Add return type to rememo jsDoc type annotations

[adamziel]

What problem does this PR solve?

Right now, the createSelector function loses the selector type details:

const iReturnNumbers = createSelector(
	( stringArg: string ) => 123,
	() => []
);
const iShouldBeANumber = iReturnNumbers();
// iShouldBeANumber is of type `any`

This is a problem in Gutenberg which depends on this package. For example, see the following PR: WordPress/gutenberg#41235 (comment)

How does this PR propose to solve this problem?

Adding the following @return type annotation preserves the selector type signature:

 * @return {S} Memoized selector.

The above snippet now works as expected:

const iReturnNumbers = createSelector(
	( stringArg: string ) => 123,
	() => []
);
const iShouldBeANumber = iReturnNumbers();
// iShouldBeANumber is of type `number`

Test plan

This changes just the documentation string, there are no runtime changes to test. Eyeballing the changes and confirming the types are now resolved as in the above examples should suffice.

Caveat: this could be considered a breaking change for any projects using createSelector in TypeScript. After upgrading rememo to a patched version, the selectors will be of a different type, which could cause type errors. This could be addressed by releasing a new major point release.

cc @aduth @dmsnell

[aduth]

Hey @adamziel , thanks for submitting this. It was expected that the return type would have been inferred by the JSDoc cast in the function return statement, so rather odd that it's falling back to the any type.

rememo/rememo.js

Line 295 in 3743aea

return /** @type {S & EnhancedSelector} */ (callSelector);

Also, the return type isn't strictly the same type as the original function, since it also supports the clear and getDependants function properties. I believe Gutenberg uses both of these functions as well, so losing that type detail might cause other breakage.

I do see in the published package's .d.ts declaration that the return type is S & EnhancedSelector (see line 16), so it looks like TypeScript is at least picking up that much correctly from the JSDoc. Maybe it's something with the intersection?

Not sure if you'd be willing to take a look into this, otherwise I can plan to spend some more time tomorrow evening digging into it.

[aduth]

I'm having trouble reproducing the original issue. I created a CodeSandbox, but it appears to be picking up the return value just fine with the given example?

https://codesandbox.io/s/wonderful-wave-3qtrbi?file=/src/index.ts

[adamziel]

@aduth that's a great news! To close the loop here, I just merged your Gutenberg PR WordPress/gutenberg#41415. I won't be able to fully check whether the types do what we need them to until after the WordCamp EU, but all the signs seem to say that upgrading rememo to a newer version should do the trick so I'm going to close this PR now. Thank you once gain!

[aduth]

Cool, hope it all works for you. Have a great time at WordCamp!