
 
 template <class T>
-T functional_cast_template_used_by_class(float i) {
+T functional_cast_template(float i) {
   return T(i);
 }
 
-template <class T>
-T functional_cast_template_used_by_int(float i) {
-  return T(i);
-  // CHECK-MESSAGES: :[[@LINE-1]]:10: warning: C-style casts are discouraged; use static_cast
-  // CHECK-FIXES: return static_cast<T>(i);
-}
-
 struct S2 {
   S2(float);
 };
@@ -356,8 +349,8 @@ void functional_casts() {
   auto s = S(str);
 
   // Functional casts in template functions
-  functional_cast_template_used_by_class<S2>(x);
-  functional_cast_template_used_by_int<int>(x);
+  functional_cast_template<S2>(x);
+  functional_cast_template<int>(x);
 
   // New expressions are not functional casts
   auto w = new int(x);
@@ -366,4 +359,6 @@ void functional_casts() {
   S2 t = T(x); // OK, constructor call
   S2 u = U(x); // NOK, it's a reinterpret_cast in disguise
   // CHECK-MESSAGES: :[[@LINE-1]]:10: warning: C-style casts are discouraged; use static_cast/const_cast/reinterpret_cast
+
+  throw S2(5.0f);
 }