[Clang][AST][NFC] Introduce NamespaceBaseDecl (#149123)

Add `NamespaceBaseDecl` as common base class of `NamespaceDecl` and
`NamespaceAliasDecl`. This simplifies `NestedNameSpecifier` a bit.

Co-authored-by: Matheus Izvekov <[email protected]>

Author: zwuis

clang-tools-extra/clang-tidy/bugprone/MoveForwardingReferenceCheck.cpp

@@ -45,7 +45,7 @@ static void replaceMoveWithForward(const UnresolvedLookupExpr *Callee,
       // We still conservatively put a "std::" in front of the forward because
       // we don't know whether the code also had a "using std::forward;".
       Diag << FixItHint::CreateReplacement(CallRange, "std::" + ForwardName);
-    } else if (const NamespaceDecl *Namespace = NNS->getAsNamespace()) {
+    } else if (const NamespaceBaseDecl *Namespace = NNS->getAsNamespace()) {
       if (Namespace->getName() == "std") {
         if (!NNS->getPrefix()) {
           // Called as "std::move".

clang-tools-extra/clang-tidy/misc/UnusedAliasDeclsCheck.cpp

@@ -36,7 +36,8 @@ void UnusedAliasDeclsCheck::check(const MatchFinder::MatchResult &Result) {
 
   if (const auto *NestedName =
           Result.Nodes.getNodeAs<NestedNameSpecifier>("nns")) {
-    if (const auto *AliasDecl = NestedName->getAsNamespaceAlias()) {
+    if (const auto *AliasDecl = dyn_cast_if_present<NamespaceAliasDecl>(
+            NestedName->getAsNamespace())) {
       FoundDecls[AliasDecl] = CharSourceRange();
     }
   }

clang-tools-extra/clang-tidy/utils/RenamerClangTidyCheck.cpp

@@ -282,7 +282,8 @@ class RenamerClangTidyVisitor
 
   bool TraverseNestedNameSpecifierLoc(NestedNameSpecifierLoc Loc) {
     if (const NestedNameSpecifier *Spec = Loc.getNestedNameSpecifier()) {
-      if (const NamespaceDecl *Decl = Spec->getAsNamespace())
+      if (const auto *Decl =
+              dyn_cast_if_present<NamespaceDecl>(Spec->getAsNamespace()))
         Check->addUsage(Decl, Loc.getLocalSourceRange(), SM);
     }
 

clang-tools-extra/clangd/AST.cpp

@@ -666,12 +666,14 @@ std::string getQualification(ASTContext &Context,
   return getQualification(
       Context, DestContext, ND->getDeclContext(),
       [&](NestedNameSpecifier *NNS) {
-        if (NNS->getKind() != NestedNameSpecifier::Namespace)
+        const NamespaceDecl *NS =
+            dyn_cast_if_present<NamespaceDecl>(NNS->getAsNamespace());
+        if (!NS)
           return false;
-        const auto *CanonNSD = NNS->getAsNamespace()->getCanonicalDecl();
+        NS = NS->getCanonicalDecl();
         return llvm::any_of(VisibleNamespaceDecls,
-                            [CanonNSD](const NamespaceDecl *NSD) {
-                              return NSD->getCanonicalDecl() == CanonNSD;
+                            [NS](const NamespaceDecl *NSD) {
+                              return NSD->getCanonicalDecl() == NS;
                             });
       });
 }

clang-tools-extra/clangd/CodeComplete.cpp

@@ -1470,7 +1470,6 @@ bool allowIndex(CodeCompletionContext &CC) {
   switch (NameSpec->getKind()) {
   case NestedNameSpecifier::Global:
   case NestedNameSpecifier::Namespace:
-  case NestedNameSpecifier::NamespaceAlias:
     return true;
   case NestedNameSpecifier::Super:
   case NestedNameSpecifier::TypeSpec:

clang-tools-extra/clangd/DumpAST.cpp

@@ -158,7 +158,6 @@ class DumpVisitor : public RecursiveASTVisitor<DumpVisitor> {
       NNS_KIND(TypeSpec);
       NNS_KIND(Global);
       NNS_KIND(Super);
-      NNS_KIND(NamespaceAlias);
 #undef NNS_KIND
     }
     llvm_unreachable("Unhandled SpecifierKind enum");
@@ -281,8 +280,6 @@ class DumpVisitor : public RecursiveASTVisitor<DumpVisitor> {
       return NNS.getAsIdentifier()->getName().str() + "::";
     case NestedNameSpecifier::Namespace:
       return NNS.getAsNamespace()->getNameAsString() + "::";
-    case NestedNameSpecifier::NamespaceAlias:
-      return NNS.getAsNamespaceAlias()->getNameAsString() + "::";
     default:
       return "";
     }

clang-tools-extra/clangd/FindTarget.cpp

@@ -491,9 +491,6 @@ struct TargetFinder {
     case NestedNameSpecifier::Namespace:
       add(NNS->getAsNamespace(), Flags);
       return;
-    case NestedNameSpecifier::NamespaceAlias:
-      add(NNS->getAsNamespaceAlias(), Flags);
-      return;
     case NestedNameSpecifier::Identifier:
       if (Resolver) {
         add(Resolver->resolveNestedNameSpecifierToType(NNS), Flags);

clang-tools-extra/clangd/IncludeFixer.cpp

@@ -403,25 +403,27 @@ std::optional<CheapUnresolvedName> extractUnresolvedNameCheaply(
     if (auto *Nested = SS->getScopeRep()) {
       if (Nested->getKind() == NestedNameSpecifier::Global) {
         Result.ResolvedScope = "";
-      } else if (const auto *NS = Nested->getAsNamespace()) {
-        std::string SpecifiedNS = printNamespaceScope(*NS);
-        std::optional<std::string> Spelling = getSpelledSpecifier(*SS, SM);
-
-        // Check the specifier spelled in the source.
-        // If the resolved scope doesn't end with the spelled scope, the
-        // resolved scope may come from a sema typo correction. For example,
-        // sema assumes that "clangd::" is a typo of "clang::" and uses
-        // "clang::" as the specified scope in:
-        //     namespace clang { clangd::X; }
-        // In this case, we use the "typo" specifier as extra scope instead
-        // of using the scope assumed by sema.
-        if (!Spelling || llvm::StringRef(SpecifiedNS).ends_with(*Spelling)) {
-          Result.ResolvedScope = std::move(SpecifiedNS);
+      } else if (const NamespaceBaseDecl *NSB = Nested->getAsNamespace()) {
+        if (const auto *NS = dyn_cast<NamespaceDecl>(NSB)) {
+          std::string SpecifiedNS = printNamespaceScope(*NS);
+          std::optional<std::string> Spelling = getSpelledSpecifier(*SS, SM);
+
+          // Check the specifier spelled in the source.
+          // If the resolved scope doesn't end with the spelled scope, the
+          // resolved scope may come from a sema typo correction. For example,
+          // sema assumes that "clangd::" is a typo of "clang::" and uses
+          // "clang::" as the specified scope in:
+          //     namespace clang { clangd::X; }
+          // In this case, we use the "typo" specifier as extra scope instead
+          // of using the scope assumed by sema.
+          if (!Spelling || llvm::StringRef(SpecifiedNS).ends_with(*Spelling)) {
+            Result.ResolvedScope = std::move(SpecifiedNS);
+          } else {
+            Result.UnresolvedScope = std::move(*Spelling);
+          }
         } else {
-          Result.UnresolvedScope = std::move(*Spelling);
+          Result.ResolvedScope = printNamespaceScope(*cast<NamespaceAliasDecl>(NSB)->getNamespace());
         }
-      } else if (const auto *ANS = Nested->getAsNamespaceAlias()) {
-        Result.ResolvedScope = printNamespaceScope(*ANS->getNamespace());
       } else {
         // We don't fix symbols in scopes that are not top-level e.g. class
         // members, as we don't collect includes for them.

clang-tools-extra/clangd/refactor/tweaks/AddUsing.cpp

@@ -173,7 +173,8 @@ findInsertionPoint(const Tweak::Selection &Inputs,
     if (SM.isBeforeInTranslationUnit(Inputs.Cursor, U->getUsingLoc()))
       // "Usings" is sorted, so we're done.
       break;
-    if (const auto *Namespace = U->getQualifier()->getAsNamespace()) {
+    if (const auto *Namespace = dyn_cast_if_present<NamespaceDecl>(
+            U->getQualifier()->getAsNamespace())) {
       if (Namespace->getCanonicalDecl() ==
               QualifierToRemove.getNestedNameSpecifier()
                   ->getAsNamespace()
@@ -232,7 +233,10 @@ findInsertionPoint(const Tweak::Selection &Inputs,
 
 bool isNamespaceForbidden(const Tweak::Selection &Inputs,
                           const NestedNameSpecifier &Namespace) {
-  std::string NamespaceStr = printNamespaceScope(*Namespace.getAsNamespace());
+  const auto *NS = dyn_cast<NamespaceDecl>(Namespace.getAsNamespace());
+  if (!NS)
+    return true;
+  std::string NamespaceStr = printNamespaceScope(*NS);
 
   for (StringRef Banned : Config::current().Style.FullyQualifiedNamespaces) {
     StringRef PrefixMatch = NamespaceStr;

clang-tools-extra/include-cleaner/lib/WalkAST.cpp

@@ -140,7 +140,6 @@ class ASTWalker : public RecursiveASTVisitor<ASTWalker> {
       return true;
     switch (Qual->getKind()) {
     case NestedNameSpecifier::Namespace:
-    case NestedNameSpecifier::NamespaceAlias:
     case NestedNameSpecifier::Global:
       return true;
     case NestedNameSpecifier::TypeSpec: