ChangeSet creation failure with {{IntrinsicFunction:(stack_name)//Fn::ImportValue}} is not allowed.

[mrlikl]

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Tell us about the bug

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

When a nested stack is referencing a parameter that is passed from the root/parent stack as intrinsic functions, a similar error Usage of {{IntrinsicFunction:stack_name//Fn::ImportValue}} is not allowed. Usage of {{IntrinsicFunction:stack_name/logical_idFn::GetAtt}} is not allowed. is occurring

Expected behavior

Change set to be successfully create

Observed behavior

Change set failure with the error

Test cases

Please include a minimal CloudFormation template here that reproduces the issue

Create a stack with simple S3 bucket

root.yml

AWSTemplateFormatVersion: "2010-09-09"
Resources:
  RootS3Bucket:
    Type: AWS::S3::Bucket

Create change set with a nested stack like below -

root.yml

AWSTemplateFormatVersion: "2010-09-09"
Resources:
  TestRule:
    Type: AWS::CloudFormation::Stack
    Properties:
      TemplateURL: nested.yml
      Parameters:
        TagValue: !GetAtt RootS3Bucket.Arn
  RootS3Bucket:
    Type: AWS::S3::Bucket

nested.yml

AWSTemplateFormatVersion: 2010-09-09
Transform: 'AWS::LanguageExtensions'

Parameters:
  TagValue:
    Type: String

Resources:
  'Fn::ForEach::Buckets':
    - Names
    - - Store1
      - Store2
    - '${Names}Bucket':
        Type: 'AWS::S3::Bucket'
        Properties:
          Tags:
            - Key: parameters
              Value: !Ref TagValue

Additional context

Anything else we should know?

[nsmedira]

I am also seeing this behavior. I believe that the use of Transform: 'AWS::LanguageExtensions' is correlated with the error.

Like you, I have a nested stack whose input parameters are the result of intrinsic functions in the parent stack. I am also using Transform: 'AWS::LanguageExtensions' in order to add Fn::ForEach to a previously-working nested template. Merely adding Transform: 'AWS::LanguageExtensions' to this previously-working nested template causes the illegal usage error described above.