[C++20] [Modules] Support module level lookup

clang/docs/ReleaseNotes.rst

@@ -316,6 +316,8 @@ C++23 Feature Support
 C++20 Feature Support
 ^^^^^^^^^^^^^^^^^^^^^
 
+- Implemented module level lookup for C++20 modules. (#GH90154)
+
 
 Resolutions to C++ Defect Reports
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

clang/include/clang/AST/DeclBase.h

@@ -836,6 +836,10 @@ class alignas(8) Decl {
     return isFromASTFile() ? getImportedOwningModule() : getLocalOwningModule();
   }
 
+  /// Get the top level owning named module that owns this declaration if any.
+  /// \returns nullptr if the declaration is not owned by a named module.
+  Module *getTopLevelOwningNamedModule() const;
+
   /// Get the module that owns this declaration for linkage purposes.
   /// There only ever is such a standard C++ module.
   Module *getOwningModuleForLinkage() const;
@@ -2711,6 +2715,12 @@ class DeclContext {
                    bool Deserialize = false) const;
 
 private:
+  /// Lookup all external visible declarations and the external declarations
+  /// within the same module specified by \c NamedModule. We can't
+  /// get it from \c this since the same declaration may be declared in
+  /// multiple modules. e.g., namespace.
+  lookup_result lookupImpl(DeclarationName Name, Module *NamedModule) const;
+
   /// Whether this declaration context has had externally visible
   /// storage added since the last lookup. In this case, \c LookupPtr's
   /// invariant may not hold and needs to be fixed before we perform

clang/include/clang/AST/ExternalASTMerger.h

@@ -141,7 +141,8 @@ class ExternalASTMerger : public ExternalASTSource {
 
   /// Implementation of the ExternalASTSource API.
   bool FindExternalVisibleDeclsByName(const DeclContext *DC,
-                                      DeclarationName Name) override;
+                                      DeclarationName Name,
+                                      Module *NamedModule) override;
 
   /// Implementation of the ExternalASTSource API.
   void

clang/include/clang/AST/ExternalASTSource.h

@@ -51,6 +51,7 @@ class RecordDecl;
 class Selector;
 class Stmt;
 class TagDecl;
+class Module;
 
 /// Abstract interface for external sources of AST nodes.
 ///
@@ -145,12 +146,20 @@ class ExternalASTSource : public RefCountedBase<ExternalASTSource> {
   /// Find all declarations with the given name in the given context,
   /// and add them to the context by calling SetExternalVisibleDeclsForName
   /// or SetNoExternalVisibleDeclsForName.
-  /// \return \c true if any declarations might have been found, \c false if
-  /// we definitely have no declarations with tbis name.
+  /// \param DC the context for lookup.
+  /// \param Name the name of the declarations to find.
+  /// \param NamedModule find declarations visible to the given module
+  /// \c NamedModule . This may be different from owning module of \c DC since
+  /// there are declarations (e.g., namespace declaration) can appear in
+  /// multiple modules.
+  ///
+  /// \return \c true if any declarations might have been found, and \c false
+  /// if we definitely have no declarations with this name.
   ///
   /// The default implementation of this method is a no-op returning \c false.
-  virtual bool
-  FindExternalVisibleDeclsByName(const DeclContext *DC, DeclarationName Name);
+  virtual bool FindExternalVisibleDeclsByName(const DeclContext *DC,
+                                              DeclarationName Name,
+                                              Module *NamedModule);
 
   /// Load all the external specializations for the Decl \param D if \param
   /// OnlyPartial is false. Otherwise, load all the external **partial**

clang/include/clang/Sema/MultiplexExternalSemaSource.h

@@ -95,7 +95,8 @@ class MultiplexExternalSemaSource : public ExternalSemaSource {
   /// Find all declarations with the given name in the
   /// given context.
   bool FindExternalVisibleDeclsByName(const DeclContext *DC,
-                                      DeclarationName Name) override;
+                                      DeclarationName Name,
+                                      Module *NamedModule) override;
 
   bool LoadExternalSpecializations(const Decl *D, bool OnlyPartial) override;
 

clang/include/clang/Serialization/ASTBitCodes.h

@@ -738,6 +738,8 @@ enum ASTRecordTypes {
   CXX_ADDED_TEMPLATE_SPECIALIZATION = 74,
 
   CXX_ADDED_TEMPLATE_PARTIAL_SPECIALIZATION = 75,
+
+  UPDATE_MODULE_LOCAL_VISIBLE = 76,
 };
 
 /// Record types used within a source manager block.
@@ -1334,6 +1336,10 @@ enum DeclCode {
   /// into a DeclContext via DeclContext::lookup.
   DECL_CONTEXT_VISIBLE,
 
+  /// A record containing the set of declarations that are
+  /// only visible from DeclContext in the same module.
+  DECL_CONTEXT_MODULE_LOCAL_VISIBLE,
+
   /// A LabelDecl record.
   DECL_LABEL,
 

clang/include/clang/Serialization/ASTReader.h

@@ -353,6 +353,7 @@ class ASTIdentifierLookupTrait;
 
 /// The on-disk hash table(s) used for DeclContext name lookup.
 struct DeclContextLookupTable;
+struct ModuleLocalLookupTable;
 
 /// The on-disk hash table(s) used for specialization decls.
 struct LazySpecializationInfoLookupTable;
@@ -523,9 +524,14 @@ class ASTReader
   /// in the chain.
   DeclUpdateOffsetsMap DeclUpdateOffsets;
 
+  struct LookupBlockOffsets {
+    uint64_t LexicalOffset;
+    uint64_t VisibleOffset;
+    uint64_t ModuleLocalOffset;
+  };
+
   using DelayedNamespaceOffsetMapTy =
-      llvm::DenseMap<GlobalDeclID, std::pair</*LexicalOffset*/ uint64_t,
-                                             /*VisibleOffset*/ uint64_t>>;
+      llvm::DenseMap<GlobalDeclID, LookupBlockOffsets>;
 
   /// Mapping from global declaration IDs to the lexical and visible block
   /// offset for delayed namespace in reduced BMI.
@@ -631,6 +637,9 @@ class ASTReader
   /// Map from a DeclContext to its lookup tables.
   llvm::DenseMap<const DeclContext *,
                  serialization::reader::DeclContextLookupTable> Lookups;
+  llvm::DenseMap<const DeclContext *,
+                 serialization::reader::ModuleLocalLookupTable>
+      ModuleLocalLookups;
 
   using SpecLookupTableTy =
       llvm::DenseMap<const Decl *,
@@ -659,6 +668,8 @@ class ASTReader
   /// Updates to the visible declarations of declaration contexts that
   /// haven't been loaded yet.
   llvm::DenseMap<GlobalDeclID, DeclContextVisibleUpdates> PendingVisibleUpdates;
+  llvm::DenseMap<GlobalDeclID, DeclContextVisibleUpdates>
+      PendingModuleLocalVisibleUpdates;
 
   using SpecializationsUpdate = SmallVector<UpdateData, 1>;
   using SpecializationsUpdateMap =
@@ -696,7 +707,8 @@ class ASTReader
   /// Read the record that describes the visible contents of a DC.
   bool ReadVisibleDeclContextStorage(ModuleFile &M,
                                      llvm::BitstreamCursor &Cursor,
-                                     uint64_t Offset, GlobalDeclID ID);
+                                     uint64_t Offset, GlobalDeclID ID,
+                                     bool IsModuleLocal);
 
   bool ReadSpecializations(ModuleFile &M, llvm::BitstreamCursor &Cursor,
                            uint64_t Offset, Decl *D, bool IsPartial);
@@ -1132,6 +1144,10 @@ class ASTReader
   /// Number of visible decl contexts read/total.
   unsigned NumVisibleDeclContextsRead = 0, TotalVisibleDeclContexts = 0;
 
+  /// Number of module local visible decl contexts read/total.
+  unsigned NumModuleLocalVisibleDeclContexts = 0,
+           TotalModuleLocalVisibleDeclContexts = 0;
+
   /// Total size of modules, in bits, currently loaded
   uint64_t TotalModulesSizeInBits = 0;
 
@@ -1444,6 +1460,9 @@ class ASTReader
   const serialization::reader::DeclContextLookupTable *
   getLoadedLookupTables(DeclContext *Primary) const;
 
+  const serialization::reader::ModuleLocalLookupTable *
+  getModuleLocalLookupTables(DeclContext *Primary) const;
+
   /// Get the loaded specializations lookup tables for \p D,
   /// if any.
   serialization::reader::LazySpecializationInfoLookupTable *
@@ -2119,7 +2138,8 @@ class ASTReader
   /// The current implementation of this method just loads the entire
   /// lookup table as unmaterialized references.
   bool FindExternalVisibleDeclsByName(const DeclContext *DC,
-                                      DeclarationName Name) override;
+                                      DeclarationName Name,
+                                      Module *NamedModule) override;
 
   /// Read all of the declarations lexically stored in a
   /// declaration context.
@@ -2607,6 +2627,10 @@ inline bool shouldSkipCheckingODR(const Decl *D) {
          (D->isFromGlobalModule() || D->isFromHeaderUnit());
 }
 
+/// Calculate a hash value for the primary module name of the given module.
+/// \returns std::nullopt if M is not a C++ standard module.
+std::optional<unsigned> getPrimaryModuleHash(const Module *M);
+
 } // namespace clang
 
 #endif // LLVM_CLANG_SERIALIZATION_ASTREADER_H

clang/include/clang/Serialization/ASTWriter.h

@@ -492,6 +492,10 @@ class ASTWriter : public ASTDeserializationListener,
   /// file.
   unsigned NumVisibleDeclContexts = 0;
 
+  /// The number of module local visible declcontexts written to the AST
+  /// file.
+  unsigned NumModuleLocalDeclContexts = 0;
+
   /// A mapping from each known submodule to its ID number, which will
   /// be a positive integer.
   llvm::DenseMap<const Module *, unsigned> SubmoduleIDs;
@@ -587,11 +591,15 @@ class ASTWriter : public ASTDeserializationListener,
   uint64_t WriteSpecializationInfoLookupTable(
       const NamedDecl *D, llvm::SmallVectorImpl<const Decl *> &Specializations,
       bool IsPartial);
-  void GenerateNameLookupTable(ASTContext &Context, const DeclContext *DC,
-                               llvm::SmallVectorImpl<char> &LookupTable);
+  void
+  GenerateNameLookupTable(ASTContext &Context, const DeclContext *DC,
+                          llvm::SmallVectorImpl<char> &LookupTable,
+                          llvm::SmallVectorImpl<char> &ModuleLocalLookupTable);
   uint64_t WriteDeclContextLexicalBlock(ASTContext &Context,
                                         const DeclContext *DC);
-  uint64_t WriteDeclContextVisibleBlock(ASTContext &Context, DeclContext *DC);
+  void WriteDeclContextVisibleBlock(ASTContext &Context, DeclContext *DC,
+                                    uint64_t &VisibleBlockOffset,
+                                    uint64_t &ModuleLocalBlockOffset);
   void WriteTypeDeclOffsets();
   void WriteFileDeclIDsMap();
   void WriteComments(ASTContext &Context);
@@ -624,7 +632,9 @@ class ASTWriter : public ASTDeserializationListener,
   unsigned DeclParmVarAbbrev = 0;
   unsigned DeclContextLexicalAbbrev = 0;
   unsigned DeclContextVisibleLookupAbbrev = 0;
+  unsigned DeclModuleLocalVisibleLookupAbbrev = 0;
   unsigned UpdateVisibleAbbrev = 0;
+  unsigned ModuleLocalUpdateVisibleAbbrev = 0;
   unsigned DeclRecordAbbrev = 0;
   unsigned DeclTypedefAbbrev = 0;
   unsigned DeclVarAbbrev = 0;

clang/lib/AST/DeclBase.cpp

@@ -1850,15 +1850,28 @@ void DeclContext::buildLookupImpl(DeclContext *DCtx, bool Internal) {
   }
 }
 
+Module *Decl::getTopLevelOwningNamedModule() const {
+  if (getOwningModule() &&
+      getOwningModule()->getTopLevelModule()->isNamedModule())
+    return getOwningModule()->getTopLevelModule();
+
+  return nullptr;
+}
+
 DeclContext::lookup_result
 DeclContext::lookup(DeclarationName Name) const {
+  return lookupImpl(Name, cast<Decl>(this)->getTopLevelOwningNamedModule());
+}
+
+DeclContext::lookup_result DeclContext::lookupImpl(DeclarationName Name,
+                                                   Module *NamedModule) const {
   // For transparent DeclContext, we should lookup in their enclosing context.
   if (getDeclKind() == Decl::LinkageSpec || getDeclKind() == Decl::Export)
-    return getParent()->lookup(Name);
+    return getParent()->lookupImpl(Name, NamedModule);
 
   const DeclContext *PrimaryContext = getPrimaryContext();
   if (PrimaryContext != this)
-    return PrimaryContext->lookup(Name);
+    return PrimaryContext->lookupImpl(Name, NamedModule);
 
   // If we have an external source, ensure that any later redeclarations of this
   // context have been loaded, since they may add names to the result of this
@@ -1889,7 +1902,8 @@ DeclContext::lookup(DeclarationName Name) const {
     if (!R.second && !R.first->second.hasExternalDecls())
       return R.first->second.getLookupResult();
 
-    if (Source->FindExternalVisibleDeclsByName(this, Name) || !R.second) {
+    if (Source->FindExternalVisibleDeclsByName(this, Name, NamedModule) ||
+        !R.second) {
       if (StoredDeclsMap *Map = LookupPtr) {
         StoredDeclsMap::iterator I = Map->find(Name);
         if (I != Map->end())
@@ -2115,7 +2129,8 @@ void DeclContext::makeDeclVisibleInContextImpl(NamedDecl *D, bool Internal) {
     if (ExternalASTSource *Source = getParentASTContext().getExternalSource())
       if (hasExternalVisibleStorage() &&
           Map->find(D->getDeclName()) == Map->end())
-        Source->FindExternalVisibleDeclsByName(this, D->getDeclName());
+        Source->FindExternalVisibleDeclsByName(
+            this, D->getDeclName(), D->getTopLevelOwningNamedModule());
 
   // Insert this declaration into the map.
   StoredDeclsList &DeclNameEntries = (*Map)[D->getDeclName()];

clang/lib/AST/ExternalASTMerger.cpp

@@ -472,7 +472,8 @@ static bool importSpecializationsIfNeeded(Decl *D, ASTImporter *Importer) {
 }
 
 bool ExternalASTMerger::FindExternalVisibleDeclsByName(const DeclContext *DC,
-                                                       DeclarationName Name) {
+                                                       DeclarationName Name,
+                                                       Module *NamedModule) {
   llvm::SmallVector<NamedDecl *, 1> Decls;
   llvm::SmallVector<Candidate, 4> Candidates;
 

clang/lib/AST/ExternalASTSource.cpp

@@ -90,9 +90,9 @@ ExternalASTSource::GetExternalCXXBaseSpecifiers(uint64_t Offset) {
   return nullptr;
 }
 
-bool
-ExternalASTSource::FindExternalVisibleDeclsByName(const DeclContext *DC,
-                                                  DeclarationName Name) {
+bool ExternalASTSource::FindExternalVisibleDeclsByName(const DeclContext *DC,
+                                                       DeclarationName Name,
+                                                       Module *NamedModule) {
   return false;
 }
 

clang/lib/Interpreter/CodeCompletion.cpp

@@ -228,7 +228,8 @@ class ExternalSource : public clang::ExternalASTSource {
   ExternalSource(ASTContext &ChildASTCtxt, FileManager &ChildFM,
                  ASTContext &ParentASTCtxt, FileManager &ParentFM);
   bool FindExternalVisibleDeclsByName(const DeclContext *DC,
-                                      DeclarationName Name) override;
+                                      DeclarationName Name,
+                                      Module *NamedModule) override;
   void
   completeVisibleDeclsMap(const clang::DeclContext *childDeclContext) override;
 };
@@ -271,7 +272,8 @@ ExternalSource::ExternalSource(ASTContext &ChildASTCtxt, FileManager &ChildFM,
 }
 
 bool ExternalSource::FindExternalVisibleDeclsByName(const DeclContext *DC,
-                                                    DeclarationName Name) {
+                                                    DeclarationName Name,
+                                                    Module *NamedModule) {
 
   IdentifierTable &ParentIdTable = ParentASTCtxt.Idents;
 

clang/lib/Sema/MultiplexExternalSemaSource.cpp

@@ -107,11 +107,12 @@ MultiplexExternalSemaSource::hasExternalDefinitions(const Decl *D) {
   return EK_ReplyHazy;
 }
 
-bool MultiplexExternalSemaSource::
-FindExternalVisibleDeclsByName(const DeclContext *DC, DeclarationName Name) {
+bool MultiplexExternalSemaSource::FindExternalVisibleDeclsByName(
+    const DeclContext *DC, DeclarationName Name, Module *NamedModule) {
   bool AnyDeclsFound = false;
   for (size_t i = 0; i < Sources.size(); ++i)
-    AnyDeclsFound |= Sources[i]->FindExternalVisibleDeclsByName(DC, Name);
+    AnyDeclsFound |=
+        Sources[i]->FindExternalVisibleDeclsByName(DC, Name, NamedModule);
   return AnyDeclsFound;
 }