[Tabs][BottomNavigation] Use value over index property

[oliviertassinari]

This is an effort in the prolongation of #2957. I believe it's the last inconsistency we have in that dimension.

-<Tabs index={0}>
+<Tabs value={0}>
// ...

• PR has tests / docs demo, and is linted.
• Commit and PR titles begin with [ComponentName], and are in imperative form: "[Component] Fix leaky abstraction".
• Description explains the issue / use-case resolved, and auto-closes the related issue(s) (http://tr.im/vFqem).

[ljvanschie]

I don't know if this is the place to mention this, but the transition from index to value has not been implemented in the typings:

https://github.com/callemall/material-ui/blob/v1-beta/typings/index.d.ts#L1352

[oliviertassinari]

@sebald now you see why I think that automatic typescript generation is important. I have to admit, I haven't done any effort to keep the definitions up to date. But we can't expect external contributors to think about it. They already have to take into account the lint, flow-typed and test coverage.

[sebald]

@oliviertassinari Yes, that's what I am here for :)

I only can speak of personal experience, having typings of libs that are not written in TypeScript was never great. 1-2yrs it was actually pretty pretty bad. I still run into issues with typings on a weekly basis and have lots of custom typings or typings that overwrite bad/old typings from @types/*.

All I can say is that I "build" the typings in a way so that if anyone is running into troubles, they can easily overwrite certain typings. This is sadly not always they case.

Because I now know that you'll release over the weekend, I reserved myself a time slot at work to update typings on Friday. So my team can also update to the latest beta on Monday/Tuesday :)

If PRs get tagged as BREAKING CHANGE it should be possible to keep the typings up to date. If you think that the current approach doesn't work I can try to setup a POC using tsgen over the course of next week and we'll see if this work better :)

[oliviertassinari]

@sebald I won't say that the current approach doesn't work as we haven't had the opportunity to try it out yet. I would rather wait a month or two to see how that goes. At the end of the day, if your team is happy with the typescript coverage of the project we are good. The experiences from the rest of the community should be pretty close. This is a good proxy. If you think that tsgen can save us time and energie, go ahead otherwise don't :).