upon cycle detection, say it's noncopyable

Author: kavon

lib/AST/Decl.cpp

@@ -3398,9 +3398,13 @@ bool ValueDecl::isFinal() const {
 }
 
 bool ValueDecl::isMoveOnly() const {
+  // Default answer if a cycle is detected is to say it is noncopyable.
+  // My reasoning is that permitting copying when the user _might_ have intended
+  // for it to be noncopyable is unacceptable as it can lead to silent problems.
+  // At least they'll get unexpected errors if they were expecting to copy!
   return evaluateOrDefault(getASTContext().evaluator,
                            IsMoveOnlyRequest{const_cast<ValueDecl *>(this)},
-                           getAttrs().hasAttribute<MoveOnlyAttr>());
+                           /*noncopyable=*/true);
 }
 
 bool TypeDecl::isSuppressingConformance(KnownProtocolKind kp) const {