Canary: `MergeDeep` failures in `typescript@next` not detected by canary tests

[voxpelli]

I'm seeing a lot of these style of errors in the canary tests in my own modules:

Error: ../node_modules/read-pkg/node_modules/type-fest/source/merge-deep.d.ts(144,5): error TS2321: Excessive stack depth comparing types 'PickRestType<ArrayTail<ArrayTail<Destination>>>[number]' and 'UnknownArrayOrTuple'.
Error: ../node_modules/read-pkg/node_modules/type-fest/source/merge-deep.d.ts(144,5): error TS2321: Excessive stack depth comparing types 'PickRestType<ArrayTail<ArrayTail<Destination>>>[number]' and 'UnknownRecord'.
Error: ../node_modules/read-pkg/node_modules/type-fest/source/merge-deep.d.ts(144,5): error TS2321: Excessive stack depth comparing types 'PickRestType<ArrayTail<ArrayTail<Source>>>[number]' and 'UnknownArrayOrTuple'.
Error: ../node_modules/read-pkg/node_modules/type-fest/source/merge-deep.d.ts(170,5): error TS2321: Excessive stack depth comparing types 'PickRestType<ArrayTail<ArrayTail<Destination>>>[number]' and 'UnknownArrayOrTuple'.
Error: ../node_modules/read-pkg/node_modules/type-fest/source/merge-deep.d.ts(170,5): error TS2321: Excessive stack depth comparing types 'PickRestType<ArrayTail<ArrayTail<Destination>>>[number]' and 'UnknownRecord'.
Error: ../node_modules/read-pkg/node_modules/type-fest/source/merge-deep.d.ts(170,5): error TS2321: Excessive stack depth comparing types 'PickRestType<ArrayTail<ArrayTail<Source>>>[number]' and 'UnknownArrayOrTuple'.
Error: ../node_modules/read-pkg/node_modules/type-fest/source/merge-deep.d.ts(196,5): error TS2321: Excessive stack depth comparing types 'PickRestType<ArrayTail<ArrayTail<Destination>>>[number]' and 'UnknownArrayOrTuple'.
Error: ../node_modules/read-pkg/node_modules/type-fest/source/merge-deep.d.ts(196,5): error TS2321: Excessive stack depth comparing types 'PickRestType<ArrayTail<ArrayTail<Destination>>>[number]' and 'UnknownRecord'.
Error: ../node_modules/read-pkg/node_modules/type-fest/source/merge-deep.d.ts(196,5): error TS2321: Excessive stack depth comparing types 'PickRestType<ArrayTail<ArrayTail<Source>>>[number]' and 'UnknownArrayOrTuple'.

I didn't receive them in typescript@5.4.0-dev.20231119 then started receiving them in typescript@5.4.0-dev.20231121.

To avoid a regression once typescript@5.4.0 gets launched, we should track down the cause of this and file an issue with typescript if needed.

We should also track down why the canary tests in type-fest itself isn't catching it.

[voxpelli]

The regression should be caused by any of the following commits: microsoft/TypeScript@b4aefd2...13c9b16

Rather, as typescript@5.4.0-dev.20231120 seems to pass as well: microsoft/TypeScript@ffc21e5...13c9b16

[voxpelli]

Suggested to add type-fest into typescript's own canary tests: microsoft/typescript-error-deltas#129

[jakebailey]

FWIW you can pretty easily bisect this using every-ts: https://www.npmjs.com/package/every-ts

$ every-ts fetch
$ every-ts bisect bad 5.4.0-dev.20231121
$ every-ts bisect good 5.4.0-dev.20231119
$ every-ts tsc
$ every-ts bisect bad
$ every-ts tsc
$ every-ts bisect good
...

[voxpelli]

Finally got time to look into this and every-ts is really really great @jakebailey!

Came to the conclusion that its microsoft/TypeScript#56004 that caused these errors