ESLint Plugin: Add rule react-no-unsafe-timeout

[aduth]

This pull request seeks to introduce a new ESLint rule @wordpress/react-no-unsafe-timeout. In brief, it is meant to enforce the anti-pattern of setTimeout use in components which withSafeTimeout exists to address.

From the included rule documentation:

setTimeout in a component must be cancelled when the component is unmounted. This rule disallows references to the setTimeout global which occur in a component, and which are not assigned to a variable. A variable assignment is considered an acceptable use on the assumption that the timeout ID will be later referenced for cancellation via clearTimeout.

Consider using the withSafeTimeout higher-order component from the @wordpress/compose module.

In introducing the rule, it also resolves a few existing offending occurrences in code:

• packages/block-editor/src/components/rich-text/index.js
• packages/block-editor/src/components/url-input/index.js
• packages/components/src/form-token-field/suggestions-list.js

Testing Instructions:

Verify there are no errors when running npm run lint-js.

Verify unit tests pass running npm run test-unit

[gziolo]

Nice one, I'm starting to get comfortable with reviewing those ESLint rules. I like that all recent efforts are focused on preventing common mistakes rather than code style polishing 💯

[gziolo]

It still can be invalid (not canceled when the component gets unmount) but I think it's fine to assume good intents and keep implementation reasonable :)

[aduth]

It still can be invalid (not canceled when the component gets unmount) but I think it's fine to assume good intents and keep implementation reasonable :)

Right, the thinking was: You'd only ever care about the value produced by setTimeout if you intended to use it in clearTimeout (the return value is described as such). There's no guarantee here that this actually occurs, or that it occurs specifically in componentWillUnmount. But it's also the only option for considering "safe" in a generic sense where someone may want to use this rule, but wouldn't use withSafeTimeout from @wordpress/compose.

[nerrad]

@aduth - I'm curious, why is there no CHANGELOG.md entry for this new rule added?

[aduth]

@nerrad Oversight. I'll open a pull request shortly. Thanks for noting it.

[nerrad]

I figured :)