internal/core/adt: clean up "withinLet"

Now we have a different mechanism for
forcing evaluation of a field, we no longer
need to special-case let values introduced
in  https://cuelang.org/cl/1211827

We remove this mechanism.

Issue #3763

Signed-off-by: Marcel van Lohuizen <[email protected]>
Change-Id: I76d020dda5a6e80d8191f96fdad270829d534d6a
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1211977
TryBot-Result: CUEcueckoo <[email protected]>
Reviewed-by: Matthew Sackman <[email protected]>

Author: mpvl

internal/core/adt/composite.go

@@ -226,9 +226,6 @@ type Vertex struct {
 	// the for source of comprehensions and let fields or let clauses.
 	anonymous bool
 
-	// withinLet indicate that this vertex is a let value.
-	withinLet bool
-
 	// hasPendingArc is set if this Vertex has a void arc (e.g. for comprehensions)
 	hasPendingArc bool
 
@@ -1359,7 +1356,6 @@ func (v *Vertex) GetArc(c *OpContext, f Feature, t ArcType) (arc *Vertex, isNew
 		ArcType:   t,
 		nonRooted: v.IsDynamic || v.Label.IsLet() || v.nonRooted,
 		anonymous: v.anonymous || v.Label.IsLet(),
-		withinLet: v.withinLet || v.Label.IsLet(),
 	}
 	v.Arcs = append(v.Arcs, arc)
 	if t == ArcPending {

internal/core/adt/cycle.go

@@ -700,7 +700,7 @@ func (n *nodeContext) detectCycleV3(arc *Vertex, env *Environment, x Resolver, c
 
 			return n.markCyclicPathV3(arc, env, x, ci)
 		}
-		if equalDeref(r.Node, n.node) && r.Ref == x && (arc.nonRooted || arc.withinLet) {
+		if equalDeref(r.Node, n.node) && r.Ref == x && arc.nonRooted {
 			return n.markCyclicPathV3(arc, env, x, ci)
 		}
 	}

internal/core/adt/fields.go

@@ -169,7 +169,6 @@ func (n *nodeContext) getArc(f Feature, mode ArcType) (arc *Vertex, isNew bool)
 		ArcType:   mode,
 		nonRooted: v.IsDynamic || v.nonRooted,
 		anonymous: v.anonymous || v.Label.IsLet(),
-		withinLet: v.withinLet || v.Label.IsLet(),
 	}
 	if n.scheduler.frozen&fieldSetKnown != 0 {
 		b := n.ctx.NewErrf("adding field %v not allowed as field set was already referenced", f)

internal/core/adt/unify.go

@@ -868,8 +868,7 @@ func (v *Vertex) lookup(c *OpContext, pos token.Pos, f Feature, flags combinedFl
 			// not trigger the usual unblocking. Force unblocking may cause
 			// some values to be remain unevaluated.
 			switch {
-			case arc.withinLet,
-				needs == arcTypeKnown|fieldSetKnown:
+			case needs == arcTypeKnown|fieldSetKnown:
 				arc.unify(c, needs, finalize, false)
 			default:
 				// Now we can't finalize, at least try to get as far as we