WIP: reorder entries such that first registered entry is exported module

[knagaitsev]

The issue is explained here: webpack/webpack-dev-server#2692 (comment)

My idea is that the very first entry in the compilation should be the one that is exported, so that if a user or webpack-dev-server registers more entries later, those will not be exported when a user has a config like:

output: {
  library: 'main',
  libraryTarget: 'window'
},

This would result in a breaking change which I thinks make sense, but it can be adjusted if others find this to be a problematic breaking change. Consider the config:

entry: [
  './entry1.js',
  './entry2.js',
]

Current behavior: entry2.js is the exported module.

With my changes: entry1.js is the exported module (This seems more intuitive to me, feel free to disagree)

If we don't want this breaking change, then I can reorder the entry config again here:

webpack/lib/WebpackOptionsApply.js

Line 267 in 00634bb

compiler.hooks.entryOption.call(options.context, options.entry);

So that the last entry is the one exported.

What kind of change does this PR introduce?

fix (related to webpack-dev-server)

Did you add tests for your changes?

Not yet

Does this PR introduce a breaking change?

Yes, ordering of entries internally in webpack

What needs to be documented once your changes are merged?

How webpack entries work when exporting as a module

[webpack-bot]

For maintainers only:

• This needs to be documented (issue in webpack/webpack.js.org will be filed when merged)
• This needs to be backported to webpack 4 (issue will be created when merged)

[webpack-bot]

@Loonride The most important CI builds failed. This way your PR can't be merged.

Please take a look at the CI results from travis (failure) and appveyor (failure) and fix these issues.

[sokra]

I don't think this is the right fix for that.

• This mess up execution order
• It has always exported the last module, this would be a huge breaking change.
• Plugins can already control entry order, by applying the plugin before or after the plugins generated by the entry option.