llvm · zwuis · Jul 18, 2025 · Jul 16, 2025
diff --git a/clang-tools-extra/clang-tidy/bugprone/MoveForwardingReferenceCheck.cpp b/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".

diff --git a/clang-tools-extra/clang-tidy/misc/UnusedAliasDeclsCheck.cpp b/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();
     }
   }

diff --git a/clang-tools-extra/clang-tidy/utils/RenamerClangTidyCheck.cpp b/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);
     }
 

diff --git a/clang-tools-extra/clangd/AST.cpp b/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;
                             });
       });
 }

diff --git a/clang-tools-extra/clangd/CodeComplete.cpp b/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:

diff --git a/clang-tools-extra/clangd/DumpAST.cpp b/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 "";
     }

diff --git a/clang-tools-extra/clangd/FindTarget.cpp b/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);

diff --git a/clang-tools-extra/clangd/IncludeFixer.cpp b/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.

diff --git a/clang-tools-extra/clangd/refactor/tweaks/AddUsing.cpp b/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;

diff --git a/clang-tools-extra/include-cleaner/lib/WalkAST.cpp b/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:

diff --git a/clang/include/clang/AST/AbstractBasicReader.h b/clang/include/clang/AST/AbstractBasicReader.h
@@ -269,12 +269,7 @@ class DataStreamBasicReader : public BasicReaderBase<Impl> {
 
       case NestedNameSpecifier::Namespace:
         cur = NestedNameSpecifier::Create(ctx, cur,
-                                          asImpl().readNamespaceDeclRef());
-        continue;
-
-      case NestedNameSpecifier::NamespaceAlias:
-        cur = NestedNameSpecifier::Create(ctx, cur,
-                                     asImpl().readNamespaceAliasDeclRef());
+                                          asImpl().readNamespaceBaseDeclRef());
         continue;
 
       case NestedNameSpecifier::TypeSpec:

diff --git a/clang/include/clang/AST/AbstractBasicWriter.h b/clang/include/clang/AST/AbstractBasicWriter.h
@@ -251,11 +251,7 @@ class DataStreamBasicWriter : public BasicWriterBase<Impl> {
         continue;
 
       case NestedNameSpecifier::Namespace:
-        asImpl().writeNamespaceDeclRef(NNS->getAsNamespace());
-        continue;
-
-      case NestedNameSpecifier::NamespaceAlias:
-        asImpl().writeNamespaceAliasDeclRef(NNS->getAsNamespaceAlias());
+        asImpl().writeNamespaceBaseDeclRef(NNS->getAsNamespace());
         continue;
 
       case NestedNameSpecifier::TypeSpec:

diff --git a/clang/include/clang/AST/Decl.h b/clang/include/clang/AST/Decl.h
@@ -565,8 +565,28 @@ class LabelDecl : public NamedDecl {
   static bool classofKind(Kind K) { return K == Label; }
 };
 
+/// Represents C++ namespaces and their aliases.
+///
+/// FIXME: Move `NamespaceBaseDecl` and `NamespaceDecl` to "DeclCXX.h" or
+/// explain why not moving.
+class NamespaceBaseDecl : public NamedDecl {
+protected:
+  using NamedDecl::NamedDecl;
+
+public:
+  NamespaceDecl *getNamespace();
+  const NamespaceDecl *getNamespace() const {
+    return const_cast<NamespaceBaseDecl *>(this)->getNamespace();
+  }
+
+  static bool classof(const Decl *D) { return classofKind(D->getKind()); }
+  static bool classofKind(Kind K) {
+    return K >= firstNamespaceBase && K <= lastNamespaceBase;
+  }
+};
+
 /// Represent a C++ namespace.
-class NamespaceDecl : public NamedDecl,
+class NamespaceDecl : public NamespaceBaseDecl,
                       public DeclContext,
                       public Redeclarable<NamespaceDecl> {
   /// The starting location of the source range, pointing

diff --git a/clang/include/clang/AST/DeclCXX.h b/clang/include/clang/AST/DeclCXX.h
@@ -3186,7 +3186,7 @@ class UsingDirectiveDecl : public NamedDecl {
 /// \code
 /// namespace Foo = Bar;
 /// \endcode
-class NamespaceAliasDecl : public NamedDecl,
+class NamespaceAliasDecl : public NamespaceBaseDecl,
                            public Redeclarable<NamespaceAliasDecl> {
   friend class ASTDeclReader;
 
@@ -3203,14 +3203,14 @@ class NamespaceAliasDecl : public NamedDecl,
 
   /// The Decl that this alias points to, either a NamespaceDecl or
   /// a NamespaceAliasDecl.
-  NamedDecl *Namespace;
+  NamespaceBaseDecl *Namespace;
 
   NamespaceAliasDecl(ASTContext &C, DeclContext *DC,
                      SourceLocation NamespaceLoc, SourceLocation AliasLoc,
                      IdentifierInfo *Alias, NestedNameSpecifierLoc QualifierLoc,
-                     SourceLocation IdentLoc, NamedDecl *Namespace)
-      : NamedDecl(NamespaceAlias, DC, AliasLoc, Alias), redeclarable_base(C),
-        NamespaceLoc(NamespaceLoc), IdentLoc(IdentLoc),
+                     SourceLocation IdentLoc, NamespaceBaseDecl *Namespace)
+      : NamespaceBaseDecl(NamespaceAlias, DC, AliasLoc, Alias),
+        redeclarable_base(C), NamespaceLoc(NamespaceLoc), IdentLoc(IdentLoc),
         QualifierLoc(QualifierLoc), Namespace(Namespace) {}
 
   void anchor() override;
@@ -3222,13 +3222,11 @@ class NamespaceAliasDecl : public NamedDecl,
   NamespaceAliasDecl *getMostRecentDeclImpl() override;
 
 public:
-  static NamespaceAliasDecl *Create(ASTContext &C, DeclContext *DC,
-                                    SourceLocation NamespaceLoc,
-                                    SourceLocation AliasLoc,
-                                    IdentifierInfo *Alias,
-                                    NestedNameSpecifierLoc QualifierLoc,
-                                    SourceLocation IdentLoc,
-                                    NamedDecl *Namespace);
+  static NamespaceAliasDecl *
+  Create(ASTContext &C, DeclContext *DC, SourceLocation NamespaceLoc,
+         SourceLocation AliasLoc, IdentifierInfo *Alias,
+         NestedNameSpecifierLoc QualifierLoc, SourceLocation IdentLoc,
+         NamespaceBaseDecl *Namespace);
 
   static NamespaceAliasDecl *CreateDeserialized(ASTContext &C, GlobalDeclID ID);
 
@@ -3282,7 +3280,7 @@ class NamespaceAliasDecl : public NamedDecl,
 
   /// Retrieve the namespace that this alias refers to, which
   /// may either be a NamespaceDecl or a NamespaceAliasDecl.
-  NamedDecl *getAliasedNamespace() const { return Namespace; }
+  NamespaceBaseDecl *getAliasedNamespace() const { return Namespace; }
 
   SourceRange getSourceRange() const override LLVM_READONLY {
     return SourceRange(NamespaceLoc, IdentLoc);

diff --git a/clang/include/clang/AST/NestedNameSpecifier.h b/clang/include/clang/AST/NestedNameSpecifier.h
@@ -31,8 +31,7 @@ class ASTContext;
 class CXXRecordDecl;
 class IdentifierInfo;
 class LangOptions;
-class NamespaceAliasDecl;
-class NamespaceDecl;
+class NamespaceBaseDecl;
 struct PrintingPolicy;
 class Type;
 class TypeLoc;
@@ -79,12 +78,9 @@ class NestedNameSpecifier : public llvm::FoldingSetNode {
     /// An identifier, stored as an IdentifierInfo*.
     Identifier,
 
-    /// A namespace, stored as a NamespaceDecl*.
+    /// A namespace-like entity, stored as a NamespaceBaseDecl*.
     Namespace,
 
-    /// A namespace alias, stored as a NamespaceAliasDecl*.
-    NamespaceAlias,
-
     /// A type, stored as a Type*.
     TypeSpec,
 
@@ -121,15 +117,10 @@ class NestedNameSpecifier : public llvm::FoldingSetNode {
                                      NestedNameSpecifier *Prefix,
                                      const IdentifierInfo *II);
 
-  /// Builds a nested name specifier that names a namespace.
-  static NestedNameSpecifier *Create(const ASTContext &Context,
-                                     NestedNameSpecifier *Prefix,
-                                     const NamespaceDecl *NS);
-
-  /// Builds a nested name specifier that names a namespace alias.
+  /// Builds a nested name specifier that names a namespace or namespace alias.
   static NestedNameSpecifier *Create(const ASTContext &Context,
                                      NestedNameSpecifier *Prefix,
-                                     const NamespaceAliasDecl *Alias);
+                                     const NamespaceBaseDecl *NS);
 
   /// Builds a nested name specifier that names a type.
   static NestedNameSpecifier *
@@ -174,13 +165,9 @@ class NestedNameSpecifier : public llvm::FoldingSetNode {
     return nullptr;
   }
 
-  /// Retrieve the namespace stored in this nested name
+  /// Retrieve the namespace or namespace alias stored in this nested name
   /// specifier.
-  NamespaceDecl *getAsNamespace() const;
-
-  /// Retrieve the namespace alias stored in this nested name
-  /// specifier.
-  NamespaceAliasDecl *getAsNamespaceAlias() const;
+  NamespaceBaseDecl *getAsNamespace() const;
 
   /// Retrieve the record declaration stored in this nested name
   /// specifier.
@@ -425,29 +412,15 @@ class NestedNameSpecifierLocBuilder {
   /// \param Context The AST context in which this nested-name-specifier
   /// resides.
   ///
-  /// \param Namespace The namespace.
+  /// \param Namespace The namespace or namespace alias.
   ///
-  /// \param NamespaceLoc The location of the namespace name.
+  /// \param NamespaceLoc The location of the namespace name or the namespace
+  //  alias.
   ///
   /// \param ColonColonLoc The location of the trailing '::'.
-  void Extend(ASTContext &Context, NamespaceDecl *Namespace,
+  void Extend(ASTContext &Context, NamespaceBaseDecl *Namespace,
               SourceLocation NamespaceLoc, SourceLocation ColonColonLoc);
 
-  /// Extend the current nested-name-specifier by another
-  /// nested-name-specifier component of the form 'namespace-alias::'.
-  ///
-  /// \param Context The AST context in which this nested-name-specifier
-  /// resides.
-  ///
-  /// \param Alias The namespace alias.
-  ///
-  /// \param AliasLoc The location of the namespace alias
-  /// name.
-  ///
-  /// \param ColonColonLoc The location of the trailing '::'.
-  void Extend(ASTContext &Context, NamespaceAliasDecl *Alias,
-              SourceLocation AliasLoc, SourceLocation ColonColonLoc);
-
   /// Turn this (empty) nested-name-specifier into the global
   /// nested-name-specifier '::'.
   void MakeGlobal(ASTContext &Context, SourceLocation ColonColonLoc);

diff --git a/clang/include/clang/AST/PropertiesBase.td b/clang/include/clang/AST/PropertiesBase.td
@@ -91,6 +91,7 @@ def DeclRef : RefPropertyType<"Decl"> { let ConstWhenWriting = 1; }
     SubclassPropertyType<"FunctionDecl", DeclRef>;
   def NamedDeclRef :
     SubclassPropertyType<"NamedDecl", DeclRef>;
+  def NamespaceBaseDeclRef : SubclassPropertyType<"NamespaceBaseDecl", DeclRef>;
   def NamespaceDeclRef :
     SubclassPropertyType<"NamespaceDecl", DeclRef>;
   def NamespaceAliasDeclRef :

diff --git a/clang/include/clang/AST/RecursiveASTVisitor.h b/clang/include/clang/AST/RecursiveASTVisitor.h
@@ -789,7 +789,6 @@ bool RecursiveASTVisitor<Derived>::TraverseNestedNameSpecifier(
   switch (NNS->getKind()) {
   case NestedNameSpecifier::Identifier:
   case NestedNameSpecifier::Namespace:
-  case NestedNameSpecifier::NamespaceAlias:
   case NestedNameSpecifier::Global:
   case NestedNameSpecifier::Super:
     return true;
@@ -813,7 +812,6 @@ bool RecursiveASTVisitor<Derived>::TraverseNestedNameSpecifierLoc(
   switch (NNS.getNestedNameSpecifier()->getKind()) {
   case NestedNameSpecifier::Identifier:
   case NestedNameSpecifier::Namespace:
-  case NestedNameSpecifier::NamespaceAlias:
   case NestedNameSpecifier::Global:
   case NestedNameSpecifier::Super:
     return true;

diff --git a/clang/include/clang/ASTMatchers/ASTMatchers.h b/clang/include/clang/ASTMatchers/ASTMatchers.h
@@ -7894,9 +7894,9 @@ AST_MATCHER_P_OVERLOAD(NestedNameSpecifierLoc, hasPrefix,
 ///   matches "ns::"
 AST_MATCHER_P(NestedNameSpecifier, specifiesNamespace,
               internal::Matcher<NamespaceDecl>, InnerMatcher) {
-  if (!Node.getAsNamespace())
-    return false;
-  return InnerMatcher.matches(*Node.getAsNamespace(), Finder, Builder);
+  if (auto *NS = dyn_cast_if_present<NamespaceDecl>(Node.getAsNamespace()))
+    return InnerMatcher.matches(*NS, Finder, Builder);
+  return false;
 }
 
 /// Matches attributes.