1 files changed, 132 insertions, 7 deletions

diff --git a/include/clang/AST/ExternalASTMerger.h b/include/clang/AST/ExternalASTMerger.h
index 51d0c30ad23b..81492aec6e13 100644
--- a/include/clang/AST/ExternalASTMerger.h
+++ b/include/clang/AST/ExternalASTMerger.h
@@ -16,34 +16,159 @@
 
 #include "clang/AST/ASTImporter.h"
 #include "clang/AST/ExternalASTSource.h"
+#include "llvm/Support/raw_ostream.h"
 
 namespace clang {
 
+/// ExternalASTSource implementation that merges information from several
+/// ASTContexts.
+///
+/// ExtermalASTMerger maintains a vector of ASTImporters that it uses to import
+/// (potentially incomplete) Decls and DeclContexts from the source ASTContexts
+/// in response to ExternalASTSource API calls.
+///
+/// When lookup occurs in the resulting imported DeclContexts, the original
+/// DeclContexts need to be queried.  Roughly, there are three cases here:
+///
+/// - The DeclContext of origin can be found by simple name lookup.  In this
+///   case, no additional state is required.
+///
+/// - The DeclContext of origin is different from what would be found by name
+///   lookup.  In this case, Origins contains an entry overriding lookup and
+///   specifying the correct pair of DeclContext/ASTContext.
+///
+/// - The DeclContext of origin was determined by another ExterenalASTMerger. 
+///   (This is possible when the source ASTContext for one of the Importers has
+///   its own ExternalASTMerger).  The origin must be properly forwarded in this
+///   case.
+///
+/// ExternalASTMerger's job is to maintain the data structures necessary to
+/// allow this.  The data structures themselves can be extracted (read-only) and
+/// copied for re-use.
 class ExternalASTMerger : public ExternalASTSource {
 public:
-  struct ImporterPair {
-    std::unique_ptr<ASTImporter> Forward;
-    std::unique_ptr<ASTImporter> Reverse;
+  /// A single origin for a DeclContext.  Unlike Decls, DeclContexts do
+  /// not allow their containing ASTContext to be determined in all cases.
+  struct DCOrigin {
+    DeclContext *DC;
+    ASTContext *AST;
   };
 
+  typedef std::map<const DeclContext *, DCOrigin> OriginMap;
+  typedef std::vector<std::unique_ptr<ASTImporter>> ImporterVector;
 private:
-  std::vector<ImporterPair> Importers;
+  /// One importer exists for each source.  
+  ImporterVector Importers;
+  /// Overrides in case name lookup would return nothing or would return
+  /// the wrong thing.
+  OriginMap Origins;
+  /// The installed log stream.
+  llvm::raw_ostream *LogStream;
 
 public:
-  struct ImporterEndpoint {
+  /// The target for an ExternalASTMerger.
+  ///
+  /// ASTImporters require both ASTContext and FileManager to be able to
+  /// import SourceLocations properly.
+  struct ImporterTarget {
     ASTContext &AST;
     FileManager &FM;
   };
-  ExternalASTMerger(const ImporterEndpoint &Target,
-                    llvm::ArrayRef<ImporterEndpoint> Sources);
+  /// A source for an ExternalASTMerger.
+  ///
+  /// ASTImporters require both ASTContext and FileManager to be able to
+  /// import SourceLocations properly.  Additionally, when import occurs for
+  /// a DeclContext whose origin has been overridden, then this
+  /// ExternalASTMerger must be able to determine that.
+  struct ImporterSource {
+    ASTContext &AST;
+    FileManager &FM;
+    const OriginMap &OM;
+  };
 
+private:
+  /// The target for this ExtenralASTMerger.
+  ImporterTarget Target;
+
+public:
+  ExternalASTMerger(const ImporterTarget &Target,
+                    llvm::ArrayRef<ImporterSource> Sources);
+
+  /// Add a set of ASTContexts as possible origins.
+  ///
+  /// Usually the set will be initialized in the constructor, but long-lived
+  /// ExternalASTMergers may neeed to import from new sources (for example,
+  /// newly-parsed source files).
+  ///
+  /// Ensures that Importers does not gain duplicate entries as a result.
+  void AddSources(llvm::ArrayRef<ImporterSource> Sources);
+
+  /// Remove a set of ASTContexts as possible origins.
+  ///
+  /// Sometimes an origin goes away (for example, if a source file gets
+  /// superseded by a newer version). 
+  ///
+  /// The caller is responsible for ensuring that this doesn't leave
+  /// DeclContexts that can't be completed.
+  void RemoveSources(llvm::ArrayRef<ImporterSource> Sources);
+
+  /// Implementation of the ExternalASTSource API.
   bool FindExternalVisibleDeclsByName(const DeclContext *DC,
                                       DeclarationName Name) override;
 
+  /// Implementation of the ExternalASTSource API.
   void
   FindExternalLexicalDecls(const DeclContext *DC,
                            llvm::function_ref<bool(Decl::Kind)> IsKindWeWant,
                            SmallVectorImpl<Decl *> &Result) override;
+
+  /// Implementation of the ExternalASTSource API.
+  void CompleteType(TagDecl *Tag) override;
+
+  /// Implementation of the ExternalASTSource API.
+  void CompleteType(ObjCInterfaceDecl *Interface) override;
+
+  /// Returns true if DC can be found in any source AST context.
+  bool CanComplete(DeclContext *DC);
+
+  /// Records an origin in Origins only if name lookup would find
+  /// something different or nothing at all.
+  void MaybeRecordOrigin(const DeclContext *ToDC, DCOrigin Origin);
+
+  /// Regardless of any checks, override the Origin for a DeclContext.
+  void ForceRecordOrigin(const DeclContext *ToDC, DCOrigin Origin);
+
+  /// Get a read-only view of the Origins map, for use in constructing
+  /// an ImporterSource for another ExternalASTMerger.
+  const OriginMap &GetOrigins() { return Origins; }
+
+  /// Returns true if Importers contains an ASTImporter whose source is
+  /// OriginContext.
+  bool HasImporterForOrigin(ASTContext &OriginContext);
+
+  /// Returns a reference to the ASTRImporter from Importers whose origin
+  /// is OriginContext.  This allows manual import of ASTs while preserving the
+  /// OriginMap correctly.
+  ASTImporter &ImporterForOrigin(ASTContext &OriginContext);
+
+  /// Sets the current log stream.
+  void SetLogStream(llvm::raw_string_ostream &Stream) { LogStream = &Stream; }
+private:
+  /// Records and origin in Origins.
+  void RecordOriginImpl(const DeclContext *ToDC, DCOrigin Origin,
+                                  ASTImporter &importer);
+
+  /// Performs an action for every DeclContext that is identified as
+  /// corresponding (either by forced origin or by name lookup) to DC.
+  template <typename CallbackType>
+  void ForEachMatchingDC(const DeclContext *DC, CallbackType Callback);
+
+public: 
+  /// Log something if there is a logging callback installed.
+  llvm::raw_ostream &logs() { return *LogStream; }
+
+  /// True if the log stream is not llvm::nulls();
+  bool LoggingEnabled() { return LogStream != &llvm::nulls(); }
 };
 
 } // end namespace clang