cue: use unwrapJSONError in the entrypoint API only

It's already called from Value.MarshalJSON, the exported API,
so there's no need to call it from the internal APIs it calls too.
Any errors that structValue.marshalJSON or marshalList return
are already unwrapped by Value.MarshalJSON before returning.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: I01ca43692b9d1c315c501df01240d42a1c8b5324
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1201806
Reviewed-by: Roger Peppe <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>

Author: mvdan

cue/types.go

@@ -143,20 +143,20 @@ func (o *hiddenStructValue) Lookup(key string) Value {
 
 // MarshalJSON returns a valid JSON encoding or reports an error if any of the
 // fields is invalid.
-func (o *structValue) marshalJSON() (b []byte, err errors.Error) {
+func (o *structValue) marshalJSON() (b []byte, err error) {
 	b = append(b, '{')
 	n := o.Len()
 	for i := range n {
 		k, v := o.At(i)
 		s, err := internaljson.Marshal(k)
 		if err != nil {
-			return nil, unwrapJSONError(err)
+			return nil, err
 		}
 		b = append(b, s...)
 		b = append(b, ':')
 		bb, err := internaljson.Marshal(v)
 		if err != nil {
-			return nil, unwrapJSONError(err)
+			return nil, err
 		}
 		b = append(b, bb...)
 		if i < n-1 {
@@ -294,13 +294,13 @@ func (i *hiddenIterator) IsDefinition() bool {
 
 // marshalJSON iterates over the list and generates JSON output. HasNext
 // will return false after this operation.
-func marshalList(l *Iterator) (b []byte, err errors.Error) {
+func marshalList(l *Iterator) (b []byte, err error) {
 	b = append(b, '[')
 	if l.Next() {
 		for i := 0; ; i++ {
 			x, err := internaljson.Marshal(l.Value())
 			if err != nil {
-				return nil, unwrapJSONError(err)
+				return nil, err
 			}
 			b = append(b, x...)
 			if !l.Next() {