Motivation

We have had many requests for the Language Extensions Transform. These provide additional useful functionality to CloudFormation.

In particular, the Fn::ForEach function is useful for generating many templated resources.

Changes

Unfortunately the implementation is quite dense, relying on recurse_object which creates some complex situations. Though I found it quite straightforward to write the implementation, I feel it might be confusing to read.

• (minor) refactor resolve_refs_recursively to use a ResolveRefsRecursivelyContext dataclass with resolve(thing) method
  • only use it partially since we don't plan on keeping this implementation
• Add fixture for deploying a template with transform, then calling get_template and get_template_resources
• Implement Fn::Length
• Implement Fn::ForEach for a simple case (taken from AWS docs)
• Implement Fn::ForEach for a specific customer use case
• Implement Fn::ForEach for a nested use case (taken from AWS docs)
• Implement Fn::ToJsonString for use case from AWS docs
• Add unit test for expand_fn_foreach so we can quicker iterate cases that don't require deployment of CFn templates