Summon the eldritch horror "EagerDeserializationDecls" from the bowels of history.

Adding explicit constructors to Clang-imported structs in the previous commits exposes a latent phase ordering issue between the Clang importer and SIL deserialization. Deserializing the standard library SIL ends up pulling in additional Clang decls which never get type-checked before we attempt to emit their code. Work around this by bringing back the "EagerDeserializedDecls" block in the serialization format, and adding any cross-referenced decls that get referenced in SILSerializeAll mode to it, so that we ensure they're available before SILGen. We also have to type-check external decls after doing so, since when only importing a module, we wouldn't do any type-checking at all otherwise.

Swift SVN r23728

lib/Serialization/ModuleFile.cpp

@@ -323,6 +323,8 @@ ModuleFile::readObjCMethodTable(ArrayRef<uint64_t> fields, StringRef blobData) {
                                              base + sizeof(uint32_t), base));
 }
 
+
+
 bool ModuleFile::readIndexBlock(llvm::BitstreamCursor &cursor) {
   cursor.EnterSubBlock(INDEX_BLOCK_ID);
 
@@ -378,6 +380,11 @@ bool ModuleFile::readIndexBlock(llvm::BitstreamCursor &cursor) {
         break;
       case index_block::OBJC_METHODS:
         ObjCMethods = readObjCMethodTable(scratch, blobData);
+        break;
+      case index_block::FORCE_DESERIALIZATION:
+        std::copy(scratch.begin(), scratch.end(),
+                  std::back_inserter(EagerDeserializationDecls));
+        
         break;
       default:
         // Unknown index kind, which this version of the compiler won't use.
@@ -887,6 +894,13 @@ bool ModuleFile::associateWithFileContext(FileUnit *file, SourceLoc diagLoc) {
   if (Bits.HasUnderlyingModule)
     (void)getModule(FileContext->getParentModule()->Name);
 
+  // Process decls we know we want to eagerly deserialize.
+  if (!EagerDeserializationDecls.empty()) {
+    for (DeclID DID : EagerDeserializationDecls)
+      getDecl(DID);
+    typeCheckExternalDefinitions(*FileContext);
+  }
+
   return getStatus() == ModuleStatus::Valid;
 }