add initial flow typings for apollo-client

[jbaxleyiii]

I've added flow typings for the most commonly used API (I think I got all the critical bits of index.js) as well as updated the build script to package the typings in the npm bundle. This should mean that flow-typed and custom bindings are no longer needed for apollo-client.

TODO:

• Update CHANGELOG.md with your change

[stubailo]

Is there any way to test that these don't get out of date?

[jbaxleyiii]

@stubailo not without writing out tests in js instead of ts. However, I think I can break this file apart and put the files next to their source files under src. This may make it easier to keep up to date. I'll work on that tonight

[stubailo]

Could we maybe compile the tests, then run the compiled js tests with Flow and maybe catch some errors?

[helfer]

@jbaxleyiii I wouldn't break it apart. But it would be great if there was a way to check if the types are actually correct. For example, how do you know that there are no syntax errors in the flow types right now?

[jbaxleyiii]

@helfer flow has a way of writing tests for the types. I can do that instead and configure the CI to verify it 👍

[helfer]

That would be great!

[helfer]

Any update on this @jbaxleyiii?

[jbaxleyiii]

@helfer I didn't want to finish this until I new I would have some time to support the first couple releases in case there are issues with it.

I'm good to do that now so here are a few smoke tests and CI config!

[jbaxleyiii]

After this is released, I can release apollographql/react-apollo#695

Now off to merge PRs / close some issues!

[helfer]

This is awesome @jbaxleyiii! I'm going to merge it now, but I still have one question: how are we going to make sure that the flow types stay in sync with the source? Do we have to go in and update the flow types for every PR that we make if it changes a type or a signature? If so, that might be very cumbersome and error-prone, even if we add it as a task to the PR checklist.

[helfer]

Seems like I forgot to remove this in an earlier PR. Once I do remove it, how will we make sure that the flow typings stay updated? Is the only way to guarantee it to test every little thing?