Lazy load node_modules to speed up Flow when in dependency hell

[kumar303]

With recent versions of npm, node_module dependencies are flattened, which creates a massive amount of top-level directories that Flow descends into at startup. Could this be done lazily, right as the app under test tries to import something that Flow needs to analyze? I think this would also address #719

As an example of how npm flattening affects Flow, my package.json defines 38 dependencies but my node_modules folder has 700 top-level modules 🔥 . When I auto-generated ignore rules for these folders (#719 (comment)), the Flow server would start up twice as fast.

[Macil]

Related suggestion: #869.

[samwgoldman]

@kumar303 Are you running 0.22? As of that version, we no longer parse non-@flow files, so large node_modules directories should have a much better experience.

[kumar303]

oh wow, it is a big improvement in 0.22, thanks! Feel free to close this issue. Funny enough, my startup time is faster now without my auto-generated ignore rules (probably because it's not doing so much regex).

[calebmer]

Closing, but we will continue thinking about not typechecking files in node_modules 👍