[clang-tidy] Fix nested namespaces in `readability-static-definition-in-anonymous-namespace` check

[Izaron]

Summary

The check previously inspected only the immediate parent namespace.
static in a named namespace within an unnamed namespace is still redundant.
We will use Decl::isInAnonymousNamespace() method that traverses the
namespaces hierarchy recursively.

[LegalizeAdulthood]

LGTM

[LegalizeAdulthood]

If there is an open github issue on this, please put "Fixes #nnnn" in the commit description before pushing.

[Izaron]

In D118010#3273716, @LegalizeAdulthood wrote:

If there is an open github issue on this, please put "Fixes #nnnn" in the commit description before pushing.

Thanks! I didn't file a github issue. Just searched on github - no one else did it either.

I don't have commit access, so this review could be commited by someone else if that's okay.
If someone is willing to do it, kindly please do it on my behalf =) My name is Evgeny Shulgin, email [e-mail]

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

 #include "clang/Lex/Lexer.h"
 
 using namespace clang::ast_matchers;
 
 namespace clang {
 namespace tidy {
 namespace readability {
 
+AST_MATCHER(NamedDecl, isInAnonymousNamespace) {
+  return Node.isInAnonymousNamespace();
+}
+
 void StaticDefinitionInAnonymousNamespaceCheck::registerMatchers(
     MatchFinder *Finder) {
   Finder->addMatcher(
       namedDecl(anyOf(functionDecl(isDefinition(), isStaticStorageClass()),
                       varDecl(isDefinition(), isStaticStorageClass())),
-                hasParent(namespaceDecl(isAnonymous())))
+                isInAnonymousNamespace())
           .bind("static-def"),
       this);
 }
 
 void StaticDefinitionInAnonymousNamespaceCheck::check(
     const MatchFinder::MatchResult &Result) {
   const auto *Def = Result.Nodes.getNodeAs<NamedDecl>("static-def");
   // Skips all static definitions defined in Macro.

clang-tools-extra/docs/clang-tidy/checks/readability-static-definition-in-anonymous-namespace.rst

 .. title:: clang-tidy - readability-static-definition-in-anonymous-namespace
 
 readability-static-definition-in-anonymous-namespace
 ====================================================
 
 Finds static function and variable definitions in anonymous namespace.
 
 In this case, ``static`` is redundant, because anonymous namespace limits the
 visibility of definitions to a single translation unit.
 
 .. code-block:: c++
 
   namespace {
     static int a = 1; // Warning.
-    static const b = 1; // Warning.
+    static const int b = 1; // Warning.
+    namespace inner {
+      static int c = 1; // Warning.
+    }
   }
 
 The check will apply a fix by removing the redundant ``static`` qualifier.

clang-tools-extra/test/clang-tidy/checkers/readability-static-definition-in-anonymous-namespace.cpp

 // CHECK-MESSAGES: :[[@LINE-1]]:19: warning: 'h' is a static definition in anonymous namespace
 // CHECK-FIXES: {{^}}DEFINE_STATIC int h = 1;
 
 #define DEFINE_STATIC_VAR(x) static int x = 2
 // CHECK-FIXES: {{^}}#define DEFINE_STATIC_VAR(x) static int x = 2
 DEFINE_STATIC_VAR(i);
 // CHECK-FIXES: {{^}}DEFINE_STATIC_VAR(i);
 
+namespace inner {
+int a = 1;
+const int b = 1;
+static int c = 1;
+// CHECK-MESSAGES: :[[@LINE-1]]:12: warning: 'c' is a static definition in anonymous namespace; static is redundant here [readability-static-definition-in-anonymous-namespace]
+// CHECK-FIXES: {{^}}int c = 1;
+namespace deep_inner {
+int a = 1;
+const int b = 1;
+static int c = 1;
+// CHECK-MESSAGES: :[[@LINE-1]]:12: warning: 'c' is a static definition in anonymous namespace; static is redundant here [readability-static-definition-in-anonymous-namespace]
+// CHECK-FIXES: {{^}}int c = 1;
+} // namespace deep_inner
+} // namespace inner
+
 } // namespace
 
 namespace N {
 
 int a = 1;
 const int b = 1;
 static int c = 1;
 static const int d = 1;
 const static int e = 1;
 
 } // namespace N