pipelines: `fleet` property dropped when merging CodeBuildOptions

[isker]

Describe the bug

Same bug as #35562 but for fleets.

Regression Issue

• Select this option if this issue appears to be a regression.

Last Known Working CDK Library Version

No response

Expected Behavior

fleet is propagated through CodeBuildOptions merging, down to CodeBuild project configuration, such that projects comprising pipeline steps use the configured Fleet.

Current Behavior

That doesn't happen, and the projects stay running on on-demand CodeBuild compute.

Reproduction Steps

const cdkPipeline = new CodePipeline(this, "CodePipeline", {
  synth: new CodeBuildStep("Synth", {
    input: pipelines.CodePipelineSource.connection('my-org/my-app', 'main', {
    connectionArn:
      'arn:aws:codestar-connections:us-east-1:222222222222:connection/7d2469ff-514a-4e4f-9003-5ca4a43cdc41',
    commands: ['npm ci', 'npm run build', 'npx cdk synth'],
  }),
  codeBuildDefaults: {
    buildEnvironment: {
      fleet: new Fleet(this, "Fleet", {
        computeType: FleetComputeType.CUSTOM_INSTANCE_TYPE,
        environmentType: EnvironmentType.LINUX_CONTAINER,
        computeConfiguration: {
          instanceType: new InstanceType("t3.medium"),
        },
      }),
    },
  },
});

Synths things like this:

    "PipelineBuildSynthCdkBuildProjectD03FD7AF": {
      "Properties": {
        // [...]
        "Environment": {
          "ComputeType": "BUILD_GENERAL1_SMALL",
          // Fleet is missing here!
          // "Fleet": {
          //  "FleetArn": {
          //    "Fn::GetAtt": [
          //      "Fleet30813DF3",
          //      "Arn",
          //    ],
          //  },
          // },
          "Image": "aws/codebuild/standard:7.0",
          "ImagePullCredentialsType": "CODEBUILD",
          "PrivilegedMode": false,
          "Type": "LINUX_CONTAINER",
        },
        // [...]
      },
      "Type": "AWS::CodeBuild::Project",
    },

Possible Solution

Repeat https://github.com/aws/aws-cdk/pull/35584/files for fleet.

While you're in there, consider putting both dockerServer and fleet into serializeBuildEnvironment which is right next to mergeBuildEnvironments. These things should be present there.

Additional Information/Context

No response

AWS CDK Library version (aws-cdk-lib)

2.219.0

AWS CDK CLI version

2.1029.4

Node.js Version

N/A

OS

N/A

Language

TypeScript

Language Version

No response

Other information

No response

[isker]

I wonder if you can do some kind of typescript assertion in mergeBuildEnvironments to assert that you are handling all declared properties on BuildEnvironment. This category of bug keeps happening.

[pahud]

Hi @isker,

Thanks for reporting this and for the quick PR #35673! You're absolutely right that this is the same category of bug as #35562 - the fleet property was being dropped during CodeBuildOptions merging.

I really appreciate that you not only fixed fleet and certificate, but also implemented the TypeScript assertion you suggested to prevent this from happening again. The OptionalToUndefined type helper with satisfies is a great solution that
will catch any future properties that get added to BuildEnvironment without being handled in the merge function.

The fix looks solid and the tests confirm everything works as expected. Thanks for the contribution!