New: Add require-default-props rule (fixes #528)

[vitorbal]

Implements the new require-default-props rule. (#528)

This is a work in progress: support for flow annotations hasn't been added yet, but the code is already considerably big, so I thought I could get the PR up already to get some early feedback on implementation, docs, missing test cases, etc. flow annotation support has now been added.

This is my first time contributing to eslint-plugin-react, so I hope I didn't do something horribly wrong in the implementation of the rule 😟

[ljharb]

It would be great to have some tests that show that defaulting SFC arguments in the signature won't suffice; as well as updating the example documentation to explicitly describe why default arguments aren't the same as defaultProps

[vitorbal]

@ljharb thanks for the feedback! I've updated the docs to more explicitly mention that defaultProps are still preferred over default function params. Is this what you had in mind?

[ljharb]

Your changes look great, thanks!

[vitorbal]

Hope this is okay, sneaked in a fix for the wrong jsdoc for this function.

[vitorbal]

@ljharb @yannickcr alright, i pushed some new commits that add support for flow annotations to the rule. I tried to come up with the biggest number of test cases I could think of, but unfortunately I don't have any big repositories that use react and flow to test the rule against.

Are there any opensource projects that use both react and flow that we could test the rule against to catch some potential bugs? @ljharb is there any chance you could give the rule a test-drive at Airbnb?

[ljharb]

@vitorbal Airbnb does not yet use Flow; I don't have any projects I can test flow support on.

[vitorbal]

I added some extra tests for flow annotation use cases. Unfortunately I couldn't find any codebases using flow to test the rule on. However, I'm willing to react fast to any bugs found after this rule gets published, FWIW.

[yannickcr]

This is really great, thanks!