React version "detect" is slow, particularly for no-unknown-property

[lencioni]

I've been timing and profiling ESLint runs at Airbnb and noticed that react/no-unknown-property is particularly slow for us when using the "detect" setting for React version.

When running ESLint using TIMING=1 on a directory that contains about 500 files to be linted in it, react/no-unknown-property shows up as taking about 1700ms.

Looking at the callstacks in the profiler, it seems that when this rule calls getStandardName for every JSXAttribute here, it will actually do all of the work to detect the React version every time to determine the correct set of DOM property names.

https://github.com/yannickcr/eslint-plugin-react/blob/ef9a51225e3d5f6cb7cbdc3ec0382ad49246034b/lib/rules/no-unknown-property.js#L275

By specifying the react version in our ESLint config, the no-unkown-property rule drops out of the top 10 slowest rules entirely, with the 10th slowest clocking in at 180ms.

I think it would be a good idea to cache the React version when using detect instead of looking it up every time here: https://github.com/yannickcr/eslint-plugin-react/blob/ef9a51225e3d5f6cb7cbdc3ec0382ad49246034b/lib/util/version.js#L17-L33

Would you be open to a PR that did this?

[lencioni]

In the meantime, I'm going to use this bit of config:

  settings: {
    react: {
      // "detect" is slow
      // https://github.com/yannickcr/eslint-plugin-react/issues/2671
      // eslint-disable-next-line global-require
      version: require('react').version,
    },
  },

[ljharb]

Caching it makes total sense.