internal/core/adt: prevent state inversion

Prevent evaluting with a lower state than requested.

Also make ForClause request Finalized: with the
upcoming comprehension changes this is needed to
elminate void arcs.

Change-Id: I95bf5db80265dd7a12e9015c13429c9ff505a97b
Signed-off-by: Marcel van Lohuizen <mpvl@golang.org>
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/533224
Unity-Result: CUEcueckoo <cueckoo@cuelang.org>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Reviewed-by: Marcel van Lohuizen <mpvl@gmail.com>

Author: mpvl

cue/testdata/builtins/incomplete.txtar

@@ -116,26 +116,26 @@ Result:
   list1: (struct){
     Out1: (#list){
       0: (_|_){
-        // [cycle] cycle error:
-        //     ./in.cue:17:23
+        // [incomplete] list1._Sub: undefined field: b:
+        //     ./in.cue:20:13
       }
     }
     Out2: (#list){
       0: (_|_){
-        // [cycle] cycle error:
-        //     ./in.cue:17:23
+        // [incomplete] list1._Sub: undefined field: b:
+        //     ./in.cue:20:13
       }
     }
     Out3: (#list){
       0: (_|_){
-        // [cycle] cycle error:
-        //     ./in.cue:17:23
+        // [incomplete] list1._Sub: undefined field: b:
+        //     ./in.cue:20:13
       }
     }
     Top: (#list){
       0: (_|_){
-        // [cycle] cycle error:
-        //     ./in.cue:17:23
+        // [incomplete] list1._Sub: undefined field: b:
+        //     ./in.cue:20:13
       }
     }
     _Sub: (_|_){
@@ -147,20 +147,20 @@ Result:
   }
   list2: (struct){
     Out1: (_|_){
-      // [cycle] cycle error:
-      //     ./in.cue:31:21
+      // [incomplete] list2.#Sub: undefined field: b:
+      //     ./in.cue:34:13
     }
     Out2: (_|_){
-      // [cycle] cycle error:
-      //     ./in.cue:31:21
+      // [incomplete] list2.#Sub: undefined field: b:
+      //     ./in.cue:34:13
     }
     Out3: (_|_){
-      // [cycle] cycle error:
-      //     ./in.cue:31:21
+      // [incomplete] list2.#Sub: undefined field: b:
+      //     ./in.cue:34:13
     }
     _Top: (_|_){
-      // [cycle] cycle error:
-      //     ./in.cue:31:21
+      // [incomplete] list2.#Sub: undefined field: b:
+      //     ./in.cue:34:13
     }
     #Sub: (_|_){
       // [incomplete] list2.#Sub: undefined field: b:

cue/testdata/eval/closedness.txtar

@@ -52,6 +52,7 @@ a.q: field not allowed: e:
     ./in.cue:11:4
     ./in.cue:15:9
 issue852.a: field not allowed: Foo:
+    ./in.cue:30:15
     ./in.cue:22:7
     ./in.cue:26:6
     ./in.cue:28:6
@@ -87,21 +88,23 @@ Result:
     }
   }
   issue852: (_|_){
-    // [eval]
+    // [eval] issue852.a: field not allowed: Foo:
+    //     ./in.cue:30:15
+    //     ./in.cue:22:7
+    //     ./in.cue:26:6
+    //     ./in.cue:28:6
     #A: (#struct){
     }
     a: (_|_){
       // [eval]
       Foo: (_|_){
         // [eval] issue852.a: field not allowed: Foo:
+        //     ./in.cue:30:15
         //     ./in.cue:22:7
         //     ./in.cue:26:6
         //     ./in.cue:28:6
       }
     }
-    b: (struct){
-      Foo: (string){ "foo" }
-    }
   }
   dynamic: (struct){
     #D: (#struct){

internal/core/adt/context.go

@@ -695,8 +695,13 @@ func (c *OpContext) unifyNode(v Expr, state VertexStatus) (result Value) {
 		}
 
 		if v.isUndefined() {
+			// Keep a minimum state of AllArcs.
+			state := state
+			if state < AllArcs {
+				state = AllArcs
+			}
 			// Use node itself to allow for cycle detection.
-			c.Unify(v, AllArcs)
+			c.Unify(v, state)
 		}
 
 		return v

internal/core/adt/expr.go

@@ -1637,7 +1637,7 @@ func (x *ForClause) Source() ast.Node {
 }
 
 func (x *ForClause) yield(c *OpContext, f YieldFunc) {
-	n := c.node(x, x.Src, true, AllArcs)
+	n := c.node(x, x.Src, true, Finalized)
 	for _, a := range n.Arcs {
 		if !a.Label.IsRegular() {
 			continue