Make never rest type top-like

[Jack Williams (jack-williams)]

Not an actual fix as the issue is still under discussion. Figured I’d put up and implementation though.

Fixes#33495

[Jack Williams (jack-williams)]

TypeScript Bot (@typescript-bot) test this
TypeScript Bot (@typescript-bot) user test this

[TypeScript Bot (typescript-bot)]

Heya Jack Williams (@jack-williams), I've started to run the extended test suite on this PR at 76bc82b. You can monitor the build here. It should now contribute to this PR's status checks.

[TypeScript Bot (typescript-bot)]

Heya Jack Williams (@jack-williams), I've started to run the parallelized community code test suite on this PR at 76bc82b. You can monitor the build here. It should now contribute to this PR's status checks.

[TypeScript Bot (typescript-bot)]

The user suite test run you requested has finished and failed. I've opened a PR with the baseline diff from master.

[Wesley Wigham (weswigham)]

Makes a lot of sense to me - making never behave as any already did here seems to work. Can we also see a test for the nested case, eg

functionassignmentWithComplexRest2<Textendsany[]>(){constfn1: (cb: (x: string, ...rest: T)=>void)=>void=(cb)=>{};constfn2: (cb: (...args: never)=>void)=>void=fn1;}

which should error, I believe?

[Jack Williams (jack-williams)]

which should error, I believe?

Yep, added!

[Jack Williams (jack-williams)]

Thanks for powering through all these PR's Nathan Shively-Sanders (@sandersn) and Wesley Wigham (@weswigham)!

[Andrew Branch (andrewbranch)]

Was it known that this makes (...args: never) => unknown callable? #48840

[Jack Williams (jack-williams)]

Short answer: no. That function type should not be callable.

Longer answer: After looking through this again last night and trying to fix it, I do vaguely remember looking at that behaviour before. I think the code to trigger the error was move involved and touched a couple of the signature checking functions. I guess I never got around to resolving that and when the PR was revived, I had forgotten.

I started working on a fix yesterday. Haven't run it through perf and regression test. I do not think it is a big change. Also happy for someone to pick it up.

[Andrew Branch (andrewbranch)]

Thanks Jack Williams (@jack-williams), wasn’t expecting you to pick up a fix, just searching for info, but appreciate it!