[AST/Sema] Don't crash when referencing enum case in where-clause

include/swift/AST/Decl.h

@@ -5270,7 +5270,9 @@ class EnumElementDecl : public ValueDecl {
         static_cast<unsigned>(ElementRecursiveness::NotRecursive);
   }
 
-  void computeType();
+  /// \returns false if there was an error during the computation rendering the
+  /// EnumElementDecl invalid, true otherwise.
+  bool computeType();
 
   bool hasArgumentType() const { return !ArgumentType.getType().isNull(); }
   Type getArgumentType() const { return ArgumentType.getType(); }

lib/AST/Decl.cpp

@@ -4309,10 +4309,15 @@ SourceRange EnumElementDecl::getSourceRange() const {
   return {getStartLoc(), getNameLoc()};
 }
 
-void EnumElementDecl::computeType() {
+bool EnumElementDecl::computeType() {
   EnumDecl *ED = getParentEnum();
-
   Type resultTy = ED->getDeclaredTypeInContext();
+
+  if (resultTy->is<ErrorType>()) {
+    setType(resultTy);
+    return false;
+  }
+
   Type argTy = MetatypeType::get(resultTy);
 
   // The type of the enum element is either (T) -> T or (T) -> ArgType -> T.
@@ -4326,6 +4331,7 @@ void EnumElementDecl::computeType() {
     resultTy = FunctionType::get(argTy, resultTy);
 
   setType(resultTy);
+  return true;
 }
 
 Type EnumElementDecl::getArgumentInterfaceType() const {

lib/Sema/TypeCheckDecl.cpp

@@ -5543,11 +5543,14 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
       EED->setRecursiveness(ElementRecursiveness::NotRecursive);
     }
 
-    // Now that we have an argument type we can set the element's declared
-    // type.
-    if (!EED->hasType())
-      EED->computeType();
-    EED->setIsBeingTypeChecked(false);
+    {
+      defer { EED->setIsBeingTypeChecked(false); };
+
+      // Now that we have an argument type we can set the element's declared
+      // type.
+      if (!EED->hasType() && !EED->computeType())
+        return;
+    }
 
     // Test for type parameters, as opposed to a generic decl context, in
     // case the enclosing enum type was illegally declared inside of a generic

test/Generics/generic_types.swift

@@ -334,3 +334,5 @@ struct UnsolvableInheritance1<T : T.A> {}
 struct UnsolvableInheritance2<T : U.A, U : T.A> {}
 // expected-error@-1 {{inheritance from non-protocol, non-class type 'U.A'}}
 // expected-error@-2 {{inheritance from non-protocol, non-class type 'T.A'}}
+
+enum X7<T where X7.X : G> { case X } // expected-error{{'X' is not a member type of 'X7<T>'}}

validation-test/compiler_crashers/28224-swift-genericfunctiontype-get.swift → validation-test/compiler_crashers_fixed/28224-swift-genericfunctiontype-get.swift

@@ -5,6 +5,6 @@
 // See http://swift.org/LICENSE.txt for license information
 // See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 
-// RUN: not --crash %target-swift-frontend %s -parse
+// RUN: not %target-swift-frontend %s -parse
 // REQUIRES: asserts
 {enum S<T where S.c:A{case c