port throw types PR from mmkal/ts#152 #14
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mmkal
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Oct 3, 2023
Fixes #17 Closes #36 (by documenting that `toMatchTypeOf` ~= `toExtend`) Closes #37 (by documenting that helper types are not part of the API surface) Closes #32 Closes #4 Closes #6 (by documenting that you _can't_ use `.not.toBeCallableWith(...)`) Closes #38 Use generics to give better error messages than "Arguments for the rest parameter 'MISMATCH' were not provided" for most `toEqualTypeOf` cases and many `toMatchTypeOf` cases. This trades off some implementation complexity for better end-user error messages. Essentially, write a special `<Expected extends ...>` constraint for each overload of each method, which does some crazy conditional logic, which boil down to: - `<Expected extends Actual>` for `toEqualTypeOf` (when we aren't in a `.not` context) - `<Expected extends Satisfies<Actual>>` for `toMatchTypeOf` Anyone interested, have a look at the snapshot updates in `errors.test.ts.snap` to see what the real world difference is. Each of these constraints apply only when we know it's going to "fail" - i.e. `Satisfies<...>` is a fairly meaningless helper type that is used to try to show errors at the type-constraint level rather than the `...MISMATCH: MismatchArgs<...>` level which won't give good error messages. When using `.not`, the constraint just becomes `extends unknown`, and you'll have to squint as before. See also: #14 for the better long-term solution, _if_ the TypeScript team decide to merge the throw types PR. See also: #13 for a hopefully-complementary improvement to the information on hover, which will improve the cases this doesn't cover. TODO: - [x] See if the `expectTypeOf({a: 1}).toMatchTypeOf({a: 'one'})` case can also be improved. - [x] Document. The constraints are a bit different to what most users would be used to, so it's worth highlighting the best way to read error messages and clarify when they might default to "Arguments for the rest parameter 'MISMATCH' were not provided" Note: I have publish v0.17.0-1 based on this PR and will hopefully be able to use [that version in vitest](vitest-dev/vitest#4206) as a test before merging.
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Closing, see comment:
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Update Oct 2023:
I'm going to close this since #16 improves error messages and the TypeScript PR was closed.
Copy-paste of mmkal/ts#152
Note - since this is a copy paste of a mod of an old version, a few features that have gone in since then may be regressed. This isn't going to go in anyway unless throw-types are added to TypeScript officially though.
original pr body
depends on microsoft/TypeScript#40468
Error messages before:
Error messages after:
