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/Serialization.h

@@ -49,6 +49,8 @@ class Serializer {
   const SourceFile *SF = nullptr;
 
 public:
+  const SerializationOptions &Options;
+
   /// Stores a declaration or a type to be written to the AST file.
   ///
   /// Convenience wrapper around a PointerUnion.
@@ -142,8 +144,8 @@ private:
   /// IdentifierID.
   std::vector<CharOffset> IdentifierOffsets;
 
-  /// The decls that adopt compiler-known protocols.
-  SmallVector<DeclID, 2> KnownProtocolAdopters[NumKnownProtocols];
+  /// Decls to be eagerly deserialized.
+  SmallVector<DeclID, 2> EagerDeserializationDecls;
 
   /// The last assigned DeclID for decls from this module.
   DeclID LastDeclID = 0;
@@ -264,7 +266,8 @@ private:
   void writeToStream(raw_ostream &os);
 
   template <size_t N>
-  Serializer(const unsigned char (&signature)[N], ModuleOrSourceFile DC);
+  Serializer(const unsigned char (&signature)[N], ModuleOrSourceFile DC,
+             const SerializationOptions &Options);
 
 public:
   /// Serialize a module to the given stream.