AWS::LanguageExtensions transform breaks with ContainerDependency blocks ECS

[daghaian]

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Tell us about the bug

What goes wrong? Please describe the issue in as much detail as possible.

This issue was encountered when we tried to take advantage of the ForEach intrinsic function provided by LanguageExtensions.

When adding the Transform: AWS::LanguageExtensions block to the top of our previously working stack, any attempts to deploy the stack fail with the error:

Failed to create the changeset: Waiter ChangeSetCreateComplete failed: Waiter encountered a terminal failure state: For expression "Status" we matched expected path: "FAILED" Status: FAILED. Reason: Fragment returned by transform AWS::LanguageExtensions is null

After drilling down into our stack to identify the offending resource, it was found that its specifically the DependsOn container dependency we have defined for our ECS task definition.

To be clear, no additional changes were made to the stack other than the addition of the transform line at the top of the stack.

 -  Name:  test-container
    Image:  nginx
    DependsOn:
      - Condition: COMPLETE
        ContainerName: dependent-container
    MountPoints:
      - ContainerPath: /configs
        SourceVolume: configs
    FirelensConfiguration:
      Type: fluentbit
      Options:
        enable-ecs-log-metadata: "true"
        config-file-type: "file"
        config-file-value: "/configs/parse-json.conf"
    MemoryReservation: 50

Expected behavior

It would be expected that a previously working stack would still be deployable with the inclusion of the LanguageExtensions

Observed behavior

Failure is encountered as mentioned above. Removing only the DependsOn container dependency block resolves the issue but this is not a feasible resolution.

Test cases

Please include a minimal CloudFormation template here that reproduces the issue

Additional context

Anything else we should know?

[daghaian]

Bumping this issue for visibility