[clang-tidy] fix a false positive of `cppcoreguidelines-avoid-non-const-global-variables`

[v1nh1shungry]

Summary

Currently this checker will report the non-const static
private/protected member of a class/struct.

Fixes https://github.com/llvm/llvm-project/issues/57919

[njames93]

I'm not convinced this is the correct fix.
The guildline states that tools should flag all variables declared at global or namespace scope.
Therefore we shouldn't be flagging any class static members, no matter if they are public, private or protected.

clang-tools-extra/clang-tidy/cppcoreguidelines/AvoidNonConstGlobalVariablesCheck.cpp

 AST_MATCHER(VarDecl, isLocalVarDecl) { return Node.isLocalVarDecl(); }
 } // namespace
 
 void AvoidNonConstGlobalVariablesCheck::registerMatchers(MatchFinder *Finder) {
   auto GlobalVariable = varDecl(
       hasGlobalStorage(),
       unless(anyOf(
           isLocalVarDecl(), isConstexpr(), hasType(isConstQualified()),
+          isPrivate(), isProtected(),
           hasType(referenceType())))); // References can't be changed, only the
                                        // data they reference can be changed.
 
   auto GlobalReferenceToNonConst =
       varDecl(hasGlobalStorage(), hasType(referenceType()),
               unless(hasType(references(qualType(isConstQualified())))));
 
   auto GlobalPointerToNonConst =

clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/avoid-non-const-global-variables.cpp

 typedef int (*const functionConstPointer)();
 functionPointer fp2 = &dummyFunction;
 // CHECK-MESSAGES: :[[@LINE-1]]:17: warning: variable 'fp2' is non-const and globally accessible, consider making it const [cppcoreguidelines-avoid-non-const-global-variables]
 
 // CHECKING FOR NON-CONST GLOBAL TEMPLATE VARIABLE ////////////////////////////
 template <class T>
 constexpr T templateVariable = T(0L);
 
+// CHECKING FOR NON-CONST STATIC PRIVATE/PROTECTED CLASS MEMBERS //////////////
+class Foo {
+  static int nonConstStaticPrivateMember;
+protected:
+  static int nonConstStaticProtectedMember;
+};
+
+struct Bar {
+private:
+  static int nonConstStaticPrivateMember;
+protected:
+  static int nonConstStaticProtectedMember;
+};
+
 // CHECKING AGAINST FALSE POSITIVES INSIDE FUNCTION SCOPE /////////////////////
 int main() {
   for (int i = 0; i < 3; ++i) {
     static int staticNonConstLoopVariable = 42;
     int nonConstLoopVariable = 42;
     nonConstInt = nonConstLoopVariable + i + staticNonConstLoopVariable;
   }
 }