Added support for serverless.json. Improved error messages with filename

[HyperBrain]

What did you implement:

Closes #3566

How did you implement it:

Service.load() now tries to find one of the supported service filename variants (serverless.yaml, serverless.yml and new serverless.json, with this precedence). As soon as one is found, it will be loaded. Additionally the filename is remembered and printed in the error messages. Previously some error .... in serverless.yml was printed regardless, if the file was named .yaml or .yml.

JSON service file support is added with no tech debt, as the used YAML parser is spec compliant (a JSON is itself a valid YAML per definition) and will load the JSON out-of-the-box.

How can we verify it:

Convert any existing service.yml to JSON using some tool. Start your favorite serverless command.
It should behave and load exactly as before.

Additionally you can do some tests with multiple service files (.yml, .yaml, .json) to test the precedence - although I regard this as an edge case caused by sloppy development. ;-)

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

[pmuens]

🙏 This is really nice! Love it.

There are just a few tests missing. After that it should be GTM. Thank you very much @HyperBrain 👍 💯

[pmuens]

Unit tests which check for all the possible file extensions should be added

[HyperBrain]

Yes, you're right. I will add them - also a precedence check would be beneficial.

[pmuens]

Thanks 👍 +1 for the precedence check!

[HyperBrain]

Tests added.

[pmuens]

Thanks for updating @HyperBrain 💪

I tested it and it turns out that there are other parts in the codebase which needed an update (otherwise Serverless won't generate a .serverless directory since the service path could not be determined).

I've pushed the changes with the tests for those pieces and tested it thoroughly with the following serverless files:

serverless.yml

service: service

provider:
  name: aws
  runtime: nodejs6.10

functions:
  hello:
    handler: handler.hello

serverless.yaml

service: service

provider:
  name: aws
  runtime: nodejs6.10

functions:
  hello:
    handler: handler.hello

serverless.json

{
  "service": "service",
  "provider": {
    "name": "aws",
    "runtime": "nodejs6.10"
  },
  "functions": {
    "hello": {
      "handler": "handler.hello"
    }
  }
}

Everything works as a charm 🌟

GTM from my side.

Waiting for @eahefnawy and @brianneisler feedback

[HyperBrain]

Oh, I missed these. Thanks :)

[pmuens]

Just gave this another spin today and added some documentation updates.

Everything works fine! Will merge once the build passes 🎉