[clang] Add [is|set]Nested methods to NamespaceDecl

[njames93]

Summary

Adds support for NamespaceDecl to inform if its part of a nested namespace.
This flag only corresponds to the inner namespaces in a nested namespace declaration.
In this example:
namespace <X>::<Y>::<Z> {}
Only <Y> and <Z> will be classified as nested.

This flag isn't meant for assisting in building the AST, more for static analysis and refactorings.

[Mordante]

Just a few minor nits. I'll leave the approving to the other reviewers.

clang/lib/AST/TextNodeDumper.cpp

1935

Can you also modify JSONNodeDumper::VisitNamespaceDecl ?

clang/lib/Sema/SemaDeclCXX.cpp

11516

Please change false to /*Nested=*/false.

[shafik]

clang/lib/AST/ASTContext.cpp

8766–8770

As noted elsewhere instead of just false please use /*Nested*/ false

Also a little below.

[njames93]

Added JsonNodeDumper and argument comments.

[Mordante]

In D90568#2370079, @njames93 wrote:

Added JsonNodeDumper and argument comments.

Thanks, I've no further comments.

[njames93]

Ping?

[njames93]

Ping?

[njames93]

Rebased
Changed logic so inner namespaces are marked as nester(which makes much more sense imo)

[njames93]

Fix clang-format

[aaron.ballman]

Generally LGTM, though I found a few minor things.

clang/include/clang/AST/Decl.h

546

I'm not really loving the F_ prefixes -- the enumerators are already privately scoped to NamespaceDecl, is that not sufficient protection?

clang/lib/AST/DeclCXX.cpp

2887

I love it and hate it in equal measures; I think multiplying a bool and an enumerator together is just a bit too clever. How about:

unsigned Flags = 0;
if (Inline) Flags |= F_Inline;
if (Nested) Flags |= F_Nested;
AnonOrFirstNamespaceAndFlags(nullptr, Flags);

It's longer, but I think it's also more clear.

clang/lib/AST/ItaniumMangle.cpp

602–607

Not your problem, but I'm curious if you agree: we should probably have a helper method for getting the std namespace (and creating it if necessary) so we don't do this dance in at least three different places.

[njames93]

Clean up initializer.

[shafik]

clang/lib/AST/ASTContext.cpp

8767–8770

Overriding my old comment from a while ago,

8957–8959

clang/lib/AST/ItaniumMangle.cpp

605–607

clang/lib/Sema/HLSLExternalSemaSource.cpp

390

[njames93]

Fix comments.

clang/include/clang/AST/Decl.h

546

I think just having it named as Inline and Nested is going to confuse things even more, BlockDecl seems to use flag_is<FLAG> for its packing, and I think that is even worse. WDYT

[njames93]

clang/test/AST/ast-dump-decl.cpp

823

This is confusing me, I'm not sure exactly why this file appears to have been complete changed when it doesn't appear to, CL/LF maybe?

[aaron.ballman]

clang/include/clang/AST/Decl.h

546

Eh, I don't feel super strongly, but if you want to force there to be a qualified name, then I'd hoist it out of NamespaceDecl and make a scoped enum so you can write Namespace::Inline or Namespace::Nested.

clang/test/AST/ast-dump-decl.cpp

823

Yeah this looks like a line ending change slipped in because Phab is showing green/red on lines with no visible modifications. FWIW, my local copy seems to be using UNIX line endings and not Windows line endings.

[njames93]

Hopefully fixed line endings

[thakis]

This breaks the build: http://45.33.8.238/linux/92294/step_4.txt

Please take a look and revert for now if it takes a while to fix.

[njames93]

In D90568#3949134, @thakis wrote:

This breaks the build: http://45.33.8.238/linux/92294/step_4.txt

Please take a look and revert for now if it takes a while to fix.

Apologies it took 2 times, It should all be good now, lmk if there's any other issues.

[thakis]

My bots look happy at least. Thanks for the quick fix!

clang/include/clang/AST/Decl.h

public:
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == Label; }
 };
 
 /// Represent a C++ namespace.
 class NamespaceDecl : public NamedDecl, public DeclContext,
                       public Redeclarable<NamespaceDecl>
 {
+
+  enum Flags : unsigned { F_Inline = 1 << 0, F_Nested = 1 << 1 };
+
   /// The starting location of the source range, pointing
   /// to either the namespace or the inline keyword.
   SourceLocation LocStart;
 
   /// The ending location of the source range.
   SourceLocation RBraceLoc;
 
   /// A pointer to either the anonymous namespace that lives just inside
   /// this namespace or to the first namespace in the chain (the latter case
   /// only when this is not the first in the chain), along with a
   /// boolean value indicating whether this is an inline namespace.
-  llvm::PointerIntPair<NamespaceDecl *, 1, bool> AnonOrFirstNamespaceAndInline;
+  llvm::PointerIntPair<NamespaceDecl *, 2, unsigned>
+      AnonOrFirstNamespaceAndFlags;
 
   NamespaceDecl(ASTContext &C, DeclContext *DC, bool Inline,
                 SourceLocation StartLoc, SourceLocation IdLoc,
-                IdentifierInfo *Id, NamespaceDecl *PrevDecl);
+                IdentifierInfo *Id, NamespaceDecl *PrevDecl, bool Nested);
 
   using redeclarable_base = Redeclarable<NamespaceDecl>;
 
   NamespaceDecl *getNextRedeclarationImpl() override;
   NamespaceDecl *getPreviousDeclImpl() override;
   NamespaceDecl *getMostRecentDeclImpl() override;
 
 public:
   friend class ASTDeclReader;
   friend class ASTDeclWriter;
 
-  static NamespaceDecl *Create(ASTContext &C, DeclContext *DC,
-                               bool Inline, SourceLocation StartLoc,
-                               SourceLocation IdLoc, IdentifierInfo *Id,
-                               NamespaceDecl *PrevDecl);
+  static NamespaceDecl *Create(ASTContext &C, DeclContext *DC, bool Inline,
+                               SourceLocation StartLoc, SourceLocation IdLoc,
+                               IdentifierInfo *Id, NamespaceDecl *PrevDecl,
+                               bool Nested);
 
   static NamespaceDecl *CreateDeserialized(ASTContext &C, unsigned ID);
 
   using redecl_range = redeclarable_base::redecl_range;
   using redecl_iterator = redeclarable_base::redecl_iterator;
 
   using redeclarable_base::redecls_begin;
   using redeclarable_base::redecls_end;
public:
   /// \endcode
   /// q.v. C++ [namespace.unnamed]
   bool isAnonymousNamespace() const {
     return !getIdentifier();
   }
 
   /// Returns true if this is an inline namespace declaration.
   bool isInline() const {
-    return AnonOrFirstNamespaceAndInline.getInt();
+    return AnonOrFirstNamespaceAndFlags.getInt() & F_Inline;
   }
 
   /// Set whether this is an inline namespace declaration.
   void setInline(bool Inline) {
-    AnonOrFirstNamespaceAndInline.setInt(Inline);
+    unsigned F = AnonOrFirstNamespaceAndFlags.getInt();
+    if (Inline)
+      AnonOrFirstNamespaceAndFlags.setInt(F | F_Inline);
+    else
+      AnonOrFirstNamespaceAndFlags.setInt(F & ~F_Inline);
+  }
+
+  /// Returns true if this is a nested namespace declaration.
+  /// \code
+  /// namespace outer::nested { }
+  /// \endcode
+  bool isNested() const {
+    return AnonOrFirstNamespaceAndFlags.getInt() & F_Nested;
+  }
+
+  /// Set whether this is a nested namespace declaration.
+  void setNested(bool Nested) {
+    unsigned F = AnonOrFirstNamespaceAndFlags.getInt();
+    if (Nested)
+      AnonOrFirstNamespaceAndFlags.setInt(F | F_Nested);
+    else
+      AnonOrFirstNamespaceAndFlags.setInt(F & ~F_Nested);
   }
 
   /// Returns true if the inline qualifier for \c Name is redundant.
   bool isRedundantInlineQualifierFor(DeclarationName Name) const {
     if (!isInline())
       return false;
     auto X = lookup(Name);
     // We should not perform a lookup within a transparent context, so find a
public:
   /// Return true if this declaration is an original (first) declaration
   /// of the namespace. This is false for non-original (subsequent) namespace
   /// declarations and anonymous namespaces.
   bool isOriginalNamespace() const;
 
   /// Retrieve the anonymous namespace nested inside this namespace,
   /// if any.
   NamespaceDecl *getAnonymousNamespace() const {
-    return getOriginalNamespace()->AnonOrFirstNamespaceAndInline.getPointer();
+    return getOriginalNamespace()->AnonOrFirstNamespaceAndFlags.getPointer();
   }
 
   void setAnonymousNamespace(NamespaceDecl *D) {
-    getOriginalNamespace()->AnonOrFirstNamespaceAndInline.setPointer(D);
+    getOriginalNamespace()->AnonOrFirstNamespaceAndFlags.setPointer(D);
   }
 
   /// Retrieves the canonical declaration of this namespace.
   NamespaceDecl *getCanonicalDecl() override {
     return getOriginalNamespace();
   }
   const NamespaceDecl *getCanonicalDecl() const {
     return getOriginalNamespace();

clang/include/clang/Sema/Sema.h

public:
   //===---------------------------- C++ Features --------------------------===//
 
   // Act on C++ namespaces
   Decl *ActOnStartNamespaceDef(Scope *S, SourceLocation InlineLoc,
                                SourceLocation NamespaceLoc,
                                SourceLocation IdentLoc, IdentifierInfo *Ident,
                                SourceLocation LBrace,
                                const ParsedAttributesView &AttrList,
-                               UsingDirectiveDecl *&UsingDecl);
+                               UsingDirectiveDecl *&UsingDecl, bool IsNested);
   void ActOnFinishNamespaceDef(Decl *Dcl, SourceLocation RBrace);
 
   NamespaceDecl *getStdNamespace() const;
   NamespaceDecl *getOrCreateStdNamespace();
 
   NamespaceDecl *lookupStdExperimentalNamespace();
   NamespaceDecl *getCachedCoroNamespace() { return CoroTraitsNamespaceCache; }
 

clang/lib/AST/ASTContext.cpp

 }
 
 static TypedefDecl *
 CreateAArch64ABIBuiltinVaListDecl(const ASTContext *Context) {
   // struct __va_list
   RecordDecl *VaListTagDecl = Context->buildImplicitRecord("__va_list");
   if (Context->getLangOpts().CPlusPlus) {
     // namespace std { struct __va_list {
     auto *NS = NamespaceDecl::Create(
         const_cast<ASTContext &>(*Context), Context->getTranslationUnitDecl(),
-        /*Inline*/ false, SourceLocation(), SourceLocation(),
+        /*Inline=*/false, SourceLocation(), SourceLocation(),
         &Context->Idents.get("std"),
-        /*PrevDecl*/ nullptr);
+        /*PrevDecl=*/nullptr, /*Nested=*/false);
     NS->setImplicit();
     VaListTagDecl->setDeclContext(NS);
   }
 
   VaListTagDecl->startDefinition();
 
   const size_t NumFields = 5;
   QualType FieldTypes[NumFields];

 CreateAAPCSABIBuiltinVaListDecl(const ASTContext *Context) {
   // struct __va_list
   RecordDecl *VaListDecl = Context->buildImplicitRecord("__va_list");
   if (Context->getLangOpts().CPlusPlus) {
     // namespace std { struct __va_list {
     NamespaceDecl *NS;
     NS = NamespaceDecl::Create(const_cast<ASTContext &>(*Context),
                                Context->getTranslationUnitDecl(),
-                               /*Inline*/false, SourceLocation(),
+                               /*Inline=*/false, SourceLocation(),
                                SourceLocation(), &Context->Idents.get("std"),
-                               /*PrevDecl*/ nullptr);
+                               /*PrevDecl=*/nullptr, /*Nested=*/false);
     NS->setImplicit();
     VaListDecl->setDeclContext(NS);
   }
 
   VaListDecl->startDefinition();
 
   // void * __ap;
   FieldDecl *Field = FieldDecl::Create(const_cast<ASTContext &>(*Context),

clang/lib/AST/ASTImporter.cpp

if (!BeginLocOrErr)
     return BeginLocOrErr.takeError();
   ExpectedSLoc RBraceLocOrErr = import(D->getRBraceLoc());
   if (!RBraceLocOrErr)
     return RBraceLocOrErr.takeError();
 
   // Create the "to" namespace, if needed.
   NamespaceDecl *ToNamespace = MergeWithNamespace;
   if (!ToNamespace) {
-    if (GetImportedOrCreateDecl(
-            ToNamespace, D, Importer.getToContext(), DC, D->isInline(),
-            *BeginLocOrErr, Loc, Name.getAsIdentifierInfo(),
-            /*PrevDecl=*/nullptr))
+    if (GetImportedOrCreateDecl(ToNamespace, D, Importer.getToContext(), DC,
+                                D->isInline(), *BeginLocOrErr, Loc,
+                                Name.getAsIdentifierInfo(),
+                                /*PrevDecl=*/nullptr, D->isNested()))
       return ToNamespace;
     ToNamespace->setRBraceLoc(*RBraceLocOrErr);
     ToNamespace->setLexicalDeclContext(LexicalDC);
     LexicalDC->addDeclInternal(ToNamespace);
 
     // If this is an anonymous namespace, register it as the anonymous
     // namespace within its context.
     if (!Name) {

clang/lib/AST/DeclCXX.cpp

 NamespaceDecl *UsingDirectiveDecl::getNominatedNamespace() {
   if (auto *NA = dyn_cast_or_null<NamespaceAliasDecl>(NominatedNamespace))
     return NA->getNamespace();
   return cast_or_null<NamespaceDecl>(NominatedNamespace);
 }
 
 NamespaceDecl::NamespaceDecl(ASTContext &C, DeclContext *DC, bool Inline,
                              SourceLocation StartLoc, SourceLocation IdLoc,
-                             IdentifierInfo *Id, NamespaceDecl *PrevDecl)
+                             IdentifierInfo *Id, NamespaceDecl *PrevDecl,
+                             bool Nested)
     : NamedDecl(Namespace, DC, IdLoc, Id), DeclContext(Namespace),
-      redeclarable_base(C), LocStart(StartLoc),
-      AnonOrFirstNamespaceAndInline(nullptr, Inline) {
+      redeclarable_base(C), LocStart(StartLoc) {
+  unsigned Flags = 0;
+  if (Inline)
+    Flags |= F_Inline;
+  if (Nested)
+    Flags |= F_Nested;
+  AnonOrFirstNamespaceAndFlags = {nullptr, Flags};
   setPreviousDecl(PrevDecl);
 
   if (PrevDecl)
-    AnonOrFirstNamespaceAndInline.setPointer(PrevDecl->getOriginalNamespace());
+    AnonOrFirstNamespaceAndFlags.setPointer(PrevDecl->getOriginalNamespace());
 }
 
 NamespaceDecl *NamespaceDecl::Create(ASTContext &C, DeclContext *DC,
                                      bool Inline, SourceLocation StartLoc,
                                      SourceLocation IdLoc, IdentifierInfo *Id,
-                                     NamespaceDecl *PrevDecl) {
-  return new (C, DC) NamespaceDecl(C, DC, Inline, StartLoc, IdLoc, Id,
-                                   PrevDecl);
+                                     NamespaceDecl *PrevDecl, bool Nested) {
+  return new (C, DC)
+      NamespaceDecl(C, DC, Inline, StartLoc, IdLoc, Id, PrevDecl, Nested);
 }
 
 NamespaceDecl *NamespaceDecl::CreateDeserialized(ASTContext &C, unsigned ID) {
   return new (C, ID) NamespaceDecl(C, nullptr, false, SourceLocation(),
-                                   SourceLocation(), nullptr, nullptr);
+                                   SourceLocation(), nullptr, nullptr, false);
 }
 
 NamespaceDecl *NamespaceDecl::getOriginalNamespace() {
   if (isFirstDecl())
     return this;
 
-  return AnonOrFirstNamespaceAndInline.getPointer();
+  return AnonOrFirstNamespaceAndFlags.getPointer();
 }
 
 const NamespaceDecl *NamespaceDecl::getOriginalNamespace() const {
   if (isFirstDecl())
     return this;
 
-  return AnonOrFirstNamespaceAndInline.getPointer();
+  return AnonOrFirstNamespaceAndFlags.getPointer();
 }
 
 bool NamespaceDecl::isOriginalNamespace() const { return isFirstDecl(); }
 
 NamespaceDecl *NamespaceDecl::getNextRedeclarationImpl() {
   return getNextRedeclaration();
 }
 

clang/lib/AST/ItaniumMangle.cpp

#include "clang/AST/TypeNodes.inc"
   AbiTagList makeFunctionReturnTypeTags(const FunctionDecl *FD);
   // Returns sorted unique list of ABI tags.
   AbiTagList makeVariableTypeTags(const VarDecl *VD);
 };
 
 }
 
 NamespaceDecl *ItaniumMangleContextImpl::getStdNamespace() {
   if (!StdNamespace) {
     StdNamespace = NamespaceDecl::Create(
         getASTContext(), getASTContext().getTranslationUnitDecl(),
-        /*Inline*/ false, SourceLocation(), SourceLocation(),
+        /*Inline=*/false, SourceLocation(), SourceLocation(),
         &getASTContext().Idents.get("std"),
-        /*PrevDecl*/ nullptr);
+        /*PrevDecl=*/nullptr, /*Nested=*/false);
     StdNamespace->setImplicit();
   }
   return StdNamespace;
 }
 
 /// Retrieve the declaration context that should be used when mangling the given
 /// declaration.
 const DeclContext *

clang/lib/AST/JSONNodeDumper.cpp

 void JSONNodeDumper::VisitTypeAliasDecl(const TypeAliasDecl *TAD) {
   VisitNamedDecl(TAD);
   JOS.attribute("type", createQualType(TAD->getUnderlyingType()));
 }
 
 void JSONNodeDumper::VisitNamespaceDecl(const NamespaceDecl *ND) {
   VisitNamedDecl(ND);
   attributeOnlyIfTrue("isInline", ND->isInline());
+  attributeOnlyIfTrue("isNested", ND->isNested());
   if (!ND->isOriginalNamespace())
     JOS.attribute("originalNamespace",
                   createBareDeclRef(ND->getOriginalNamespace()));
 }
 
 void JSONNodeDumper::VisitUsingDirectiveDecl(const UsingDirectiveDecl *UDD) {
   JOS.attribute("nominatedNamespace",
                 createBareDeclRef(UDD->getNominatedNamespace()));

clang/lib/AST/TextNodeDumper.cpp

void TextNodeDumper::VisitOMPCapturedExprDecl(const OMPCapturedExprDecl *D) {
   dumpName(D);
   dumpType(D->getType());
 }
 
 void TextNodeDumper::VisitNamespaceDecl(const NamespaceDecl *D) {
   dumpName(D);
   if (D->isInline())
     OS << " inline";
+  if (D->isNested())
+    OS << " nested";
   if (!D->isOriginalNamespace())
     dumpDeclRef(D->getOriginalNamespace(), "original");
 }
 
 void TextNodeDumper::VisitUsingDirectiveDecl(const UsingDirectiveDecl *D) {
   OS << ' ';
   dumpBareDeclRef(D->getNominatedNamespace());
 }

clang/lib/Parse/ParseDeclCXX.cpp

Diag(InlineLoc, getLangOpts().CPlusPlus11
                         : diag::ext_inline_namespace);
 
   // Enter a scope for the namespace.
   ParseScope NamespaceScope(this, Scope::DeclScope);
 
   UsingDirectiveDecl *ImplicitUsingDirectiveDecl = nullptr;
   Decl *NamespcDecl = Actions.ActOnStartNamespaceDef(
       getCurScope(), InlineLoc, NamespaceLoc, IdentLoc, Ident,
-      T.getOpenLocation(), attrs, ImplicitUsingDirectiveDecl);
+      T.getOpenLocation(), attrs, ImplicitUsingDirectiveDecl, false);
 
   PrettyDeclStackTraceEntry CrashInfo(Actions.Context, NamespcDecl,
                                       NamespaceLoc, "parsing namespace");
 
   // Parse the contents of the namespace.  This includes parsing recovery on
   // any improperly nested namespaces.
   ParseInnerNamespace(ExtraNSs, 0, InlineLoc, attrs, T);
 
void Parser::ParseInnerNamespace(const InnerNamespaceInfoList &InnerNSs,
   // Handle a nested namespace definition.
   // FIXME: Preserve the source information through to the AST rather than
   // desugaring it here.
   ParseScope NamespaceScope(this, Scope::DeclScope);
   UsingDirectiveDecl *ImplicitUsingDirectiveDecl = nullptr;
   Decl *NamespcDecl = Actions.ActOnStartNamespaceDef(
       getCurScope(), InnerNSs[index].InlineLoc, InnerNSs[index].NamespaceLoc,
       InnerNSs[index].IdentLoc, InnerNSs[index].Ident,
-      Tracker.getOpenLocation(), attrs, ImplicitUsingDirectiveDecl);
+      Tracker.getOpenLocation(), attrs, ImplicitUsingDirectiveDecl, true);
   assert(!ImplicitUsingDirectiveDecl &&
          "nested namespace definition cannot define anonymous namespace");
 
   ParseInnerNamespace(InnerNSs, ++index, InlineLoc, attrs, Tracker);
 
   NamespaceScope.Exit();
   Actions.ActOnFinishNamespaceDef(NamespcDecl, Tracker.getCloseLocation());
 }

clang/lib/Sema/HLSLExternalSemaSource.cpp

void HLSLExternalSemaSource::InitializeSema(Sema &S) {
   if (AST.getTranslationUnitDecl()->hasExternalLexicalStorage())
     (void)AST.getTranslationUnitDecl()->decls_begin();
 
   IdentifierInfo &HLSL = AST.Idents.get("hlsl", tok::TokenKind::identifier);
   LookupResult Result(S, &HLSL, SourceLocation(), Sema::LookupNamespaceName);
   NamespaceDecl *PrevDecl = nullptr;
   if (S.LookupQualifiedName(Result, AST.getTranslationUnitDecl()))
     PrevDecl = Result.getAsSingle<NamespaceDecl>();
-  HLSLNamespace = NamespaceDecl::Create(AST, AST.getTranslationUnitDecl(),
-                                        false, SourceLocation(),
-                                        SourceLocation(), &HLSL, PrevDecl);
+  HLSLNamespace = NamespaceDecl::Create(
+      AST, AST.getTranslationUnitDecl(), /*Inline=*/false, SourceLocation(),
+      SourceLocation(), &HLSL, PrevDecl, /*Nested=*/false);
   HLSLNamespace->setImplicit(true);
   HLSLNamespace->setHasExternalLexicalStorage();
   AST.getTranslationUnitDecl()->addDecl(HLSLNamespace);
 
   // Force external decls in the HLSL namespace to load from the PCH.
   (void)HLSLNamespace->getCanonicalDecl()->decls_begin();
   defineTrivialHLSLTypes();
   forwardDeclareHLSLTypes();

clang/lib/Sema/SemaDeclCXX.cpp

else
     S.Diag(Loc, diag::err_inline_namespace_mismatch);
 
   S.Diag(PrevNS->getLocation(), diag::note_previous_definition);
   *IsInline = PrevNS->isInline();
 }
 
 /// ActOnStartNamespaceDef - This is called at the start of a namespace
 /// definition.
-Decl *Sema::ActOnStartNamespaceDef(
-    Scope *NamespcScope, SourceLocation InlineLoc, SourceLocation NamespaceLoc,
-    SourceLocation IdentLoc, IdentifierInfo *II, SourceLocation LBrace,
-    const ParsedAttributesView &AttrList, UsingDirectiveDecl *&UD) {
+Decl *Sema::ActOnStartNamespaceDef(Scope *NamespcScope,
+                                   SourceLocation InlineLoc,
+                                   SourceLocation NamespaceLoc,
+                                   SourceLocation IdentLoc, IdentifierInfo *II,
+                                   SourceLocation LBrace,
+                                   const ParsedAttributesView &AttrList,
+                                   UsingDirectiveDecl *&UD, bool IsNested) {
   SourceLocation StartLoc = InlineLoc.isValid() ? InlineLoc : NamespaceLoc;
   // For anonymous namespace, take the location of the left brace.
   SourceLocation Loc = II ? IdentLoc : LBrace;
   bool IsInline = InlineLoc.isValid();
   bool IsInvalid = false;
   bool IsStd = false;
   bool AddToKnown = false;
   Scope *DeclRegionScope = NamespcScope->getParent();
if (TranslationUnitDecl *TU = dyn_cast<TranslationUnitDecl>(Parent)) {
       PrevNS = ND->getAnonymousNamespace();
     }
 
     if (PrevNS && IsInline != PrevNS->isInline())
       DiagnoseNamespaceInlineMismatch(*this, NamespaceLoc, NamespaceLoc, II,
                                       &IsInline, PrevNS);
   }
 
-  NamespaceDecl *Namespc = NamespaceDecl::Create(Context, CurContext, IsInline,
-                                                 StartLoc, Loc, II, PrevNS);
+  NamespaceDecl *Namespc = NamespaceDecl::Create(
+      Context, CurContext, IsInline, StartLoc, Loc, II, PrevNS, IsNested);
   if (IsInvalid)
     Namespc->setInvalidDecl();
 
   ProcessDeclAttributeList(DeclRegionScope, Namespc, AttrList);
   AddPragmaAttributes(DeclRegionScope, Namespc);
 
   // FIXME: Should we be merging attributes?
   if (const VisibilityAttr *Attr = Namespc->getAttr<VisibilityAttr>())
QualType Sema::CheckComparisonCategoryType(ComparisonCategoryType Kind,
   return Info->getType();
 }
 
 /// Retrieve the special "std" namespace, which may require us to
 /// implicitly define the namespace.
 NamespaceDecl *Sema::getOrCreateStdNamespace() {
   if (!StdNamespace) {
     // The "std" namespace has not yet been defined, so build one implicitly.
-    StdNamespace = NamespaceDecl::Create(Context,
-                                         Context.getTranslationUnitDecl(),
-                                         /*Inline=*/false,
-                                         SourceLocation(), SourceLocation(),
-                                         &PP.getIdentifierTable().get("std"),
-                                         /*PrevDecl=*/nullptr);
+    StdNamespace = NamespaceDecl::Create(
+        Context, Context.getTranslationUnitDecl(),
+        /*Inline=*/false, SourceLocation(), SourceLocation(),
+        /*PrevDecl=*/nullptr, /*Nested=*/false);
     getStdNamespace()->setImplicit(true);
   }
 
   return getStdNamespace();
 }
 
 bool Sema::isStdInitializerList(QualType Ty, QualType *Element) {
   assert(getLangOpts().CPlusPlus &&

clang/lib/Serialization/ASTReaderDecl.cpp

void ASTDeclReader::VisitLabelDecl(LabelDecl *D) {
   VisitNamedDecl(D);
   D->setLocStart(readSourceLocation());
 }
 
 void ASTDeclReader::VisitNamespaceDecl(NamespaceDecl *D) {
   RedeclarableResult Redecl = VisitRedeclarable(D);
   VisitNamedDecl(D);
   D->setInline(Record.readInt());
+  D->setNested(Record.readInt());
   D->LocStart = readSourceLocation();
   D->RBraceLoc = readSourceLocation();
 
   // Defer loading the anonymous namespace until we've finished merging
   // this namespace; loading it might load a later declaration of the
   // same namespace, and we have an invariant that older declarations
   // get merged before newer ones try to merge.
   GlobalDeclID AnonNamespace = 0;
   if (Redecl.getFirstID() == ThisDeclID) {
     AnonNamespace = readDeclID();
   } else {
     // Link this namespace back to the first declaration, which has already
     // been deserialized.
-    D->AnonOrFirstNamespaceAndInline.setPointer(D->getFirstDecl());
+    D->AnonOrFirstNamespaceAndFlags.setPointer(D->getFirstDecl());
   }
 
   mergeRedeclarable(D, Redecl);
 
   if (AnonNamespace) {
     // Each module has its own anonymous namespace, which is disjoint from
     // any other module's anonymous namespaces, so don't attach the anonymous
     // namespace at all.
if (ExistingCanon != DCanon) {
     D->First = ExistingCanon;
     ExistingCanon->Used |= D->Used;
     D->Used = false;
 
     // When we merge a namespace, update its pointer to the first namespace.
     // We cannot have loaded any redeclarations of this declaration yet, so
     // there's nothing else that needs to be updated.
     if (auto *Namespace = dyn_cast<NamespaceDecl>(D))
-      Namespace->AnonOrFirstNamespaceAndInline.setPointer(
-          assert_cast<NamespaceDecl*>(ExistingCanon));
+      Namespace->AnonOrFirstNamespaceAndFlags.setPointer(
+          assert_cast<NamespaceDecl *>(ExistingCanon));
 
     // When we merge a template, merge its pattern.
     if (auto *DTemplate = dyn_cast<RedeclarableTemplateDecl>(D))
       mergeTemplatePattern(
           DTemplate, assert_cast<RedeclarableTemplateDecl *>(ExistingCanon),
           Redecl.isKeyDecl());
 
     // If this declaration is a key declaration, make a note of that.

clang/lib/Serialization/ASTWriterDecl.cpp

void ASTDeclWriter::VisitLabelDecl(LabelDecl *D) {
   Code = serialization::DECL_LABEL;
 }
 
 
 void ASTDeclWriter::VisitNamespaceDecl(NamespaceDecl *D) {
   VisitRedeclarable(D);
   VisitNamedDecl(D);
   Record.push_back(D->isInline());
+  Record.push_back(D->isNested());
   Record.AddSourceLocation(D->getBeginLoc());
   Record.AddSourceLocation(D->getRBraceLoc());
 
   if (D->isOriginalNamespace())
     Record.AddDeclRef(D->getAnonymousNamespace());
   Code = serialization::DECL_NAMESPACE;
 
   if (Writer.hasChain() && D->isAnonymousNamespace() &&

clang/test/AST/ast-dump-decl.cpp

 // CHECK:      NamespaceDecl{{.*}} TestNamespaceDecl
 // CHECK-NEXT:   original Namespace
 // CHECK-NEXT:   VarDecl
 
 inline namespace TestNamespaceDeclInline {
 }
 // CHECK:      NamespaceDecl{{.*}} TestNamespaceDeclInline inline
 
+namespace TestNestedNameSpace::Nested {
+}
+// CHECK:      NamespaceDecl{{.*}} TestNestedNameSpace
+// CHECK:      NamespaceDecl{{.*}} Nested nested{{\s*$}}
+
+namespace TestMultipleNested::SecondLevelNested::Nested {
+}
+// CHECK:      NamespaceDecl{{.*}} TestMultipleNested
+// CHECK:      NamespaceDecl{{.*}} SecondLevelNested nested
+// CHECK:      NamespaceDecl{{.*}} Nested nested{{\s*$}}
+
+namespace TestInlineNested::inline SecondLevel::inline Nested {
+}
+// CHECK:      NamespaceDecl{{.*}} TestInlineNested
+// CHECK:      NamespaceDecl{{.*}} SecondLevel inline nested
+// CHECK:      NamespaceDecl{{.*}} Nested inline nested{{\s*$}}
+
 namespace testUsingDirectiveDecl {
   namespace A {
   }
 }
 namespace TestUsingDirectiveDecl {
   using namespace testUsingDirectiveDecl::A;
 }
 // CHECK:      NamespaceDecl{{.*}} TestUsingDirectiveDecl

 
 // CHECK: VarDecl {{.*}} Test 'int' extern
 // CHECK-NOT: FullComment
 // CHECK: VarDecl {{.*}} Test 'int' extern
 // CHECK: `-FullComment
 // CHECK:   `-ParagraphComment
 // CHECK:       `-TextComment
 // CHECK: VarDecl {{.*}} Test 'int' extern
 // CHECK-NOT: FullComment

clang/test/AST/ast-dump-namespace-json.cpp

 // CHECK-NEXT:     "end": {
 // CHECK-NEXT:      "offset": {{[0-9]+}},
 // CHECK-NEXT:      "line": 15,
 // CHECK-NEXT:      "col": 1,
 // CHECK-NEXT:      "tokLen": 1
 // CHECK-NEXT:     }
 // CHECK-NEXT:    },
 // CHECK-NEXT:    "name": "quux"
+// CHECK-NEXT:    "isNested": true
 // CHECK-NEXT:   }
 // CHECK-NEXT:  ]
 // CHECK-NEXT: }
 
 // CHECK-NOT: {{^}}Dumping
 // CHECK:  "kind": "NamespaceDecl",
 // CHECK-NEXT:  "loc": {
 // CHECK-NEXT:   "offset": {{[0-9]+}},

 // CHECK-NEXT:   },
 // CHECK-NEXT:   "end": {
 // CHECK-NEXT:    "offset": {{[0-9]+}},
 // CHECK-NEXT:    "line": 18,
 // CHECK-NEXT:    "col": 1,
 // CHECK-NEXT:    "tokLen": 1
 // CHECK-NEXT:   }
 // CHECK-NEXT:  },
-// CHECK-NEXT:  "name": "quux",
+// CHECK-NEXT:  "name": "quux"
 // CHECK-NEXT:  "inner": [
 // CHECK-NEXT:   {
 // CHECK-NEXT:    "id": "0x{{.*}}",
 // CHECK-NEXT:    "kind": "NamespaceDecl",
 // CHECK-NEXT:    "loc": {
 // CHECK-NEXT:     "offset": {{[0-9]+}},
 // CHECK-NEXT:     "line": 17,
 // CHECK-NEXT:     "col": 24,
 // CHECK-NEXT:     "tokLen": 7
 // CHECK-NEXT:    },
 // CHECK-NEXT:    "range": {
 // CHECK-NEXT:     "begin": {
 // CHECK-NEXT:      "offset": {{[0-9]+}},
 // CHECK-NEXT:      "col": 17,
 // CHECK-NEXT:      "tokLen": 6
 // CHECK-NEXT:     },
 // CHECK-NEXT:     "end": {
 // CHECK-NEXT:      "offset": {{[0-9]+}},
 // CHECK-NEXT:      "line": 18,
 // CHECK-NEXT:      "col": 1,
 // CHECK-NEXT:      "tokLen": 1
 // CHECK-NEXT:     }
 // CHECK-NEXT:    },
 // CHECK-NEXT:    "name": "frobble",
-// CHECK-NEXT:    "isInline": true
+// CHECK-NEXT:    "isInline": true,
+// CHECK-NEXT:    "isNested": true
 // CHECK-NEXT:   }
 // CHECK-NEXT:  ]
 // CHECK-NEXT: }

clang/unittests/Sema/ExternalSemaSourceTest.cpp

if (CurrentSema && Typo.getName().getAsString() == CorrectFrom) {
       if (SS)
         DestContext = CurrentSema->computeDeclContext(*SS, EnteringContext);
       if (!DestContext)
         DestContext = Context.getTranslationUnitDecl();
       IdentifierInfo *ToIdent =
           CurrentSema->getPreprocessor().getIdentifierInfo(CorrectTo);
       NamespaceDecl *NewNamespace =
           NamespaceDecl::Create(Context, DestContext, false, Typo.getBeginLoc(),
-                                Typo.getLoc(), ToIdent, nullptr);
+                                Typo.getLoc(), ToIdent, nullptr, false);
       DestContext->addDecl(NewNamespace);
       TypoCorrection Correction(ToIdent);
       Correction.addCorrectionDecl(NewNamespace);
       return Correction;
     }
     return TypoCorrection();
   }