tiltfile: make a link object a struct (#3843)

internal/tiltfile/links/links.go

@@ -6,6 +6,7 @@ import (
 
 	"github.com/pkg/errors"
 	"go.starlark.net/starlark"
+	"go.starlark.net/starlarkstruct"
 
 	"github.com/tilt-dev/tilt/pkg/model"
 
@@ -14,29 +15,12 @@ import (
 )
 
 type Link struct {
+	*starlarkstruct.Struct
 	model.Link
 }
 
 var _ starlark.Value = Link{}
 
-func (l Link) String() string {
-	return fmt.Sprintf("Link(url=%q, name=%q)", l.URL, l.Name)
-}
-
-func (l Link) Type() string {
-	return "Link"
-}
-
-func (l Link) Freeze() {}
-
-func (l Link) Truth() starlark.Bool {
-	return l.Link != model.Link{}
-}
-
-func (l Link) Hash() (uint32, error) {
-	return 0, fmt.Errorf("unhashable type: port_forward")
-}
-
 // Parse resource links (string or `link`) into model.Link
 // Not to be confused with a LinkED List :P
 type LinkList struct {
@@ -117,6 +101,10 @@ func (e Extension) link(thread *starlark.Thread, fn *starlark.Builtin, args star
 	}
 
 	return Link{
+		Struct: starlarkstruct.FromStringDict(starlark.String("link"), starlark.StringDict{
+			"url":  starlark.String(withScheme),
+			"name": starlark.String(name),
+		}),
 		Link: model.Link{
 			URL:  withScheme,
 			Name: name,

internal/tiltfile/links/links_test.go

@@ -3,7 +3,10 @@ package links
 import (
 	"testing"
 
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+
+	"github.com/tilt-dev/tilt/internal/tiltfile/starkit"
 )
 
 func TestMaybeAddScheme(t *testing.T) {
@@ -42,3 +45,31 @@ func TestMaybeAddScheme(t *testing.T) {
 		})
 	}
 }
+
+func TestLinkProps(t *testing.T) {
+	f := starkit.NewFixture(t, NewExtension())
+	defer f.TearDown()
+
+	f.File("Tiltfile", `
+l = link("localhost:4000", "web")
+print(l.url)
+print(l.name)
+`)
+
+	_, err := f.ExecFile("Tiltfile")
+	require.NoError(t, err)
+	assert.Equal(t, "localhost:4000\nweb\n", f.PrintOutput())
+}
+func TestLinkPropsImmutable(t *testing.T) {
+	f := starkit.NewFixture(t, NewExtension())
+	defer f.TearDown()
+
+	f.File("Tiltfile", `
+l = link("localhost:4000", "web")
+l.url = "XXX"
+`)
+
+	_, err := f.ExecFile("Tiltfile")
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "can't assign to .url field of struct")
+}