[clang-tidy][readability-identifier-naming] Support namespace aliases

Fixes: #109385

Author: keith

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

@@ -1135,6 +1135,9 @@ StyleKind IdentifierNamingCheck::findStyleKind(
   if (isa<TypeAliasDecl>(D) && NamingStyles[SK_TypeAlias])
     return SK_TypeAlias;
 
+  if (isa<NamespaceAliasDecl>(D) && NamingStyles[SK_Namespace])
+    return SK_Namespace;
+
   if (const auto *Decl = dyn_cast<NamespaceDecl>(D)) {
     if (Decl->isAnonymousNamespace())
       return SK_Invalid;

clang-tools-extra/test/clang-tidy/checkers/readability/identifier-naming.cpp

@@ -101,6 +101,10 @@ inline namespace InlineNamespace {
 // CHECK-MESSAGES: :[[@LINE-1]]:18: warning: invalid case style for inline namespace 'InlineNamespace'
 // CHECK-FIXES: {{^}}inline namespace inline_namespace {{{$}}
 
+namespace FOO_ALIAS = FOO_NS;
+// CHECK-MESSAGES: :[[@LINE-1]]:11: warning: invalid case style for namespace 'FOO_ALIAS' [readability-identifier-naming]
+// CHECK-FIXES: {{^}}namespace foo_alias = FOO_NS;{{$}}
+
 SYSTEM_NS::structure g_s1;
 // NO warnings or fixes expected as SYSTEM_NS and structure are declared in a header file