internal/core/adt: check right Vertex for single-level close

The condition checked the existing Vertex,
instead of the incoming one. Strangely
enough, this had no effect. This is probably
because n.node was already updated for the
fact that v is closed. To make the code more
robust to future changes, though, we check
the value of v, not n.node.

Also updates a comment.

Signed-off-by: Marcel van Lohuizen <[email protected]>
Change-Id: I8129b80632c854ec46c6d54ece022b092542fcf3
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1211934
TryBot-Result: CUEcueckoo <[email protected]>
Reviewed-by: Daniel Martí <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>

Author: mpvl

Diff for: internal/core/adt/typocheck.go

@@ -262,7 +262,7 @@ func (n *nodeContext) addResolver(v *Vertex, id CloseInfo, forceIgnore bool) Clo
 		return id
 	}
 
-	isClosed := id.FromDef || n.node.ClosedNonRecursive
+	isClosed := id.FromDef || v.ClosedNonRecursive
 
 	if isClosed {
 		for i, x := range n.reqDefIDs {
@@ -623,7 +623,7 @@ outer:
 				} else {
 					temp = append(temp, buf...)
 				}
-				buf = buf[:0] // TODO: perf use OpContext buffer.
+				buf = buf[:0] // TODO(perf): use OpContext buffer.
 			}
 		}