SAM Local Layers not included when intrinsic functions are used

[martysweet]

Description:
A list of layers are not used if !Sub is used (or possibly any other intrinsic function) when using the local invoke or start-api functionality. No error is thrown to alert the user than intrinsic functions may not be supported.

Steps to reproduce the issue:

1. Create template, an example from https://github.com/stackery/php-lambda-layer

AWSTemplateFormatVersion: 2010-09-09
Description: My PHP Application
Transform: AWS::Serverless-2016-10-31
Resources:
  phpserver:
    Type: AWS::Serverless::Function
    Properties:
      FunctionName: !Sub ${AWS::StackName}-phpserver
      Description: PHP Webserver
      CodeUri: src/php
      Runtime: provided
      Handler: index.php
      MemorySize: 3008
      Timeout: 30
      Tracing: Active
      Layers:
        - !Sub arn:aws:lambda:${AWS::Region}:887080169480:layer:php71:5
      Events:
        api:
          Type: Api
          Properties:
            Path: /{proxy+}
            Method: ANY

2. Invoke the function with sam local invoke phpserver --no-event
3. Get error message

Observed result:
As the layer was not included, the bootstrap file is not present.

{
  "errorType": "Runtime.ExitError",
  "errorMessage": "RequestId: 52fdfc07-2182-154f-163f-5f0f9a621d72 Error: Couldn't find valid bootstrap(s): [/var/task/bootstrap /opt/bootstrap]"
}

Expected result:
The layer is included and the function invokes as expected.

Workaround:
Define a string for each element of the Layers array, for example:

  Layers:
        - arn:aws:lambda:eu-west-1:887080169480:layer:php71:5

This then works as expected.

Output of sam --version:
0.8.1 and tested on develop branch

Optional Debug logs:

Add --debug flag to command you are running

Broken example (using !Sub)

2018-12-05 19:56:28 Max number of attempts exceeded (1) when attempting to retrieve data from metadata service.
2018-12-05 19:56:28 Resolving code path. Cwd=/srv/development/abcd, CodeUri=src/php
2018-12-05 19:56:28 Resolved absolute path to code is /srv/development/abcd/src/php
2018-12-05 19:56:28 Code /srv/development/abcd/src/php is not a zip/jar file
2018-12-05 19:56:28 Skipping building an image since no layers were defined

Working example (using a strict String)

2018-12-05 19:57:50 Resolving code path. Cwd=/srv/development/abcd, CodeUri=src/php
2018-12-05 19:57:50 Resolved absolute path to code is /srv/development/abcd/src/php
2018-12-05 19:57:50 Code /srv/development/abcd/src/php is not a zip/jar file
2018-12-05 19:57:50 Event before-parameter-build.lambda.GetLayerVersion: calling handler <function generate_idempotent_uuid at 0x7f2a7a4856e0>
2018-12-05 19:57:50 Making request for OperationModel(name=GetLayerVersion) with params: {'body': '', 'url': u'https://lambda.eu-west-1.amazonaws.com/2018-10-31/layers/arn%3Aaws%3Alambda%3Aeu-west-1%3A887080169480%3Alayer%3Aphp71/versions/4', 'headers': {'User-Agent': 'Boto3/1.9.57 Python/2.7.12 Linux/4.4.0-122-generic Botocore/1.12.59'}, 'context': {'auth_type': None, 'client_region': 'eu-west-1', 'has_streaming_input': False, 'client_config': <botocore.config.Config object at 0x7f2a75ea05d0>}, 'query_string': {}, 'url_path': u'/2018-10-31/layers/arn%3Aaws%3Alambda%3Aeu-west-1%3A887080169480%3Alayer%3Aphp71/versions/4', 'method': u'GET'}

I've seen #573, I assume this is related. Hopefully this issue will help someone from wasting a few hours on the same thing 👍

[jfuss]

Duplicate of #813 and #528

Closing.