[Serialization] Implement serialization/deserialization for the typeEraser

attribute.

Author: hborla

include/swift/AST/Attr.def

@@ -520,7 +520,7 @@ SIMPLE_DECL_ATTR(_inheritsConvenienceInitializers,
   93)
 
 DECL_ATTR(_typeEraser, TypeEraser,
-  OnProtocol | UserInaccessible | NotSerialized |
+  OnProtocol | UserInaccessible |
   ABIStableToAdd | ABIBreakingToRemove | APIStableToAdd | APIBreakingToRemove,
   94)
 

lib/Serialization/Deserialization.cpp

@@ -4208,6 +4208,19 @@ llvm::Error DeclDeserializer::deserializeDeclAttributes() {
         break;
       }
 
+      case decls_block::TypeEraser_DECL_ATTR: {
+        bool isImplicit;
+        TypeID typeEraserID;
+        serialization::decls_block::TypeEraserDeclAttrLayout::readRecord(
+            scratch, isImplicit, typeEraserID);
+
+        auto typeEraser = MF.getType(typeEraserID);
+        assert(!isImplicit);
+        Attr = new (ctx) TypeEraserAttr(SourceLoc(), SourceRange(),
+                                        TypeLoc::withoutLoc(typeEraser));
+        break;
+      }
+
       case decls_block::Custom_DECL_ATTR: {
         bool isImplicit;
         TypeID typeID;

lib/Serialization/Serialization.cpp

@@ -2173,7 +2173,6 @@ class Serializer::DeclSerializer : public DeclVisitor<DeclSerializer> {
     case DAK_RestatedObjCConformance:
     case DAK_ClangImporterSynthesizedType:
     case DAK_PrivateImport:
-    case DAK_TypeEraser:
       llvm_unreachable("cannot serialize attribute");
 
     case DAK_Count:
@@ -2364,6 +2363,16 @@ class Serializer::DeclSerializer : public DeclVisitor<DeclSerializer> {
       return;
     }
 
+    case DAK_TypeEraser: {
+      auto abbrCode = S.DeclTypeAbbrCodes[TypeEraserDeclAttrLayout::Code];
+      auto attr = cast<TypeEraserAttr>(DA);
+      auto typeEraser = attr->getTypeEraserLoc().getType();
+      TypeEraserDeclAttrLayout::emitRecord(S.Out, S.ScratchRecord, abbrCode,
+                                           attr->isImplicit(),
+                                           S.addTypeRef(typeEraser));
+      return;
+    }
+
     case DAK_Custom: {
       auto abbrCode = S.DeclTypeAbbrCodes[CustomDeclAttrLayout::Code];
       auto theAttr = cast<CustomAttr>(DA);