Add Support for Shorthand CloudFormation Syntax

[laardee]

What did you implement:

This PR adds support for shorthand CloudFormation syntax, e.g. !Ref, !GetAtt and !Join.

This should not be a breaking change, least I don't know any cases where !Something syntax is used in serverless.yml.

How did you implement it:

This feature leverages js-yaml module's custom schema.

How can we verify it:

service: shorthand-cf

provider:
  name: aws
  runtime: nodejs6.10
  iamRoleStatements:
    - Effect: "Allow"
      Action:
        - "kms:Decrypt"
      Resource: !Join
        - ":"
        - - "arn:aws:kms"
          - !Ref AWS::Region
          - !Ref AWS::AccountId
          - ":key/CMK_key_ID"
    - Effect: "Allow"
      Action:
        - "s3:*"
      Resource:
        - !Join
          - ":"
          - - "arn:aws:s3::"
            - !Ref "MyBucket"
        - !Join
          - ":"
          - - "arn:aws:s3::"
            - !Ref "MyBucket"
            - "/*"

functions:
  hello:
    handler: handler.hello

resources:
  Conditions:
    AndCondition: !And 
      - !Not [!Equals ["prod", "${opt:stage, self:provider.stage}"]]
      - !Not [!Equals ["staging", "${opt:stage, self:provider.stage}"]]

  Resources:
    MyBucket:
      Type: AWS::S3::Bucket
      Properties:
        Tags:
          - Key: FruitTag # fruit tag is the most obvious use case
            Value: !Select [ !If [AndCondition, "0", "1"], [ "apples", "grapes" ] ]

  Outputs:
    BucketName:
      Description: "My bucket name"
      Value: !Ref MyBucket
    BucketArn:
      Description: "My Bucket arn"
      Value: !GetAtt MyBucket.Arn

Todos:

• Write tests
• Write documentation
• Fix linting errors
• Make sure code coverage hasn't dropped
• Provide verification config / commands / resources
• Enable "Allow edits from maintainers" for this PR
• Update the messages below

Is this ready for review?: YES
Is it a breaking change?: NO

[horike37]

Thank you for this @laardee 👍
Imo, this is AWS provider specific feature so it would be better to put those code under serverless/lib/plugins/aws/, otherwise this may introduce any side effect to the other providers.

What do you think?

[laardee]

@horike37 yes, that subset of shorthand tags is AWS specific. These tags need to be specified on the first YAML.load, where the schema is passed to the js-yaml. What could be done is that the schema creation would be in e.g. lib/plugins/aws/lib/cloudformation-schema.js, and it would be used in the lib/utils/fs/parse.js only if the contents of the file has /name:\s+aws/ (or some better regexp) <- that needs to be checked before YAML.load which parses the buffer to the object.

Edit: The /name:\s+aws/ regexp doesn't work, because if there are external files that need to be parsed, those don't have that.

One option could be first to try to parse the file without CloudFormation schema, if that throws YAMLException, then try to parse with CloudFormation schema, if that throws error, then try to parse with some other provider schema (if available), and so on. If the last try still errors, that will be thrown then, else the parsed data is returned.

[horike37]

@laardee

One option could be first to try to parse the file without CloudFormation schema, if that throws YAMLException, then try to parse with CloudFormation schema, if that throws error, then try to parse with some other provider schema (if available), and so on. If the last try still errors, that will be thrown then, else the parsed data is returned.

Thank you for the explanation 👍 Understood what you stated.
I think this is a best plan to me so far.
LGTM.