[react] add tests for useState

[joehillen]

Add a test case to prevent this from happening again.

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• Use a meaningful title for the pull request. Include the name of the package modified.
• Test the change in your own code. (Compile and run.)
• Add or edit tests to reflect the change. (Run with npm test.)
• Follow the advice from the readme.
• Avoid common mistakes.
• Run npm run lint package-name (or tsc if no tslint.json is present).

[ferdaber]

So how does this pass here but not in the reported cases?

[typescript-bot]

@joehillen Thank you for submitting this PR!

🔔 @johnnyreilly @bbenezech @pzavolinsky @digiguru @ericanderson @DovydasNavickas @onigoetz @theruther4d @guilhermehubner @ferdaber @jrakotoharisoa @pascaloliv @Hotell @franklixuefei @Jessidhia @saranshkataria @lukyth @eps1lon - please review this PR in the next few days. Be sure to explicitly select Approve or Request Changes in the GitHub UI so I know what's going on.

If no reviewer appears after a week, a DefinitelyTyped maintainer will review the PR instead.

[joehillen]

@ferdaber Correct. Here is the test output if I revert your revert:

Error: /home/joe/src/DefinitelyTyped/types/react/test/hooks.tsx:217:15
ERROR: 217:15  expect  TypeScript@next compile error: 
Parameter 'r' implicitly has an 'any' type.
ERROR: 217:15  expect  TypeScript@next compile error: 
Argument of type '(r: any) => boolean' is not assignable to parameter of type 'boolean | ((prevState: false) => false) | ((prevState: true) => true)'.
  Type '(r: any) => boolean' is not assignable to type '(prevState: false) => false'.
    Type 'boolean' is not assignable to type 'false'.

    at /home/joe/src/DefinitelyTyped/node_modules/dtslint/bin/index.js:190:19
    at Generator.next (<anonymous>)
    at fulfilled (/home/joe/src/DefinitelyTyped/node_modules/dtslint/bin/index.js:5:58)
    at <anonymous>
error Command failed with exit code 1.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.

[typescript-bot]

👋 Hi there! I’ve run some quick performance metrics against master and your PR. This is still an experiment, so don’t panic if I say something crazy! I’m still learning how to interpret these metrics.

Let’s review the numbers, shall we?

Comparison details 📊

	master	#36338	diff
Batch compilation
Type count	53266	53298	+0.1%
Assignability cache size	23771	23799	+0.1%
Subtype cache size	3886	3889	+0.1%
Identity cache size	764	765	+0.1%
Language service
Samples taken	8788	2109	-76.0%
Identifiers in tests	2524	2532	+0.3%
getCompletionsAtPosition
Mean duration (ms)	401.8	376.3	-6.4%
Median duration (ms)	383.4	367.7	-4.1%
Mean CV		11.1%
Worst duration (ms)	853.0	839.8	-1.5%
Worst identifier	TransitionGroup	TransitionGroup
getQuickInfoAtPosition
Mean duration (ms)	414.2	388.5	-6.2%
Median duration (ms)	401.5	380.8	-5.2%
Mean CV		11.9%
Worst duration (ms)	836.9	773.3	-7.6%
Worst identifier	component	component
System information
Node version	v10.15.3	v10.15.3
CPU count	2	2
CPU speed	2.294 GHz	2.294 GHz
CPU model	Intel(R) Xeon(R) CPU E5-2673 v4 @ 2.30GHz	Intel(R) Xeon(R) CPU E5-2673 v4 @ 2.30GHz
CPU Architecture	x64	x64
Memory	6.8 GiB	6.8 GiB
Platform	linux	linux
Release	4.15.0-1041-azure	4.15.0-1045-azure

It looks like nothing changed too much. I’m pretty lenient since I’m still an experiment, so take a look anyways and make sure nothing looks out of place.

---

If you have any questions or comments about me, you can ping @andrewbranch. Have a nice day!

[DanielRosenwasser]

Is it effectively just a difference between versions? (CC @weswigham)

[joehillen]

I don't understand your question. Different versions of what?

…

On Fri, Jun 21, 2019, 01:14 Daniel Rosenwasser ***@***.***> wrote: Is it effectively just a difference between versions? (CC @weswigham <https://github.com/weswigham>) — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#36338?email_source=notifications&email_token=AABCBZBUGSQDF5NNBP4PNILP3SEX5A5CNFSM4H2GTMR2YY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGODYHY6AA#issuecomment-504336128>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AABCBZC2DTNSHT4ESH3MB3LP3SEX5ANCNFSM4H2GTMRQ> .

[joehillen]

To clarify, this test case is a common pattern in my React codebase and is what started returning an error when I updated @types/react and TS 3.5 yesterday. I suspect the error has to do with both the bad commit and the smarter type unions change introduced in 3.5.

What I think happened is (prevState: boolean) => boolean was widened to ((prevState: false) => false) | ((prevState: true) => true), which doesn't make sense because why would you ever call setState but not change the value.

Because it is such a common pattern in React, I thought it made an obvious test case.