internal/core/adt: add methods for concreteness

This is the first step to make marker value a different
type as to let the compiler prevent them from
being passed around as values.

Issue #598

Change-Id: Iaf58635bd2ca4591e6ce4589f237076ff8359ede
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/7764
Reviewed-by: Marcel van Lohuizen <[email protected]>
Reviewed-by: CUE cueckoo <[email protected]>

Author: mpvl

cue/context.go

@@ -76,12 +76,7 @@ func (v Value) eval(ctx *context) adt.Value {
 		panic("undefined value")
 	}
 	x := ctx.manifest(v.v)
-	switch x.Kind() {
-	case adt.StructKind, adt.ListKind:
-		return x
-	default:
-		return x.Value
-	}
+	return x.ActualValue()
 }
 
 // func (v Value) evalFull(u value) (Value, adt.Value) {

cue/load/config.go

@@ -536,12 +536,12 @@ func (c Config) complete() (cfg *Config, err error) {
 		v.Finalize(ctx)
 		prefix := v.Lookup(ctx.StringLabel("module"))
 		if prefix != nil {
-			name := ctx.StringValue(prefix.Value)
+			name := ctx.StringValue(prefix.ActualValue())
 			if err := ctx.Err(); err != nil {
 				return &c, err.Err
 			}
 			pos := token.NoPos
-			src := prefix.Value.Source()
+			src := prefix.ActualValue().Source()
 			if src != nil {
 				pos = src.Pos()
 			}

cue/types.go

@@ -844,7 +844,7 @@ func (v Value) Kind() Kind {
 		return BottomKind
 	}
 	c := v.v.Value
-	if !adt.IsConcrete(c) {
+	if !v.v.IsConcrete() {
 		return BottomKind
 	}
 	if v.IncompleteKind() == adt.ListKind && !v.IsClosed() {
@@ -2161,25 +2161,15 @@ func (v Value) Expr() (Op, []Value) {
 	var env *adt.Environment
 
 	if v.v.IsData() {
-		switch x := v.v.Value.(type) {
-		case *adt.ListMarker, *adt.StructMarker:
-			expr = v.v
-		default:
-			expr = x
-		}
+		expr = v.v.ActualValue()
 
 	} else {
 		switch len(v.v.Conjuncts) {
 		case 0:
 			if v.v.Value == nil {
 				return NoOp, []Value{makeValue(v.idx, v.v)}
 			}
-			switch x := v.v.Value.(type) {
-			case *adt.ListMarker, *adt.StructMarker:
-				expr = v.v
-			default:
-				expr = x
-			}
+			expr = v.v.ActualValue()
 
 		case 1:
 			// the default case, processed below.

internal/core/adt/adt.go

@@ -136,10 +136,16 @@ func Pos(n Node) token.Pos {
 
 func (x *Vertex) Concreteness() Concreteness {
 	// Depends on concreteness of value.
-	if x.Value == nil {
+	switch v := x.Value.(type) {
+	case nil:
 		return Concrete // Should be indetermined.
+
+	case Value:
+		return v.Concreteness()
+
+	default: //  *StructMarker, *ListMarker:
+		return Concrete
 	}
-	return x.Value.Concreteness()
 }
 
 func (x *NodeLink) Concreteness() Concreteness     { return Concrete }

internal/core/adt/composite.go

@@ -255,6 +255,25 @@ func (v *Vertex) UpdateStatus(s VertexStatus) {
 	v.status = s
 }
 
+// ActualValue returns the Value of v without definitions if it is a scalar
+// or itself otherwise.
+func (v *Vertex) ActualValue() Value {
+	// TODO: rename to Value.
+	switch x := v.Value.(type) {
+	// XXX: remove
+	case *StructMarker, *ListMarker:
+		return v
+	case Value:
+		return x
+	default:
+		return v
+	}
+}
+
+func (x *Vertex) IsConcrete() bool {
+	return x.Concreteness() <= Concrete
+}
+
 // IsData reports whether v should be interpreted in data mode. In other words,
 // it tells whether optional field matching and non-regular fields, like
 // definitions and hidden fields, should be ignored.
@@ -385,12 +404,7 @@ func Unwrap(v Value) Value {
 	if !ok {
 		return v
 	}
-	switch x.Value.(type) {
-	case *StructMarker, *ListMarker:
-		return v
-	default:
-		return x.Value
-	}
+	return x.ActualValue()
 }
 
 // Acceptor is a single interface that reports whether feature f is a valid

internal/core/adt/context.go

@@ -449,17 +449,14 @@ func (c *OpContext) getDefault(v Value, scalar bool) (result Value, ok bool) {
 		case *Disjunction:
 			d = t
 
-		case *StructMarker, *ListMarker:
-			return v, true
-
 		case *Vertex:
 			return c.getDefault(t, scalar)
 
 		default:
 			if !scalar {
-				return v, true
+				return x, true
 			}
-			return t, true
+			return x.ActualValue(), true
 		}
 
 	case *Disjunction:
@@ -551,7 +548,7 @@ func (c *OpContext) evalState(v Expr, state VertexStatus) (result Value) {
 		}
 		if isIncomplete(arc) {
 			if arc != nil {
-				return arc.Value
+				return arc.ActualValue() // *Bottom
 			}
 			return nil
 		}