[clang-tidy] fix false negatives in readability-redundant-casting when cast function pointer (#170502)

Part of #170476
When check equal of type, we need to ignore ParenType

Author: HerrCai0907

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

@@ -9,6 +9,7 @@
 #include "RedundantCastingCheck.h"
 #include "../utils/FixItHintUtils.h"
 #include "clang/AST/ASTContext.h"
+#include "clang/AST/TypeBase.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
 #include "clang/Lex/Lexer.h"
 
@@ -29,7 +30,7 @@ static bool areTypesEqual(QualType S, QualType D) {
   const QualType PtrD = D->getPointeeType();
 
   if (!PtrS.isNull() && !PtrD.isNull())
-    return areTypesEqual(PtrS, PtrD);
+    return areTypesEqual(PtrS.IgnoreParens(), PtrD.IgnoreParens());
 
   const DeducedType *DT = S->getContainedDeducedType();
   if (DT && DT->isDeduced())

clang-tools-extra/docs/ReleaseNotes.rst

@@ -567,6 +567,10 @@ Changes in existing checks
   <clang-tidy/checks/readability/qualified-auto>` check by adding the option
   `IgnoreAliasing`, that allows not looking at underlying types of type aliases.
 
+- Improved :doc:`readability-redundant-casting
+  <clang-tidy/checks/readability/redundant-casting>` check by fixing false
+  negatives when explicitly cast from function pointer.
+
 - Improved :doc:`readability-uppercase-literal-suffix
   <clang-tidy/checks/readability/uppercase-literal-suffix>` check to recognize
   literal suffixes added in C++23 and C23.

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

@@ -235,3 +235,13 @@ void testRedundantDependentNTTPCasting() {
   // CHECK-MESSAGES: :[[@LINE-4]]:25: note: source type originates from referencing this non-type template parameter
   // CHECK-FIXES: T a = V;
 }
+
+namespace gh170476 {
+int f(void);
+int g1() {
+  int (*fp)() = (int(*)(void))&f;
+  // CHECK-MESSAGES: :[[@LINE-1]]:17: warning: redundant explicit casting to the same type 'int (*)()' as the sub-expression, remove this casting [readability-redundant-casting]
+  // CHECK-FIXES: int (*fp)() = (&f);
+  return fp();
+}
+} // namespace gh170476