New Fn::ForEach function breaks cloudformation package CLI

[JeremieRodon]

Describe the bug

When using aws cloudformation package on a template file that uses Transform: AWS::LanguageExtensions with Fn::ForEach, the command fails with the message:
'list' object has no attribute 'get'

Expected Behavior

aws cloudformation package should accept any syntax accepted by the CloudFormation service engine.

Current Behavior

aws cloudformation package fails with 'list' object has no attribute 'get' when using a template with the Fn::ForEach language extension.

Reproduction Steps

This is a valid CloudFormation template that will create two InternetGateways:

AWSTemplateFormatVersion: 2010-09-09
Transform: AWS::LanguageExtensions
Resources:
  Fn::ForEach::IGW:
  - index
  - ['A', 'B']
  - IGW${index}:
      Type: AWS::EC2::InternetGateway
      Properties:
        Tags:
        - Key: Name
          Value: !Sub igw-${index}

If you save that in a file named igws.yml and try this:
aws cloudformation package --template-file igws.yml --s3-bucket some-bucket --output-template-file igws-new.yml
It will throw the exception

Possible Solution

It fails because the Resource bloc usually only contains sub-objects like:

Resources:
  VPC:
    Type: AWS::EC2::VPC
    Properties:
      [clip...]

With the Fn::ForEach, we must define a list, like:

Resources:
  Fn::ForEach::Subnets:
  - index
  - ['A', 'B']
  - [clip...]

I guess the CLI parser is expecting anything under Resources to be a Python dictionary with a Type key so it tries to get that.
When it tries to do so on the Fn::ForEach list, that throws 'list' object has no attribute 'get'

Additional Information/Context

No response

CLI version used

aws-cli/2.13.5

Environment details (OS name and version, etc.)

Windows 10

[JeremieRodon]

Update: It also fails when packaging a template with nested templates when one of the nested templates uses the Fn::ForEach

[aBurmeseDev]

Hi @JeremieRodon - thanks for reporting this behavior. I was able to reproduce it on my end and we will need to further investigate with the team. I'll post here once we have an update.

[aBurmeseDev]

From further discussion with the team, we have been advised to refer users of CloudFormation package to the AWS SAM CLI and sam-package command. Any changes related to the CloudFormation customization are currently not prioritized but you're welcome to submit contribution PR on this and the team will be able to take a look.
As an alternative, are you able to use the AWS SAM CLI or do you know if this issue present there as well?

[dansepp-gale]

As best I can tell, this is an issue with the AWS SAM CLI as well.

[richard-grainger-veeva]

I am also seeing this issue.

[tim-finnigan]

Just wanted to follow up and let everyone know that we are aware of the issue, and the team owning the CloudFormation customization is planning to work on it. Also found a related issue in the SAM CLI repository: aws/aws-sam-cli#5647

[hssyoo]

The Fn::ForEach intrinsic function is available in v1 and v2: #8096

[github-actions]

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