libdefs: Fix/suppress most glossed-over errors in react-intl libdef

[chrisbobbe]

Like we did for React Nav's libdefs in #5263. This will help us toward the RN v0.65 upgrade, #5230, by preparing to upgrade Flow.

Done by temporarily upgrading to Flow v0.149, which has this bugfix from Flow v0.143—

• Previously, errors in library files were sometimes being missed due to a bug. This has been fixed, which may expose errors in library files that were not previously being reported.

—and going through the newly caught errors.

@gnprice, three of these errors remain after this branch. Would you be up for taking a stab at the best approach for them? You could add some commits if you see something easy, or else let me know a good direction and I'll do it. Thanks!

Error ---------------------------------------------------------------------------- flow-typed/react-intl_vx.x.x.js:64:36

Cannot resolve name `Pick`. [cannot-resolve-name]

   64|   declare var DEFAULT_INTL_CONFIG: Pick<
                                          ^^^^


Error --------------------------------------------------------------------------- flow-typed/react-intl_vx.x.x.js:173:43

Cannot resolve name `Exclude`. [cannot-resolve-name]

   173|   declare export type FormatDateOptions = Exclude<DateTimeFormatOptions, 'localeMatcher'> &
                                                  ^^^^^^^


Error --------------------------------------------------------------------------- flow-typed/react-intl_vx.x.x.js:780:37

Cannot resolve name `Omit`. [cannot-resolve-name]

   780|   declare type OptionalIntlConfig = Omit<IntlConfig, $Keys<typeof DEFAULT_INTL_CONFIG>> &
                                            ^^^^

Looks like they're uses of TypeScript's utility types with those names. (This libdef began from a TypeScript to Flow translation using Flowgen.) I am kind of puzzled by the uses of Exclude and I wonder if they really meant to be uses of Omit…

[gnprice]

Thanks! These changes all look good -- please merge at will.

I'm looking at those three remaining errors.

[gnprice]

For Pick, it looks like it's basically doing the same job as the SubsetProperties in our generics.js.

Sadly I'm not finding a way to implement a version with the same interface as Pick, where it takes a union of the keys. I hoped this might work:

type Pick<T, Keys> = SubsetProperties<T, { [Keys]: mixed }>;

but it doesn't (try-flow). And in retrospect that makes sense -- I think the issue is probably that $ObjMapi on an indexer like { ['a' | 'b']: mixed } is going to produce a type with a corresponding indexer, { ['a' | 'b']: /* something */ }, not an object type with separate property entries for a and b.

So the best available solution may instead be to copy in SubsetProperties, like declare type SubsetProperties…, and then edit each of the Pick<…> sites to use that instead.

[gnprice]

For Omit, I'm afraid it looks like the same story. Here I was more hopeful because this definition seems like it really should work:

type Omit<T, Keys> = $Rest<T, {| [Keys]: mixed |}>;

But it seems to become another victim of indexers just being kind of broken:

type Omit<T, Keys> = $Rest<T, {| [Keys]: mixed |}>;

type T = {| a: number, b: string |};

(x: Omit<T, 'b'>): {| a: empty |} => x; // error, good
(x: Omit<T, 'b'>): {| a: number |} => x; // BAD error

// What happens instead:
(x: Omit<T, 'b'>): {| a: number | void, b: string | void |} => x; // weird!
// or spelling that out:
(x: $Rest<T, {| ['b']: mixed |}>): {| a: number | void, b: string | void |} => x; // weird!

// It's fine if there's normal properties instead of an indexer:
(x: $Rest<T, {| b: mixed |}>): {| a: number |} => x;

(try-flow)

So there also, I think the best solution may be to edit each of the sites, here to use $Rest instead.

---

For one of them:

  declare type OptionalIntlConfig = Omit<IntlConfig, $Keys<typeof DEFAULT_INTL_CONFIG>> &
    $Rest<typeof DEFAULT_INTL_CONFIG, { ... }>;

I think one can also simplify by taking advantage of Flow's spreads to make the Omit unnecessary:

  declare type OptionalIntlConfig = { ...IntlConfig, ...$Rest<typeof DEFAULT_INTL_CONFIG, { ... }> };

[gnprice]

And then for Exclude, I agree that all of its uses appear to be mistakes where Omit was intended. (That can fairly be blamed on the TypeScript folks, perhaps -- those two names are basically synonyms and it's not at all clear how to say which one goes with which meaning.)

[chrisbobbe]

Thanks! These changes all look good -- please merge at will.

I'm looking at those three remaining errors.

Great, thanks! Merged, and I'll address the three remaining ones in a new PR.