(cli): cdk migrate fails to process Fn::Sub within Fn::ImportValue

[danielfen]

Describe the bug

It is common to use the intrinsic function Fn::Sub within Fn::ImportValue, to import cross-stack values in an environment-specific way (e.g. selecting on a dev, test or production environment stack export). An example of this syntax is given on the Fn::ImportValue dcumentation: https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-importvalue.html#w9aac34c28c46c15

The CDK Migrate CLI command fails currently when processing templates containing this syntax with the error

Migrate failed for `<stack name>`: stack generation failed due to error '<Resource Path>.Fn::ImportValue: invalid type: map, expected a string at ...'

stack generation failed due to error '<Resource Path>.Fn::ImportValue: invalid type: map, expected a string at ...'

Expected Behavior

cdk migrate to be able to generate CDK code for templates containing

"Fn::ImportValue": {
  "Fn::Sub": [
    "${Value}...",
    {
      "Value": {
        "Ref": "ParameterName"
      }
    }
  ]
}

Current Behavior

An error raised due to the Fn::Sub within Fn::ImportValue not being a string value

Reproduction Steps

Run cdk migrate --stack-name my-stack --language typescript --from-path <template> --output-path <path for output> using the following template:

{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Parameters": {
    "EnvironmentName": {
      "Description": "Environment used for this deployment.",
      "Type": "String",
      "AllowedValues": [
        "dev",
        "stage",
        "prod"
      ]
    }
  },
  "Resources": {
    "MyApi5xxErrorsAlarm": {
      "Type": "AWS::CloudWatch::Alarm",
      "Properties": {
        "AlarmDescription": "Example alarm",
        "Namespace": "AWS/ApiGateway",
        "Dimensions": [
          {
            "Name": "ApiName",
            "Value": "MyApi"
          }
        ],
        "MetricName": "5XXError",
        "ComparisonOperator": "GreaterThanThreshold",
        "Statistic": "Average",
        "Threshold": 0,
        "Period": 900,
        "EvaluationPeriods": 1,
        "TreatMissingData": "notBreaching",
        "AlarmActions": [
          {
            "Fn::ImportValue": {
              "Fn::Sub": [
                "${Environment}AlarmsTopicArn",
                {
                  "Environment": {
                    "Ref": "EnvironmentName"
                  }
                }
              ]
            }
          }
        ]
      }
    }
  }
}

The error will be raised

Run the same command with the following template and the template is processed successfully:

{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Parameters": {
    "EnvironmentName": {
      "Description": "Environment used for this deployment.",
      "Type": "String",
      "AllowedValues": [
        "dev",
        "stage",
        "prod"
      ]
    }
  },
  "Resources": {
    "MyApi5xxErrorsAlarm": {
      "Type": "AWS::CloudWatch::Alarm",
      "Properties": {
        "AlarmDescription": "Example alarm",
        "Namespace": "AWS/ApiGateway",
        "Dimensions": [
          {
            "Name": "ApiName",
            "Value": "MyApi"
          }
        ],
        "MetricName": "5XXError",
        "ComparisonOperator": "GreaterThanThreshold",
        "Statistic": "Average",
        "Threshold": 0,
        "Period": 900,
        "EvaluationPeriods": 1,
        "TreatMissingData": "notBreaching",
        "AlarmActions": [
          {
            "Fn::ImportValue": "devAlarmsTopicArn"
          }
        ]
      }
    }
  }
}

Possible Solution

No response

Additional Information/Context

No response

CDK CLI Version

2.126.0 (build fb74c41)

Framework Version

No response

Node.js Version

v18.17.1

OS

20.04.6 LTS (Focal Fossa)

Language

TypeScript

Language Version

No response

Other information

No response

[tim-finnigan]

Thanks for reporting this issue, I could reproduce the error.

[TheRealAmazonKendra]

Looks like the recursion doing the translating is not going deep enough. Adding this task to cdk-from-cfn for fixing.

[TheRealAmazonKendra]

The fix for this was released in v2.132.

[github-actions]

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