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chore update TSTyche to v5#2172

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jdeniau merged 2 commits intoimmutable-js:mainfrom
mrazauskas:update-tstyche
Jan 22, 2026
Merged

chore update TSTyche to v5#2172
jdeniau merged 2 commits intoimmutable-js:mainfrom
mrazauskas:update-tstyche

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@mrazauskas mrazauskas commented Jan 9, 2026

Closes #2169

This PR updates TSTyche to v5.

TSTyche 4 release notes: https://tstyche.org/releases/tstyche-4
TSTyche 5 release notes: https://tstyche.org/releases/tstyche-5

Notable changes:

  • matcher .toBeAssignableWith() is renamed to .toBeAssignableFrom()
  • support for TypeScript 4.x is dropped

I think, these test cases look more consistent when .toBeAssignableTo() is used. Because the type under test stay on the left hand side in all assertions. Like Set([1, 'a']) in the following:

   expect(Set([1, 'a'])).type.toBe<Set<number | string>>();

-  expect<Set<number>>().type.not.toBeAssignableFrom(Set([1, 'a']));
+  expect(Set([1, 'a'])).type.not.toBeAssignableTo<Set<number>>();

This is sorted out. What about TypeScript version?

mrazauskas
mrazauskas commented Jan 9, 2026
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.github/workflows/ci.yml

- name: 'Test types'
run: npm run test:types -- --target 4.5,5.0,current
run: npm run test:types -- --target '5.0 || *'
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@mrazauskas mrazauskas Jan 9, 2026

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Since TSTyche 5, the syntax of a range has changed. As you see, now it is similar to semver range.

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mrazauskas commented Jan 10, 2026 •
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@jdeniau By the way, the following (from #2014) is now passing:

expect<Map<string, string>>().type.not.toBe<OrderedMap<string, string>>();

Unless I missed something, .sort() was the only method added to Map. So both interfaces still should be identical. This was puzzling. I think the return type this & OrderedMap<K, V> is the culprit. Well.. intersections or not well handled by TypeScript’s internal .isTypeIdenticalTo() method (it is utilised to compare types by TSTyche 5 and below).

The good news: TSTyche 6 does not use this internal method anymore. Patching is required, but that would not work with TypeScript 7 anymore.

I try to say that this PR could also update TSTyche to 6.0. The tests are passing. All works. Only detail to think about: minimum supported TypeScript version would be 5.4 (it is two years old and this is the lowest versions Definitely Typed is currently testing agains).

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jdeniau commented Jan 11, 2026

I will check that PR soon.
About dropping TS 5.3, maybe do that in the 6.x branch then (which main purpose in to drop decades of old code and support).

@jdeniau jdeniau merged commit 2481a77 into immutable-js:main Jan 22, 2026
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jdeniau commented Jan 22, 2026

thanks @mrazauskas !

I did merge that in main, and merged main in the 6.x branch, if you want to upgrade to tstyche 6.x

@mrazauskas mrazauskas deleted the update-tstyche branch February 2, 2026 09:03
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@mrazauskas @jdeniau