Serialization: Align conformance recovery logic across modes

Always give up early when attempting to deserialize a protocol
conformance broken by a context change. Don't attempt to replace missing
members of the conformance signature with invalid one, just mark the
whole protocol conformance as invalid.

The previous recovery logic, only for SourceKit mode and LLDB, was
inserting invalid conformances in the signature instead of dropping the
whole protocol conformance. It lead to failures later in the same
`finishNormalConformance` when accessing the invalid conformances.

rdar://98925842

Author: xymus

lib/Serialization/Deserialization.cpp

@@ -1005,13 +1005,13 @@ ProtocolConformanceDeserializer::readNormalProtocolConformanceXRef(
   auto error = llvm::make_error<ConformanceXRefError>(
                  nominal->getName(), proto->getName(), module);
 
-  if (!MF.enableExtendedDeserializationRecovery()) {
-    error = llvm::handleErrors(std::move(error),
-      [&](const ConformanceXRefError &error) -> llvm::Error {
-        error.diagnose(&MF);
-        return llvm::make_error<ConformanceXRefError>(std::move(error));
-      });
-  }
+  // Diagnose the root error here.
+  error = llvm::handleErrors(std::move(error),
+    [&](const ConformanceXRefError &error) -> llvm::Error {
+      error.diagnose(&MF);
+      return llvm::make_error<ConformanceXRefError>(std::move(error));
+    });
+
   return error;
 }
 
@@ -8868,23 +8868,27 @@ void ModuleFile::finishNormalConformance(NormalProtocolConformance *conformance,
     if (maybeConformance) {
       reqConformances.push_back(maybeConformance.get());
     } else if (getContext().LangOpts.EnableDeserializationRecovery) {
-      llvm::Error error = maybeConformance.takeError();
-      if (error.isA<ConformanceXRefError>() &&
-          !enableExtendedDeserializationRecovery()) {
+      // If a conformance is missing, mark the whole protocol conformance
+      // as invalid. Something is broken with the context.
+      conformance->setInvalid();
 
+      llvm::Error error = maybeConformance.takeError();
+      if (error.isA<ConformanceXRefError>()) {
+        // The error was printed along with creating the ConformanceXRefError.
+        // Print the note here explaining the side effect.
         std::string typeStr = conformance->getType()->getString();
         auto &diags = getContext().Diags;
         diags.diagnose(getSourceLoc(),
                        diag::modularization_issue_conformance_xref_note,
                        typeStr, proto->getName());
 
         consumeError(std::move(error));
-        conformance->setInvalid();
         return;
       }
 
+      // Leave it up to the centralized service to report other errors.
       diagnoseAndConsumeError(std::move(error));
-      reqConformances.push_back(ProtocolConformanceRef::forInvalid());
+      return;
     } else {
       fatal(maybeConformance.takeError());
     }