Profile webpack to improve its watch performance

[fregante]

To enable faster development we'd want the watch step to finish as fast as possible after changing a file, but currently it often triggers the full rebuild (30s) instead of doing so incrementally.

Also:

• perf problems with require.context webpack/webpack#13636
  (but DEV_SLIM=true supposedly avoids this and saves ~5s on the first build)

A good start would be this command, but it produces hundreds of lines that need to be analyzed:

nr build:webpack -- --progress --profile --stats verbose

Related (they will likely improve performance as well):

• Messaging architecture webext-messenger#1
• Prevent context-specific code from being imported in the wrong context #669

[fregante]

I think there's no single thing slowing it down and likely no more "easy wins" are possible. The profiler output is enormous and it's probably not worth to look into — unless someone has deep webpack/plugins knowledge. Even looking at the flamegraph I don't see anything actionable.

Since watch speed is painfully visible during development, if I think of something I'll try it out, but for now I'll close this issue.

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Hopefully esbuild becomes an alternative at least during development, but it's not there yet:

• [MVP] Bundle CSS modules evanw/esbuild#20

At that point, even if it's not 1:1 with webpack’s results, it'd be a super-fast watcher and an alternative to DEV_SLIM, etc