cue/ast: add NewBool helper

Change-Id: Iccd88259a08d00e5da589b962a69e675e39a6234
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/4460
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>

cue/ast/ast.go

@@ -423,6 +423,20 @@ func NewString(str string) *BasicLit {
 	return &BasicLit{Kind: token.STRING, ValuePos: token.NoPos, Value: str}
 }
 
+// NewBool creates a new BasicLit with a bool value without position.
+// Useful for ASTs generated by code other than the CUE parser.
+func NewBool(b bool) *BasicLit {
+	x := &BasicLit{}
+	if b {
+		x.Kind = token.TRUE
+		x.Value = "true"
+	} else {
+		x.Kind = token.FALSE
+		x.Value = "false"
+	}
+	return x
+}
+
 // TODO:
 // - use CUE-specific quoting (hoist functionality in export)
 // - NewBytes

cue/ast/ident_test.go

@@ -58,7 +58,7 @@ func TestLabelName(t *testing.T) {
 		isIdent: false,
 		err:     true,
 	}, {
-		in:      &ast.BasicLit{Kind: token.TRUE, Value: "true"},
+		in:      ast.NewBool(true),
 		out:     "true",
 		isIdent: true,
 	}, {