feat(option/internaloption): add WithDefaultEndpointTemplate (#2313)

* Add DefaultEndpointTemplate to internal/settings.go
* Deprecate internaloption.WithDefaultEndpoint

refs: #2264

internal/settings.go

@@ -27,6 +27,7 @@ const (
 type DialSettings struct {
 	Endpoint                      string
 	DefaultEndpoint               string
+	DefaultEndpointTemplate       string
 	DefaultMTLSEndpoint           string
 	Scopes                        []string
 	DefaultScopes                 []string

option/internaloption/internaloption.go

@@ -22,10 +22,29 @@ func (o defaultEndpointOption) Apply(settings *internal.DialSettings) {
 // It should only be used internally by generated clients.
 //
 // This is similar to WithEndpoint, but allows us to determine whether the user has overridden the default endpoint.
+//
+// Deprecated: WithDefaultEndpoint does not support setting the universe domain.
+// Use WithDefaultEndpointTemplate and WithDefaultUniverseDomain to compose the
+// default endpoint instead.
 func WithDefaultEndpoint(url string) option.ClientOption {
 	return defaultEndpointOption(url)
 }
 
+type defaultEndpointTemplateOption string
+
+func (o defaultEndpointTemplateOption) Apply(settings *internal.DialSettings) {
+	settings.DefaultEndpointTemplate = string(o)
+}
+
+// WithDefaultEndpointTemplate provides a template for creating the endpoint
+// using a universe domain. See also WithDefaultUniverseDomain and
+// option.WithUniverseDomain.
+//
+// It should only be used internally by generated clients.
+func WithDefaultEndpointTemplate(url string) option.ClientOption {
+	return defaultEndpointTemplateOption(url)
+}
+
 type defaultMTLSEndpointOption string
 
 func (o defaultMTLSEndpointOption) Apply(settings *internal.DialSettings) {

option/internaloption/internaloption_test.go

@@ -35,6 +35,7 @@ func TestWithCredentials(t *testing.T) {
 func TestDefaultApply(t *testing.T) {
 	opts := []option.ClientOption{
 		WithDefaultEndpoint("https://example.com:443"),
+		WithDefaultEndpointTemplate("https://foo.%s/"),
 		WithDefaultMTLSEndpoint("http://mtls.example.com:445"),
 		WithDefaultScopes("a"),
 		WithDefaultUniverseDomain("foo.com"),
@@ -45,11 +46,12 @@ func TestDefaultApply(t *testing.T) {
 		opt.Apply(&got)
 	}
 	want := internal.DialSettings{
-		DefaultScopes:         []string{"a"},
-		DefaultEndpoint:       "https://example.com:443",
-		DefaultUniverseDomain: "foo.com",
-		DefaultAudience:       "audience",
-		DefaultMTLSEndpoint:   "http://mtls.example.com:445",
+		DefaultScopes:           []string{"a"},
+		DefaultEndpoint:         "https://example.com:443",
+		DefaultEndpointTemplate: "https://foo.%s/",
+		DefaultUniverseDomain:   "foo.com",
+		DefaultAudience:         "audience",
+		DefaultMTLSEndpoint:     "http://mtls.example.com:445",
 	}
 	if !cmp.Equal(got, want, cmpopts.IgnoreUnexported(grpc.ClientConn{}), cmpopts.IgnoreFields(google.Credentials{}, "universeDomain")) {
 		t.Errorf(cmp.Diff(got, want, cmpopts.IgnoreUnexported(grpc.ClientConn{}), cmpopts.IgnoreFields(google.Credentials{}, "universeDomain")))