using clean produces invalid template

[rickalm]

we are using new_template = to_yaml( to_json( orig_template ) ) to cleanup the yaml we are producing with jinja2

clean_up=False we see

  PublicSubnetIds:
    Description: The public subnetids
    Condition: HasPublicSubnet1AZ1
    Value:
      Fn::Join:
        - ','
        -
          - Fn::If:
            - HasPublicSubnet1AZ1
            - !Ref PublicSubnet1AZ1
            - !Ref AWS::NoValue
          - Fn::If:
            - HasPublicSubnet1AZ2
            - !Ref PublicSubnet1AZ2
            - !Ref AWS::NoValue
          - Fn::If:
            - HasPublicSubnet1AZ3
            - !Ref PublicSubnet1AZ3
            - !Ref AWS::NoValue
    Export:
      Name: !Sub vpc-${Environment}-PublicSubnetIds

but with clean_up=True we get

  PublicSubnetIds:
    Description: The public subnetids
    Condition: HasPublicSubnet1AZ1
    Value: !Sub
      - ${Param1},${Param2},${Param3}
      - Param1: !If
          - HasPublicSubnet1AZ1
          - !Ref 'PublicSubnet1AZ1'
          - !Ref 'AWS::NoValue'
        Param2: !If
          - HasPublicSubnet1AZ2
          - !Ref 'PublicSubnet1AZ2'
          - !Ref 'AWS::NoValue'
        Param3: !If
          - HasPublicSubnet1AZ3
          - !Ref 'PublicSubnet1AZ3'
          - !Ref 'AWS::NoValue'
    Export:
      Name: !Sub 'vpc-${Environment}-PublicSubnetIds'

Which CloudFormation complains about .. suggestions ??

[stilvoid]

Well, you've found one of the rare cases where a Join is the correct choice over a Sub. Unfortunately, cfn-flip doesn't (yet) have a way to detect this and so will make the opinionated decision that a Sub is always preferable to a Join.

It might be valid to fix this by checking if AWS::NoValue is used anywhere in a Join and then leave is as a Join. I'll try this out later today.