fix: Allow Pub/Sub Topic update to remove schema settings

.changelog/11038.txt

@@ -0,0 +1,3 @@
+```release-note:breaking-change
+pubsub: Allow `schema_settings` of `google_pubsub_topic` to be removed
+```

google-beta/services/pubsub/resource_pubsub_topic.go

@@ -169,7 +169,6 @@ and is not a valid configuration.`,
 			},
 			"schema_settings": {
 				Type:        schema.TypeList,
-				Computed:    true,
 				Optional:    true,
 				Description: `Settings for validating messages published against a schema.`,
 				MaxItems:    1,

google-beta/services/pubsub/resource_pubsub_topic_test.go

@@ -95,6 +95,9 @@ func TestAccPubsubTopic_schema(t *testing.T) {
 			{
 				Config: testAccPubsubTopic_updateWithNewSchema(topic, schema2),
 			},
+			{
+				Config: testAccPubsubTopic_updateWithNewSchema(topic, ""),
+			},
 			{
 				ResourceName:      "google_pubsub_topic.bar",
 				ImportStateId:     topic,
@@ -230,7 +233,8 @@ resource "google_pubsub_topic" "bar" {
 }
 
 func testAccPubsubTopic_updateWithNewSchema(topic, schema string) string {
-	return fmt.Sprintf(`
+	if schema != "" {
+		return fmt.Sprintf(`
 resource "google_pubsub_schema" "foo" {
 	name = "%s"
 	type = "PROTOCOL_BUFFER"
@@ -245,6 +249,13 @@ resource "google_pubsub_topic" "bar" {
   }
 }
 `, schema, topic)
+	} else {
+		return fmt.Sprintf(`
+		resource "google_pubsub_topic" "bar" {
+			name = "%s"
+		}
+		`, topic)
+	}
 }
 
 func testAccPubsubTopic_updateWithKinesisIngestionSettings(topic string) string {

website/docs/guides/version_6_upgrade.html.markdown

@@ -113,3 +113,9 @@ Description of the change and how users should adjust their configuration (if ne
 ### `settings.ip_configuration.require_ssl` is now removed
 
 Removed in favor of field `settings.ip_configuration.ssl_mode`.
+
+## Resource: `google_pubsub_topic`
+
+### `schema_settings` no longer has a default value
+
+An empty value means the setting should be cleared.