Convert all the things to Typescript

[cellog]

This is an incremental step. It converts the existing source to use Typescript, but using index.d.ts as the source for all types. I did it this way because the first branch I made had such extensive changes to the files, it assumed they were entirely new, and we lost the granular diffs this PR provides.

A follow-up PR would then begin extracting the types from index.d.ts gradually, until done, and then the last PR would be the configuration changes to tsconfig.ts in both / and tests/typescript. In / this will be turning on .d.ts generation, and in tests/typescript it will be changing the base to point at src instead of index.d.ts

This PR needs to be rebased after #3518 and #3519 are mergedEDIT: good to go!

[cellog]

ok @timdorr this is ready for review. If it is too complex, I'm happy to slice and dice to bring each file individually into typescript-land

[cellog]

@timdorr ping again, wondering how you'd like to proceed?

[timdorr]

Can we just do an export here since we're just shipping it back out? Actually, can't we do that for everything in this file? I'm guessing there's some silly Babel/Rollup + tree-shaking reason why not, but I figure I should ask :)

[cellog]

it's complicated - we will export them when merging index.d.ts into each file that it touches. For now, this is simplest.

[timdorr]

I think we can do this in a big-bang. I'm also OK with there being broken tests in the ts-conversion branch temporarily. As long as it doesn't end up on master in a broken state, we're all good.

[cellog]

I think we can do this in a big-bang. I'm also OK with there being broken tests in the ts-conversion branch temporarily. As long as it doesn't end up on master in a broken state, we're all good.

This PR has some issues - I've learned a bit about TS, so I'm splitting them out into separate ones

[timdorr]

To add some clarity: We can either remove workarounds for broken tests and leave them temporarily broken, or just annotate that something is a workaround that is to be replaced later (maybe as a // TODO comment with an eslint rule to fail those until removed).

Again, broken is fine while we're in-progress on this stuff.

[cellog]

To add some clarity: We can either remove workarounds for broken tests and leave them temporarily broken, or just annotate that something is a workaround that is to be replaced later (maybe as a // TODO comment with an eslint rule to fail those until removed).

Again, broken is fine while we're in-progress on this stuff.

I understand. However, because it is so difficult to debug broken types, I don't think it is as useful to break a whole bunch then try to fix them. I'm confident the work I'm doing now will be both correct and easier to evaluate.

[cellog]

closing in favor of the smaller PRs

[timdorr]

OK, I'm good with that approach too!