[serialization] Add support for TupleTypes.

These are implementing using trailing TUPLE_TYPE_ELT records after the
initial TUPLE_TYPE record. This is the next step towards function decls.

Element initializers are silently ignored for now.

Also, do serialize a record for IdentifierTypes, even though we're not
including the components yet, so that we don't serialize the underlying
type more than once.

Swift SVN r5683

lib/Serialization/ModuleFile.cpp

@@ -13,6 +13,7 @@
 #include "ModuleFile.h"
 #include "ModuleFormat.h"
 #include "swift/AST/AST.h"
+#include "swift/Serialization/BCReadingExtras.h"
 #include "llvm/Support/MemoryBuffer.h"
 
 using namespace swift;
@@ -370,6 +371,46 @@ Type ModuleFile::getType(TypeID TID) {
     break;
   }
 
+  case decls_block::TUPLE_TYPE: {
+    // The tuple record itself is empty. Read all trailing elements.
+    SmallVector<TupleTypeElt, 8> elements;
+    while (true) {
+      auto entry = DeclTypeCursor.advance();
+      if (entry.Kind != llvm::BitstreamEntry::Record)
+        break;
+
+      scratch.clear();
+      unsigned recordID = DeclTypeCursor.readRecord(entry.ID, scratch,
+                                                    &blobData);
+      if (recordID != decls_block::TUPLE_TYPE_ELT)
+        break;
+
+      IdentifierID nameID;
+      TypeID typeID;
+      TypeID varargBaseID;
+      decls_block::TupleTypeEltLayout::readRecord(scratch, nameID, typeID,
+                                                  varargBaseID);
+
+      {
+        BCOffsetRAII restoreOffset(DeclTypeCursor);
+        elements.push_back({getType(typeID), getIdentifier(nameID),
+                            /*initializer=*/nullptr, getType(varargBaseID)});
+      }
+    }
+
+    typeOrOffset = TupleType::get(elements, ModuleContext->Ctx);
+    break;
+  }
+
+  case decls_block::IDENTIFIER_TYPE: {
+    TypeID mappedID;
+    decls_block::IdentifierTypeLayout::readRecord(scratch, mappedID);
+    // FIXME: Actually recreate the IdentifierType instead of just aliasing the
+    // underlying mapped type.
+    typeOrOffset = getType(mappedID);
+    break;
+  }
+
   default:
     // We don't know how to deserialize this kind of type.
     error();