[NamedLazyMemberLoading] Add loadNamedMembers method and stub implementations.

include/swift/AST/LazyResolver.h

@@ -218,12 +218,23 @@ class alignas(void*) LazyMemberLoader {
 public:
   virtual ~LazyMemberLoader() = default;
 
-  /// Populates the given vector with all member decls for \p D.
+  /// Populates a given decl \p D with all of its members.
   ///
   /// The implementation should add the members to D.
   virtual void
   loadAllMembers(Decl *D, uint64_t contextData) = 0;
 
+  /// Populates a vector with all members of \p D that have DeclName
+  /// matching \p N.
+  ///
+  /// Returns true if an error occurred \em or the set of returned
+  /// \p Members is otherwise incomplete, due to implementation limitations
+  /// (eg. the implementation is unable to do named lookup at all, or within
+  /// the particular type of Decl that \p D is).
+  virtual bool
+  loadNamedMembers(const Decl *D, DeclName N, uint64_t contextData,
+                   TinyPtrVector<ValueDecl *> &Members) = 0;
+
   /// Populates the given vector with all conformances for \p D.
   ///
   /// The implementation should \em not call setConformances on \p D.

include/swift/Serialization/ModuleFile.h

@@ -700,6 +700,11 @@ public:
   virtual void loadAllMembers(Decl *D,
                               uint64_t contextData) override;
 
+  virtual bool
+  loadNamedMembers(const Decl *D, DeclName N,
+                   uint64_t contextData,
+                   TinyPtrVector<ValueDecl *> &Members) override;
+
   virtual void
   loadAllConformances(const Decl *D, uint64_t contextData,
                     SmallVectorImpl<ProtocolConformance*> &Conforms) override;

lib/ClangImporter/ImportDecl.cpp

@@ -7994,6 +7994,13 @@ ClangImporter::Implementation::loadAllMembers(Decl *D, uint64_t extra) {
   loadAllMembersIntoExtension(D, extra);
 }
 
+bool ClangImporter::Implementation::loadNamedMembers(
+    const Decl *D, DeclName N, uint64_t contextData,
+    TinyPtrVector<ValueDecl *> &Members) {
+  // Not presently supported.
+  return true;
+}
+
 void ClangImporter::Implementation::loadAllMembersIntoExtension(
     Decl *D, uint64_t extra) {
   // We have extension.

lib/ClangImporter/ImporterImpl.h

@@ -1122,6 +1122,10 @@ public:
   virtual void
   loadAllMembers(Decl *D, uint64_t unused) override;
 
+  virtual bool
+  loadNamedMembers(const Decl *D, DeclName N, uint64_t contextData,
+                   TinyPtrVector<ValueDecl *> &Members) override;
+
 private:
   void
   loadAllMembersOfObjcContainer(Decl *D,

lib/Serialization/Deserialization.cpp

@@ -4678,6 +4678,13 @@ void ModuleFile::loadAllMembers(Decl *container, uint64_t contextData) {
   }
 }
 
+bool ModuleFile::loadNamedMembers(const Decl *D, DeclName N,
+                                  uint64_t contextData,
+                                  TinyPtrVector<ValueDecl *> &Members) {
+  // Not presently supported.
+  return true;
+}
+
 void
 ModuleFile::loadAllConformances(const Decl *D, uint64_t contextData,
                           SmallVectorImpl<ProtocolConformance*> &conformances) {