internal/core/export: don't wrap embedded scalars in _#def

Issue #977

Change-Id: Ic30a8a86096a0d252ebf0ea12f00f3972dfa63de
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/9842
Reviewed-by: CUE cueckoo <cueckoo@gmail.com>
Reviewed-by: Paul Jolly <paul@myitcv.org.uk>

internal/core/export/export.go

@@ -106,10 +106,10 @@ func (p *Profile) Def(r adt.Runtime, pkgID string, v *adt.Vertex) (*ast.File, er
 
 	if isDef {
 		e.inDefinition--
-		if s, ok := expr.(*ast.StructLit); ok {
+		if v.Kind() == adt.StructKind {
 			expr = ast.NewStruct(
 				ast.Embed(ast.NewIdent("_#def")),
-				ast.NewIdent("_#def"), s,
+				ast.NewIdent("_#def"), expr,
 			)
 		}
 	}

internal/core/export/export_test.go

@@ -189,6 +189,20 @@ func TestGenerated(t *testing.T) {
 		},
 		out: `_#def, _#def: {c: string}`,
 		p:   export.All,
+	}, {
+		// Don't wrap in def if the if the value is an embedded scalar.
+		// Issue #977
+		in: func(r *adt.OpContext) (adt.Expr, error) {
+			v := ctx.CompileString(`
+					#A: { "foo", #enum: 2 }
+				`)
+			v = v.LookupPath(cue.ParsePath("#A"))
+
+			_, n := value.ToInternal(v)
+			return n, nil
+		},
+		out: `"foo", #enum: 2`,
+		p:   export.All,
 	}}
 	for _, tc := range testCases {
 		t.Run("", func(t *testing.T) {