[DeclChecker] Don't try to derive conformances for invalid enums

If one of the cases is invalid, let's mark parent enum as invalid
as well, and avoid trying to derive any conformances related to it.

Resolves: rdar://problem/36989792
(cherry picked from commit 38e305c)

Author: xedin

lib/Sema/TypeCheckDecl.cpp

@@ -4518,6 +4518,7 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
       {
         // Check for duplicate enum members.
         llvm::DenseMap<Identifier, EnumElementDecl *> Elements;
+        bool hasErrors = false;
         for (auto *EED : ED->getAllElements()) {
           auto Res = Elements.insert({ EED->getName(), EED });
           if (!Res.second) {
@@ -4530,8 +4531,14 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
             TC.diagnose(EED->getLoc(), diag::duplicate_enum_element);
             TC.diagnose(PreviousEED->getLoc(),
                         diag::previous_decldef, true, EED->getName());
+            hasErrors = true;
           }
         }
+
+        if (hasErrors) {
+          ED->setInterfaceType(ErrorType::get(TC.Context));
+          ED->setInvalid();
+        }
       }
     }
 

lib/Sema/TypeCheckProtocol.cpp

@@ -4655,6 +4655,8 @@ ValueDecl *TypeChecker::deriveProtocolRequirement(DeclContext *DC,
     return nullptr;
 
   auto Decl = DC->getInnermostDeclarationDeclContext();
+  if (Decl->isInvalid())
+    return nullptr;
 
   switch (*knownKind) {
   case KnownProtocolKind::RawRepresentable:

validation-test/compiler_crashers_2_fixed/0141-rdar36989792.swift

@@ -0,0 +1,6 @@
+// RUN: not %target-swift-frontend %s -typecheck
+
+enum E : Equatable {
+    case c(Int)
+    case c(String)
+}