Fix Flow type ambiguity

[leebyron]

Fixes #1114

As reported in #1114, flow reports ambiguity when defining tests:

test('my test', t => {})

Flow will report that it could apply either the Test type or the Macro type. The Test type is an obvious fit, but Macro also applies since the ...args resolves to the empty array, and the optional title? attribute happens to be not provided.

My suggested fix is to merge the Test and Macro types together since Macro is really a superset of the Test type, and we don't lose any type safety by just expecting to always get Macros.

I tested this locally on a flow-typed repository and confirmed that the type ambiguity errors are solved.

[bookercodes]

Thanks for this, @leebyron!

Can't wait for this to be merged 🎆. In the meantime, is there a convinent way to apply this patch, do you know?

[bookercodes]

Hm. I tried to apply this locally but ran into some trouble. If anyone has any ideas, please let me know! Thanks!

[novemberborn]

My suggested fix is to merge the Test and Macro types together since Macro is really a superset of the Test type, and we don't lose any type safety by just expecting to always get Macros.

I haven't looked at (these, or any, really) Flow definitions much. From the test() method's perspective the t => {} function is a test implementation. "Macro" is more a way of explaining how to reuse test implementations, AVA doesn't care. Perhaps the types can be renamed Implementation rather than TestOrMacro?

Besides that, if Flow-users could try out this PR that'd be great. I don't really know how to test it myself.

[leebyron]

Great suggestion - I cleaned up the names of the types.

Anyone who would like to test this out locally, here's how I'm doing it:

• Clone AVA with this PR applied (https://github.com/leebyron/ava/tree/fix-flow-types) locally.
• From the directory you cloned to, run npm link to have npm use that as the source for ava.
• From your project that suffers from ava 0.17.0 with FlowType 0.35.0 results in type-ambiguity errors #1114, run npm link ava, then run flow check - you should no longer see flow complaining about AVA internals, and only see errors about your own code.
• (npm unlink)

[bookercodes]

@leebyron Ah, I guess you could say npm link was the missing... link. Gosh, I'm hilarious!

Jokes aside, I managed to apply your fix locally and things work smoothly in my project, thanks!

[sindresorhus]

Thanks for helping us out with this one @leebyron. We really appreciate it. No one on the team has much experience with Flow.

[leebyron]

Thanks for the merge. Feel free to shout my way if you ever need help with anything related to type definitions.