Add browserslist 4 support.

[yavorsky]

Q	A
Fixed Issues?	Fixes #8228
Patch: Bug Fix?
Major: Breaking Change?	Yes
Minor: New Feature?
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?	browserslsit > 4
License	MIT

After discussion with @ai and @existentialism and update browserslist to 4 we had an idea to possibly have targets as a query.
For now, browserslist 4 supports node. So in most cases, we don't need to use a plain object to specify targets directly. It's mostly confusing to have 2 sources of truth and merge this targets. For many people, it works like magic under the hood and it's not everytime clear why chrome: 55, browsers: 'chrome 40' will select chrome 55.
With browserslist 4 we just can specify every target we need using the query: targets: "node 8.1, last 2 chrome versions, maintained node versions".
Most of the people are using targets as a plain object just to support node version. This PR contains node current and current node versions which are being replaced to node ${currentNode} query.

So what was changed?

1. updated browserslist to 4 and added node.js mappings.
2. Allow targets to be as a query for browserslsit. (It's supposed that people won't use the object version in future and someday we could remove this functionality. Should be less confusing for users).
3. Don't search for browserslistconfig if targets field was specified. (Since browserslist support node) (breaking change).
4. support current node and node current queries, which is replaced with node ${CURRENT_VERSION}.

Would be good to merge it before babel 7, since it contains small breaking change (point 3).

cc @ai @existentialism

[ai]

Yeap, I highly recommend to include this PR to 7.0. People complained about the current behavior (merging targets and browserslist). And we will not be able to do it in next minor 7.x releases.

[ai]

Did you add current node to targets queries as the alias to last 1 node version? I can add this query to next Browserslist 4.1 release if Babel will use it.

[nicolo-ribaudo]

In case we don't merge this before Friday, would it be possible to remove (or workaround) the breaking change?

[ai]

@nicolo-ribaudo it is possible, but will be bad for users. Merging behavior is what is expected (and how other tools do it).

[ai]

I added current node query support to Browserslist master browserslist/browserslist@40b4816

Let’s remove node current since aliases are not common in Browserslist and we try to keep queries more English-ish.

Can release it just after you will approve the query.

[yavorsky]

Sounds awesome @ai

[existentialism]

Instead of modifying existing tests, should we just add new ones to make sure both syntaxes work (for now)?

[ai]

Browserlist 4.1 was released with current node query support for Babel

[chicoxyzzy]

Just my 2 cents: it will be breaking change for babel-preset-env, not Babel if we'll land it after Babel 7

[TrySound]

@chicoxyzzy babel preset env version is synchronised with all packages. So it will be a breaking change for all stuff.

[chicoxyzzy]

Actually it’s no so important to keep preset version in sync with Babel. More then that, this causes some issues. Also for example babel-loader and some other packages are not in sync with Babel version

[TrySound]

All packages in babel monorepo has the same version. babel-loader is part of it.
https://github.com/babel/babel/tree/master/packages

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/8893/

[existentialism]

@ai @TrySound bumped to 4.1!

[ai]

Should we remove ignoreUnknownVersions: true if we are using 4.1? (It was added to fix current nide hack for 4.0)

[existentialism]

@ai good point, will remove

[hzoo]

Ok looks good, I think the breaking change makes sense (targets shouldn't be related to browserslist)?

[ai]

Do we need something else to merge it?

Or just time for final decision