feat: expose experimental universe-related options (#2264)

This PR adds the first step in plumbing a universe option into clients
by first exposing it as part of the option package.

It exposes a `WithUniverse(string)` as a public option, and `WithDefaultUniverse(string)`
as an internal option that can be used by generated clients.  It also augments existing
tests.

It does not yet include any behavioral changes.

internal/settings.go

@@ -55,6 +55,8 @@ type DialSettings struct {
 	EnableDirectPathXds           bool
 	EnableNewAuthLibrary          bool
 	AllowNonDefaultServiceAccount bool
+	UniverseDomain                string
+	DefaultUniverseDomain         string
 
 	// Google API system parameters. For more information please read:
 	// https://cloud.google.com/apis/docs/system-parameters

option/internaloption/internaloption.go

@@ -126,6 +126,22 @@ func (w withDefaultScopes) Apply(o *internal.DialSettings) {
 	copy(o.DefaultScopes, w)
 }
 
+// WithDefaultUniverseDomain returns a ClientOption that sets the default universe domain.
+//
+// It should only be used internally by generated clients.
+//
+// This is similar to the public WithUniverse, but allows us to determine whether the user has
+// overridden the default universe.
+func WithDefaultUniverseDomain(ud string) option.ClientOption {
+	return withDefaultUniverseDomain(ud)
+}
+
+type withDefaultUniverseDomain string
+
+func (w withDefaultUniverseDomain) Apply(o *internal.DialSettings) {
+	o.DefaultUniverseDomain = string(w)
+}
+
 // EnableJwtWithScope returns a ClientOption that specifies if scope can be used
 // with self-signed JWT.
 func EnableJwtWithScope() option.ClientOption {

option/internaloption/internaloption_test.go

@@ -7,9 +7,13 @@ package internaloption
 import (
 	"testing"
 
+	"github.com/google/go-cmp/cmp"
+	"github.com/google/go-cmp/cmp/cmpopts"
 	"golang.org/x/oauth2"
 	"golang.org/x/oauth2/google"
 	"google.golang.org/api/internal"
+	"google.golang.org/api/option"
+	"google.golang.org/grpc"
 )
 
 func TestWithCredentials(t *testing.T) {
@@ -27,3 +31,27 @@ func TestWithCredentials(t *testing.T) {
 		t.Errorf("ts.Token() = %q, want %q", tok.AccessToken, "")
 	}
 }
+
+func TestDefaultApply(t *testing.T) {
+	opts := []option.ClientOption{
+		WithDefaultEndpoint("https://example.com:443"),
+		WithDefaultMTLSEndpoint("http://mtls.example.com:445"),
+		WithDefaultScopes("a"),
+		WithDefaultUniverseDomain("foo.com"),
+		WithDefaultAudience("audience"),
+	}
+	var got internal.DialSettings
+	for _, opt := range opts {
+		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",
+	}
+	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")))
+	}
+}

option/option.go

@@ -343,3 +343,16 @@ func (w *withCreds) Apply(o *internal.DialSettings) {
 func WithCredentials(creds *google.Credentials) ClientOption {
 	return (*withCreds)(creds)
 }
+
+// WithUniverseDomain returns a ClientOption that sets the universe domain.
+//
+// This is an EXPERIMENTAL API and may be changed or removed in the future.
+func WithUniverseDomain(ud string) ClientOption {
+	return withUniverseDomain(ud)
+}
+
+type withUniverseDomain string
+
+func (w withUniverseDomain) Apply(o *internal.DialSettings) {
+	o.UniverseDomain = string(w)
+}

option/option_test.go

@@ -73,6 +73,7 @@ func TestApply(t *testing.T) {
 		WithQuotaProject("user-project"),
 		WithRequestReason("Request Reason"),
 		WithTelemetryDisabled(),
+		WithUniverseDomain("universe.com"),
 	}
 	var got internal.DialSettings
 	for _, opt := range opts {
@@ -91,6 +92,7 @@ func TestApply(t *testing.T) {
 		QuotaProject:      "user-project",
 		RequestReason:     "Request Reason",
 		TelemetryDisabled: true,
+		UniverseDomain:    "universe.com",
 	}
 	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")))