Move browsers to cross-tool config

[ai]

Hi. I moved browsers from Autoprefixer’s inner option to browserslist in package.json.

Reason

• Autoprefixer team recommends only package.browserslist as a way to set target browsers.
• package.browserslist is used in many different tools. It is used by autoprefixer, stylelint-no-unsupported-browser-features, eslint-plugin-compat, postcss-cssnext, postcss-preset-env, postcss-normalize. The most important, this config will be used in next babel-preset-env 7.0.
• It is used by autoprefixer-info CLI tool. This CLI tool is part of autoprefixer package, but didn’t work correctly without Browserslist config.
• This config is useful not only for tools. The new developer will have the single place to check target browsers in a new project.
• CSS-Tricks agree that Browserslist config is really good idea.

Test

1. Create a new project.
2. Check project’s package.json for browserslist key.

[Timer]

We need to confirm the effect this has on babel-preset-env and we'd still like a way to limit the directory-up search to stop at the project boundary (we don't want a config file in the user's home directory to be picked up).

[ai]

Only babel-preset-env 7.0 will support it. But we have several tools with Browserslist already. Should we enable it right now and on Babel 7 release it will be used for babel-preset-env,?

[ai]

@Timer how do you suggest to limit directory-up search?

We need a really safe way since Browserslist is used in Autoprefixer (and it is the only recommended way to set browsers) with 10 M users :(.

We can limit it with first directory with .git/ inside. Does it safe? Does it used in other projects with directory-up search?

What limit is used in .babelrc and .eslintrc search?

[Timer]

I'm not sure of the search depth, but we disable .babelrc and .eslintrc usage.
Do you think we could disable browserslist search and provide it explicitly instead (by reading it ourselves)?
I believe this is the better option. This way we could inject a good default value as well.

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If directory up search limit would be an option, I'd imagine you'd provide a path to stop at as a configuration variable.

[ai]

@Timer yeap, we can read browserslist queries from some specific place. I can change PR for this behavior. What place will the best? browserslist key in ./package.json or .browserslistrc config?

[Timer]

Hmm, probably strictly browserslist in package.json while not-ejected, once ejected it can revert to default behavior and read from .browserslistrc and via directory-up method.

[Timer]

Note how we remove code on eject:
https://github.com/facebookincubator/create-react-app/blob/12120f6f55b51f533f603acbaa46d6fb56ca840f/packages/react-scripts/config/webpack.config.dev.js#L164-L178

[gaearon]

Meh. I don't feel too strongly about upwards search here—doesn't seem that it will be as common a problem as Babel configs.

[gaearon]

Is this change backwards-compatible? What happens for existing users who don't have anything in package.json? Ideally I'd like it to use our current list in this case.

[gaearon]

I started a branch for 2.0, getting it in. This is a breaking change because existing projects will need to add browserslist to avoid the new defaults (which now match BL's own defaults).

[frederikhors]

@gaearon @ai is this still valid for 2?

[ai]

Yeap, but not for Babel.

@gaearon maybe we should explain it more clear in changelog? With a link to Browserslist docs. Not a first-time people asking.

[gaearon]

I'll add it to the final release documentation checklist.