Fixed CHECK failures on certain usage of incomplete enums.

src/cc65/datatype.c

@@ -686,7 +686,10 @@ const Type* GetUnderlyingType (const Type* Type)
             Internal ("Enum tag type error in GetUnderlyingTypeCode");
         }
 
-        return ((SymEntry*)Type->A.P)->V.E.Type;
+        /* If incomplete enum type is used, just return its raw type */
+        if (((SymEntry*)Type->A.P)->V.E.Type != 0) {
+            return ((SymEntry*)Type->A.P)->V.E.Type;
+        }
     }
 
     return Type;
@@ -1246,9 +1249,14 @@ Type* IntPromotion (Type* T)
         ** to unsigned int.
         */
         return IsSignUnsigned (T) ? type_uint : type_int;
-    } else {
+    } else if (!IsIncompleteESUType (T)) {
-        /* Otherwise, the type is not smaller than int, so leave it alone. */
+        /* The type is a complete type not smaller than int, so leave it alone. */
         return T;
+    } else {
+        /* Otherwise, this is an incomplete enum, and there is expceted to be an error already.
+        ** Assume int to avoid further errors.
+        */
+        return type_int;
     }
 }
 

src/cc65/loadexpr.c

@@ -142,6 +142,10 @@ void LoadExpr (unsigned Flags, struct ExprDesc* Expr)
                 BitFieldFullWidthFlags |= CF_UNSIGNED;
             }
         } else if ((Flags & CF_TYPEMASK) == 0) {
+            /* If Expr is an incomplete ESY type, bail out */
+            if (IsIncompleteESUType (Expr->Type)) {
+                return;
+            }
             Flags |= TypeOf (Expr->Type);
         }