[clang-tidy] Function-scoped static variables should not trigger google-objc-global-variable-declaration

[benhamilton]

Summary

google-objc-global-variable-declaration currently triggers on
valid code like:

• (void)foo { static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ /* ... */ }); }

The Google Objective-C style guide says:

http://google.github.io/styleguide/objcguide.html#common-variable-names

File scope or global variables (as opposed to constants) declared
outside the scope of a method or function should be rare, and should
have the prefix g.

which is meant to insinuate that static variables inside a method or
function don't need a special name.

Test Plan: make -j12 check-clang-tools

clang-tidy/google/GlobalVariableDeclarationCheck.cpp

 
 namespace clang {
 namespace tidy {
 namespace google {
 namespace objc {
 
 namespace {
 
+AST_MATCHER(VarDecl, isLocalVariable) {
+  return Node.isLocalVarDecl();
+}
+
 FixItHint generateFixItHint(const VarDecl *Decl, bool IsConst) {
   char FC = Decl->getName()[0];
   if (!llvm::isAlpha(FC) || Decl->getName().size() == 1) {
     // No fix available if first character is not alphabetical character, or it
     // is a single-character variable, since it is difficult to determine the 
     // proper fix in this case. Users should create a proper variable name by
     // their own.
     return FixItHint();

 void GlobalVariableDeclarationCheck::registerMatchers(MatchFinder *Finder) {
   // The relevant Style Guide rule only applies to Objective-C.
   if (!getLangOpts().ObjC1 && !getLangOpts().ObjC2) {
     return;
   }
   // need to add two matchers since we need to bind different ids to distinguish
   // constants and variables. Since bind() can only be called on node matchers,
   // we cannot make it in one matcher.
+  //
+  // Note that hasGlobalStorage() matches static variables declared locally
+  // inside a function or method, so we need to exclude those with
+  // isLocalVariable().
   Finder->addMatcher(
       varDecl(hasGlobalStorage(), unless(hasType(isConstQualified())),
-              unless(matchesName("::g[A-Z]")))
+              unless(isLocalVariable()), unless(matchesName("::g[A-Z]")))
           .bind("global_var"),
       this);
   Finder->addMatcher(varDecl(hasGlobalStorage(), hasType(isConstQualified()),
+                             unless(isLocalVariable()),
                              unless(matchesName("::k[A-Z]")))
                          .bind("global_const"),
                      this);
 }
 
 void GlobalVariableDeclarationCheck::check(
     const MatchFinder::MatchResult &Result) {
   if (const auto *Decl = Result.Nodes.getNodeAs<VarDecl>("global_var")) {

test/clang-tidy/google-objc-global-variable-declaration.m

 // CHECK-MESSAGES: :[[@LINE-1]]:24: warning: const global variable '_notAlpha' must have a name which starts with 'k[A-Z]' [google-objc-global-variable-declaration]
 // CHECK-FIXES: static NSString* const _notAlpha = @"NotBeginWithAlpha";
 
 static NSString* const k_Alpha = @"SecondNotAlpha";
 // CHECK-MESSAGES: :[[@LINE-1]]:24: warning: const global variable 'k_Alpha' must have a name which starts with 'k[A-Z]' [google-objc-global-variable-declaration]
 // CHECK-FIXES: static NSString* const k_Alpha = @"SecondNotAlpha";
 
 static NSString* const kGood = @"hello";
-// CHECK-MESSAGES-NOT: :[[@LINE-1]]:24: warning: const global variable 'kGood' must have a name which starts with 'k[A-Z]' [google-objc-global-variable-declaration]
 static NSString* gMyIntGood = 0;
-// CHECK-MESSAGES-NOT: :[[@LINE-1]]:18: warning: non-const global variable 'gMyIntGood' must have a name which starts with 'g[A-Z]' [google-objc-global-variable-declaration]
+
 @implementation Foo
 - (void)f {
     int x = 0;
-// CHECK-MESSAGES-NOT: :[[@LINE-1]]:9: warning: non-const global variable 'gMyIntGood' must have a name which starts with 'g[A-Z]' [google-objc-global-variable-declaration]
+    static int bar;
+    static const int baz = 42;
 }
 @end