[aws-apigateway] BasePathMapping does not configure stage for SpecRestApi with domainName

[marcogrcr]

When I create a RestApi specifying a value for domainName the underlying CfnBasePathMapping gets configured correctly:

{
  "DomainName": { "Ref": "..." },
  "RestApiId": { "Ref": "..." },
  "Stage": { "Ref": "..." }
}

However, when I use SpecRestApi with domainName, the underlying CfnBasePathMapping omits the stage field:

{
  "DomainName": { "Ref": "..." },
  "RestApiId": { "Ref": "..." }
}

Reproduction Steps

import { RestApi, SpecRestApi } from "@aws-cdk/aws-apigateway";
import { Stack } from "@aws-cdk/core";

const stack = new Stack();

new RestApi(stack, "MyRestApi", {
  // (...)
  domainName: { /* (...) */ }
}).api.root.addMethod("GET");;

new SpecRestApi(stack, "MySpecRestApi", {
  // (...)
  domainName: { /* (...) */ }
});

What did you expect to happen?

The AWS::ApiGateway::BasePathMapping resource generated by SpecRestApi is equivalent to the one generated by RestApi.

What actually happened?

The AWS::ApiGateway::BasePathMapping resource generated by SpecRestApi omits the Stage field.

Environment

• CLI Version: v1.62.0
• Framework Version: v1.62.0
• Node.js Version: v12.13.0
• OS: Mac OS v10.14.6
• Language (Version): TypeScript v3.9.6

Other

I believe the root cause of this bug is here:

aws-cdk/packages/@aws-cdk/aws-apigateway/lib/base-path-mapping.ts

Lines 57 to 66 in 8c2d7fc

	const stage = props.stage ?? (props.restApi instanceof RestApi
	? props.restApi.deploymentStage
	: undefined);
	new CfnBasePathMapping(this, 'Resource', {
	basePath: props.basePath,
	domainName: props.domainName.domainName,
	restApiId: props.restApi.restApiId,
	stage: stage && stage.stageName,
	});

I believe props.restApi instanceof RestApi should be replaced with props.restApi instanceof RestApiBase.

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This is 🐛 Bug Report

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