Types broken for TypeScript < 3

[mockdeep]

When we upgraded immutability-helper to version 2.9.0, our TypeScript build broke with the following error:

node_modules/immutability-helper/index.d.ts:25:57 - error TS1110: Type expected.

25     $splice: Array<[number, number?] | [number, number, ...T[]]>;
                                                           ~~~

I'm wondering if this is a syntax that is was added in TypeScript 3, as we're still on 2.8.3.

[jednano]

That is a new syntax, yes. 2.8.3 is pretty far behind. Have you talked about upgrading? @kolodny it looks like the release was not backwards compatible for TS projects < v3. Maybe we can backport a fix and bump the version of this package to a major?

[mockdeep]

@jedmao Yeah, we'd like to upgrade, but when we last tried it turned out to be a complicated mess with Webpack and other dependencies, so we shelved it until we've got more time for it. TS3 was released less than 6 months ago, so it seems like 2.8 might still be in the support window for most libraries.

[kolodny]

Is there some way to provide different typings for older TS versions? If there is then we can just use the pre typescript versions since those seemed to work fine

[jednano]

Yeah we can tell people to lock their versions and all, but it doesn't change the fact that this "minor" version bump just broke something.

[kolodny]

Hmm, in that case, I'd suggest reverting the last change and publishing another minor version and then republishing the current as a major version bump

[jednano]

Need to publish a new "patch" version, not a minor version, so 2.9.1 will have the fix and then 3.0 will be really the same as 2.9.0.

[jednano]

It might even make sense to create a 2.x branch and publish off of that with the revert so you don't have to change master and then subsequent updates can just go on master and fixes can go on the older 2.x branch.

[mockdeep]

Unfortunately, I don't know that that really helps us. If it's about needing to lock to a version, we can do that now. The ideal for us would be that we could continue to upgrade immutability-helper independent of TypeScript, at least for a while longer. I guess there's no hard and fast rule for how long to maintain backwards compatibility, but for something as widely used as TypeScript, it seems like that window should be on the order of 9 months or more for a major version bump.

It's not a big deal, but we do try to keep the bulk of our libraries up to date. So far, this is the first library we've run into that needs to be locked due to TS support, aside from the direct TS dependencies.

[kolodny]

The 2.x branch should now be safe for ts@2 users. Closing for now since there isn't much else to do for this. Feel free to reopen is your issues can be further addressed. Thanks!