[Serialization] Look for cross-ref errors inside type errors (swiftlang#33271)

In swiftlang#30614, we started consuming XRefNonLoadedModuleErrors while loading
conformances, since a conformance to a type we cannot load usually
indicates we're trying to load a protocol that was declared in an
@_implementationOnly imported module.

We should also consume TypeErrors that we see where the underlying reason
is an XRefNonLoadedModuleError, since they're likely indicators of the
same thing.

Author: Harlan Haskins

lib/Serialization/Deserialization.cpp

@@ -5951,6 +5951,33 @@ void ModuleFile::loadAllMembers(Decl *container, uint64_t contextData) {
   }
 }
 
+static llvm::Error consumeErrorIfXRefNonLoadedModule(llvm::Error &&error) {
+    // Missing module errors are most likely caused by an
+    // implementation-only import hiding types and decls.
+    // rdar://problem/60291019
+    if (error.isA<XRefNonLoadedModuleError>()) {
+      consumeError(std::move(error));
+      return llvm::Error::success();
+    }
+
+    // Some of these errors may manifest as a TypeError with an
+    // XRefNonLoadedModuleError underneath. Catch those as well.
+    // rdar://66491720
+    if (error.isA<TypeError>()) {
+      auto errorInfo = takeErrorInfo(std::move(error));
+      auto *TE = static_cast<TypeError*>(errorInfo.get());
+
+      if (TE->underlyingReasonIsA<XRefNonLoadedModuleError>()) {
+        consumeError(std::move(errorInfo));
+        return llvm::Error::success();
+      }
+
+      return std::move(errorInfo);
+    }
+
+    return std::move(error);
+}
+
 void
 ModuleFile::loadAllConformances(const Decl *D, uint64_t contextData,
                           SmallVectorImpl<ProtocolConformance*> &conformances) {
@@ -5968,15 +5995,11 @@ ModuleFile::loadAllConformances(const Decl *D, uint64_t contextData,
     auto conformance = readConformanceChecked(DeclTypeCursor);
 
     if (!conformance) {
-      // Missing module errors are most likely caused by an
-      // implementation-only import hiding types and decls.
-      // rdar://problem/60291019
-      if (conformance.errorIsA<XRefNonLoadedModuleError>()) {
-        consumeError(conformance.takeError());
-        return;
-      }
-      else
-        fatal(conformance.takeError());
+      auto unconsumedError =
+        consumeErrorIfXRefNonLoadedModule(conformance.takeError());
+      if (unconsumedError)
+        fatal(std::move(unconsumedError));
+      return;
     }
 
     if (conformance.get().isConcrete())

lib/Serialization/DeserializationErrors.h

@@ -352,6 +352,13 @@ class TypeError : public llvm::ErrorInfo<TypeError, DeclDeserializationError> {
     this->numVTableEntries = numVTableEntries;
   }
 
+  template <typename UnderlyingErrorT>
+  bool underlyingReasonIsA() const {
+    if (!underlyingReason)
+      return false;
+    return underlyingReason->isA<UnderlyingErrorT>();
+  }
+
   void log(raw_ostream &OS) const override {
     OS << "could not deserialize type for '" << name << "'";
     if (underlyingReason) {

test/Serialization/Recovery/implementation-only-missing.swift

@@ -81,11 +81,24 @@ struct StructWithOverride: HiddenProtocolWithOverride {
   func hiddenOverride() {}
 }
 
+internal protocol RefinesHiddenProtocol: HiddenProtocol {
+
+}
+
+public struct PublicStructConformsToHiddenProtocol: RefinesHiddenProtocol {
+  public typealias Value = Int
+
+  public init() { }
+}
+
 #elseif CLIENT_APP
 
 import public_lib
 
 var s = PublicStruct()
 print(s.nonWrappedVar)
 
+var p = PublicStructConformsToHiddenProtocol()
+print(p)
+
 #endif