refactor: Tweak metro-file-map's Node crawler hot-path#1677
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A previous implementation kept a `visited` set in the Node crawler. Instead, we can also deduplicate and remove overlapping roots (directories within other roots) in the `FileMap` preemptively for all crawlers to prevent duplicate crawls.
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…ceNodeFilesystemAPI` flag) (#1693) Summary: This is a proposal to drop the native find binary crawler code path entirely. We've recently dropped the native find binary crawler in Expo, which was accidentally activated in some cases. We discovered (which is particularly obvious on large projects/repos and `expo/expo` itself) that it's consistently much slower than the Node FS crawler. To get into the "correct" preference and use the Node crawler, we're currently forcing `useWatchman: null`, which then defaults to use watchman, if it's installed, but falls back to `forceNodeFilesystemAPI: true`. This is outside of what the types specify as valid, but is the cleanest way to disable the native find binary crawling. This crawler basically just adds overhead over the Node.js implementation and is consistently slower, and less efficient, while the Node crawler is pretty optimised already (and has very low overhead once #1677 is merged) The timings of the native find binary crawler in `expo/expo` was also observed to scale with the size of this repo, compared to a minimal reproduction, so the overhead isn't just limited to the child process call and result parsing. Changelog: [Internal] Drop native find binary crawler and remove `forceNodeFilesystemAPI` flag Pull Request resolved: #1693 Test Plan: - Existing tests should pass - Quick generated script to play around with and assess the crawlers' comparative performance: kitten@74dffd4 Reviewed By: huntie Differential Revision: D101985455 Pulled By: robhogan fbshipit-source-id: efe2ab02fc5c0edac4d68f037db57c635fef8e50
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Summary
When a larger amount of paths are being crawled, the Node crawler becomes a hot-path and minor tweaks can have a larger impact on startup time, than previously anticipated (at least for Expo projects)
absoluteToNormalcalls (medium impact)forEachcalls for for-of (formatting only; virtually no impact)I don't currently have benchmarks for the above, and it's derived from running
apps/router-e2eonexpo/expo's main branch and modifyingmetro-file-map's Node crawler.Changelog: [Internal] Refactor performance sensitive Node crawler hot path in metro-file-map
Test plan