[BUG] react/prop-types - false positive when returning null

[gcourtemanche]

I'm trying to update 7.20.0 to 7.20.3, but I have new false positive errors for components that can return null.

This is telling me 'number' is missing in props validationeslintreact/prop-types:

import React from 'react';

type Props = {
  number: number;
};

export default (props: Props) => {
  const { number } = props;

  if (number === 0) {
    return <p>Number is 0</p>;
  }

  return null;
};

But this is fine:

import React from 'react';

type Props = {
  number: number;
};

export default (props: Props) => {
  const { number } = props;

  if (number === 0) {
    return <p>Number is 0</p>;
  }

  return <p>Number is not 0</p>;
};

[ulrik59]

Same problem for me

[ljharb]

I assume that if you flip the first example so the null is returned conditionally and the jsx unconditionally, that it’ll be detected as a component properly?

[gcourtemanche]

@ljharb exactly, no issue if the null is returned in the condition

[ljharb]

Specifically, component detection should be looking at every return value, and if any of them are jsx, and if all of them are possibly valid component return values (jsx, null, or a string/number/array of those things), then it should be detected as a component. (cc @alexzherdev)

[hank121314]

Hi @gcourtemanche !
I have made a branch trying to resolved this problem.
Could you try this branch https://github.com/hank121314/eslint-plugin-react/tree/develop and test whether the issue is resolved?
Thanks!

[gcourtemanche]

Hi @hank121314, thanks for helping me with this issue. I tried running eslint using commit ad0bb3005640eb7f147916e6b524e61be2e71992 and I got this error:

Oops! Something went wrong! :(

ESLint: 7.3.1

TypeError: Cannot read property 'forEach' of undefined

[hank121314]

hmm, sorry for that.
Could you please give me your example code and which parser did you use?
Thanks!

[gcourtemanche]

With @typescript-eslint/parser, any file is throwing the error.

[hank121314]

If you don’t mind, could you please give me full error code?
And I need the file which occurred.
If any file is throwing the error, please give me an example code.
Like this.

Oops! Something went wrong! :(

ESLint: 7.3.1

TypeError: Cannot read property 'heritage' of undefined
Occurred while linting /Users/hankchen/Desktop/FrontEnd/Electron/electron-react-template/src/app/components/Charts/GaugeChart/GaugeChart.tsx:32← this file.
    at declarePropTypesForTSTypeAnnotation (/Users/hankchen/Desktop/FrontEnd/Electron/electron-react-template/node_modules/eslint-plugin-react/lib/util/propTypes.js:465:56)
    at markPropTypesAsDeclared (/Users/hankchen/Desktop/FrontEnd/Electron/electron-react-template/node_modules/eslint-plugin-react/lib/util/propTypes.js:677:33)
    at Object.markAnnotatedFunctionArgumentsAsDeclared (/Users/hankchen/Desktop/FrontEnd/Electron/electron-react-template/node_modules/eslint-plugin-react/lib/util/propTypes.js:720:7)
    at updatedRuleInstructions.<computed> (/Users/hankchen/Desktop/FrontEnd/Electron/electron-react-template/node_modules/eslint-plugin-react/lib/util/Components.js:914:43)
    at /Users/hankchen/.config/yarn/global/node_modules/eslint/lib/linter/safe-emitter.js:45:58
    at Array.forEach (<anonymous>)
    at Object.emit (/Users/hankchen/.config/yarn/global/node_modules/eslint/lib/linter/safe-emitter.js:45:38)
    at NodeEventGenerator.applySelector (/Users/hankchen/.config/yarn/global/node_modules/eslint/lib/linter/node-event-generator.js:254:26)
    at NodeEventGenerator.applySelectors (/Users/hankchen/.config/yarn/global/node_modules/eslint/lib/linter/node-event-generator.js:283:22)
    at NodeEventGenerator.enterNode (/Users/hankchen/.config/yarn/global/node_modules/eslint/lib/linter/node-event-generator.js:297:14)

If the occurred file is private you can mail to my email(hank121314@gmail.com).
Thanks you very much @gcourtemanche!

[hank121314]

Hi @gcourtemanche !
I think I might have found the issue related.
Did your repository have some syntax Intersection Types:
Like this:

type User = {
  user: string;
 }
// This line
type Props = User & {
  userId: string;
};

export default (props: Props) => {
  const { userId, user } = props;
  if (userId === 0) {
    return <p>userId is 0</p>;
  }
  return null;
 };

[gcourtemanche]

@hank121314 yes, it does have intersection types!

[hank121314]

The latest commit at developer branch solved intersection types issue! Please try it.
Thanks!

[gcourtemanche]

@hank121314 I can't find the developer branch :(

[hank121314]

Forget to tell I commit to my own fork. Here:https://github.com/hank121314/eslint-plugin-react/tree/develop

[gcourtemanche]

The error is gone but another error appeared:
propType "number" is not required, but has no corresponding defaultProps declaration. eslintreact/require-default-props

Using this code:

import React from 'react';

type Props = {
  number?: number;
};

export default (props: Props) => {
  const { number } = props;

  if (number === 0) {
    return <p>Number is 0</p>;
  }

  return null;
};

If I remove the optional to number, there is no error anymore.

[hank121314]

This error appeared because of rule(require-default-props).
Try to define defaultProps for react function component.
microsoft/TypeScript#31247

[gcourtemanche]

@hank121314 I only get the error when I'm using your branch

[hank121314]

The error should display.
The reasons why 7.20.3 won't display are:

1. 7.20.3 does not support TSTypeAliasDeclaration(like: type Props = { user: string; }) yet.(Fixed in my develop branch)
2. 7.20.3 will get some bug when conditionally return JSXElement.(Fixed in pr: [Fix]:prop-types: handle component returning null #2696)
   Running the code below, it should show the same error.

interface Props {
  number?: number;
};
export default (props: Props) => {
  const { number } = props;
  if (number === 0) {
    return null;
  }
  return <p>Number is 0</p>;
}

[gcourtemanche]

Great, thank you for you help @hank121314 ! :)

[hank121314]

Anytime 😄 .
I will make a pr after my latest pr is merged