internal/core/adt: fix closedness bug

It is incorrect to assume that if a close builtin is used within
a definition, it no longer needs to be marked as closed.
For instance, locally, it may be unified with another field
that is illegal.

Signed-off-by: Marcel van Lohuizen <[email protected]>
Change-Id: I6d05b551593eda115a86d0309fd1accd2ed101b0
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1172013
Unity-Result: CUE porcuepine <[email protected]>
Reviewed-by: Daniel Martí <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>

Author: mpvl

cue/testdata/comprehensions/issue293.txtar

@@ -28,7 +28,7 @@ t: p: "foo"
 -- variant1.cue --
 #V1: {
 	x: close({ f1: int })
-	x: f2: 2 // TODO: fail
+	x: f2: 2
 }
 -- out/eval/stats --
 Leaks:  3
@@ -42,6 +42,9 @@ Conjuncts:    33
 Disjuncts:    20
 -- out/eval --
 Errors:
+#V1.x.f2: field not allowed:
+    ./variant1.cue:2:11
+    ./variant1.cue:3:5
 z.x.f2: field not allowed:
     ./in.cue:2:2
     ./in.cue:5:12
@@ -76,10 +79,16 @@ Result:
   #C: (#struct){
     p: (_){ _ }
   }
-  #V1: (#struct){
-    x: (#struct){
+  #V1: (_|_){
+    // [eval]
+    x: (_|_){
+      // [eval]
       f1: (int){ int }
-      f2: (int){ 2 }
+      f2: (_|_){
+        // [eval] #V1.x.f2: field not allowed:
+        //     ./variant1.cue:2:11
+        //     ./variant1.cue:3:5
+      }
     }
   }
 }

internal/core/compile/builtin.go

@@ -86,7 +86,7 @@ var closeBuiltin = &adt.Builtin{
 		if !ok {
 			return c.NewErrf("struct argument must be concrete")
 		}
-		if m, ok := s.BaseValue.(*adt.StructMarker); ok && m.NeedClose || s.Closed {
+		if m, ok := s.BaseValue.(*adt.StructMarker); ok && m.NeedClose {
 			return s
 		}
 		v := s.Clone()