bugfix/integrate_intrinsics

[viksrivat]

Issue #, if available:
There was a bug when dealing with layers and intrinsics. This is an update to add tests and to address it.
Description of changes:

Checklist:

• Write Design Document (Do I need to write a design document?)
• Write unit tests
• Write/update functional tests
• Write/update integration tests
• make pr passes
• Write documentation

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[viksrivat]

The integrate_intrinsics pr failed because LambdaLayers were handling Refs in a different way than the default resolver. I now handle LambdaLayers as a special case since unresolved Refs become {"Ref": "logical_id"}.

Before: SamTranslator was run and left attributes such as {"Ref": "value"} -> {"Ref": "value"}. The translator would leave the following resource as is.

StageTest:
     Properties:
          RestApiId: !Ref Value

However, we need to resolve these attributes in order to fully resolve intrinsics. After running a pass through the SamTranslator then IntrinsicResolver. Now, what we do is convert it to

StageTest:
     Properties:
          RestApiId: Value

This is because SamTranslator resolves a ref such as {"Ref": "AWS::Region"} to {"Ref": "us-east-1"}. It also replaces Global Attributes directly into the relevant resources. However, we want {"Ref": "AWS::Region"} to become "us-east-1". Thus, by default we take {"Ref": "value"} -> "value".

To provide support for the special LambdaLayer case, I extended the IntrinsicSymbolTable to use

        {
            "AWS::ApiGateway::RestApi": {
                "RootResourceId": "/"  # It usually used as a reference to the parent id of the RestApi,
            },
            "AWS::Lambda::LayerVersion": {
                IntrinsicResolver.REF: lambda logical_id: {IntrinsicResolver.REF: logical_id}
            },
            "AWS::Serverless::LayerVersion": {
                IntrinsicResolver.REF: lambda logical_id: {IntrinsicResolver.REF: logical_id}
            }
        }

In terms of dealing and managing intrinsics cases such as this, this implementation is not inclusive of all ways to process Refs and Fn::GetAtt. There doesn't seem to be a good standard that CloudFormation has set for all Refs and Fn::GetAtts. We need to either add special support for more types as time goes on or find another way to deal with maintaining intrinsics in the longer term.

[sriram-mv]

Thanks for the fix @viksrivat!