Serialization: Don't fail out of loadNamedMembers()

This cleanup exposed a problem with deserialization recovery and
property wrappers. If deserializing a property backed by a wrapper
failed, the lazy member lookup would fail, but subsequently a
loadAllMembers() call would still load the property.

This behavior is actually incorrect, because silently dropping a
stored property of a @Frozen struct can result in miscompiles.
I've filed rdar://59403542 and rdar://59403617 to track fixing this.

In the meantime, I've tweaked the logic a bit to preserve the old
behavior.

Author: slavapestov

lib/Serialization/Deserialization.cpp

@@ -2831,14 +2831,10 @@ class DeclDeserializer {
     if (numBackingProperties > 0) {
       auto backingDecl = MF.getDeclChecked(backingPropertyIDs[0]);
       if (!backingDecl) {
-        if (numBackingProperties > 1 &&
-            backingDecl.errorIsA<XRefNonLoadedModuleError>()) {
-            // A property wrapper defined behind an implementation-only import
-            // is safe to drop when it can't be deserialized.
-            // rdar://problem/56599179
-            consumeError(backingDecl.takeError());
-        } else
-          return backingDecl.takeError();
+        // FIXME: This is actually wrong. We can't just drop stored properties
+        // willy-nilly if the struct is @frozen.
+        consumeError(backingDecl.takeError());
+        return var;
       }
 
       VarDecl *backingVar = cast<VarDecl>(backingDecl.get());

lib/Serialization/ModuleFile.cpp

@@ -2399,7 +2399,7 @@ ModuleFile::loadNamedMembers(const IterableDeclContext *IDC, DeclBaseName N,
         fatalIfUnexpected(DeclMemberTablesCursor.advance());
     if (entry.Kind != llvm::BitstreamEntry::Record) {
       fatal();
-      return None;
+      return results;
     }
     SmallVector<uint64_t, 64> scratch;
     StringRef blobData;
@@ -2424,10 +2424,6 @@ ModuleFile::loadNamedMembers(const IterableDeclContext *IDC, DeclBaseName N,
         if (!getContext().LangOpts.EnableDeserializationRecovery)
           fatal(mem.takeError());
         consumeError(mem.takeError());
-
-        // Treat this as a cache-miss to the caller and let them attempt
-        // to refill through the normal loadAllMembers() path.
-        return None;
       }
     }
   }