fix(internal/librarian/golang): do not add transport in gapic options (#4155)

Do not add transport in gapic options for Go clients. Some libraries,
e.g., `apigeeconnect`, `apigeeregistry` and `beyondcorp` do not have
transport in gapic options.

For #3617

Author: JoeWang1127

internal/librarian/golang/generate.go

@@ -203,7 +203,9 @@ func buildGAPICOpts(apiPath string, library *config.Library, goAPI *config.GoAPI
 	// TODO(https://github.com/googleapis/librarian/issues/3775): assuming
 	// transport is library-wide for now, until we have figured out the config
 	// for transports.
-	opts = append(opts, "transport="+transport(sc))
+	if trans := transport(sc); trans != "" {
+		opts = append(opts, "transport="+trans)
+	}
 	level, err := releaseLevel(apiPath, library.Version)
 	if err != nil {
 		return nil, err

internal/librarian/golang/generate_test.go

@@ -838,6 +838,23 @@ func TestBuildGAPICOpts_Success(t *testing.T) {
 				"release-level=ga",
 			},
 		},
+		{
+			name:    "no transport",
+			apiPath: "google/cloud/apigeeconnect/v1",
+			library: &config.Library{
+				Name:    "apigeeconnect",
+				Version: "1.2.3",
+				APIs:    []*config.API{{Path: "google/cloud/apigeeconnect/v1"}},
+			},
+			googleapisDir: googleapisDir,
+			want: []string{
+				"go-gapic-package=cloud.google.com/go/apigeeconnect/apiv1;apigeeconnect",
+				"metadata",
+				"rest-numeric-enums",
+				"api-service-config=" + filepath.Join(googleapisDir, "google/cloud/apigeeconnect/v1/apigeeconnect_1.yaml"),
+				"release-level=ga",
+			},
+		},
 	} {
 		t.Run(test.name, func(t *testing.T) {
 			t.Parallel()

internal/serviceconfig/sdk.yaml

@@ -212,6 +212,7 @@
 - path: google/cloud/apigeeconnect/v1
   transports:
     csharp: grpc+rest
+    go: ""
     java: grpc+rest
     nodejs: grpc+rest
     php: grpc+rest
@@ -223,6 +224,7 @@
   path: google/cloud/apigeeregistry/v1
   transports:
     csharp: grpc+rest
+    go: ""
     java: grpc+rest
     nodejs: grpc+rest
     php: grpc+rest
@@ -290,6 +292,7 @@
 - path: google/cloud/beyondcorp/appconnections/v1
   transports:
     csharp: grpc
+    go: ""
     java: grpc
     nodejs: grpc+rest
     php: grpc+rest
@@ -298,6 +301,7 @@
 - path: google/cloud/beyondcorp/appconnectors/v1
   transports:
     csharp: grpc
+    go: ""
     java: grpc
     nodejs: grpc+rest
     php: grpc+rest
@@ -306,6 +310,7 @@
 - path: google/cloud/beyondcorp/appgateways/v1
   transports:
     csharp: grpc
+    go: ""
     java: grpc
     nodejs: grpc+rest
     php: grpc+rest
@@ -314,6 +319,7 @@
 - path: google/cloud/beyondcorp/clientconnectorservices/v1
   transports:
     csharp: grpc
+    go: ""
     java: grpc
     nodejs: grpc+rest
     php: grpc+rest
@@ -322,6 +328,7 @@
 - path: google/cloud/beyondcorp/clientgateways/v1
   transports:
     csharp: grpc
+    go: ""
     java: grpc
     nodejs: grpc+rest
     php: grpc+rest

internal/testdata/googleapis/google/cloud/apigeeconnect/v1/apigeeconnect_1.yaml

@@ -0,0 +1,2 @@
+type: google.api.Service
+name: apigeeconnect.googleapis.com