Draft: Implement watching file paths via oslib.watch (for 0.12.x branch)
#5073
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arturaz
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lihaoyi
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May 8, 2025
lihaoyi
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lihaoyi
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Noticed this popping up while testing (note for self): |
…hing-0.12.x' into improvement/fs-watching-0.12.x
lihaoyi
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Currently watching files uses polling which is inefficient with large codebases. On my laptop `./mill --watch` uses 20% CPU just to watch the files for changes. This uses `oslib`'s `watch` module to watch for the file changes instead of polling them. We had to update oslib (com-lihaoyi/os-lib#386) to: - add a capability of filtering what folders it watches. This is needed because watching large generated folders like `out` or `.bloop` emits Java FS watcher `OVERFLOW` events. - remove the random `println`'s that `oslib.watch` had. The current approach to watching is to watch the workspace root via FS watching. FS watching only works with folders and we have to watch `root/build.mill`, and thus, `root/`, so everything else falls under it. Mac OS watcher performs watching recursively natively, but on linux oslib adds recursive watches itself, so we use `oslib.watch` filter to prevent watching anything that is not an ancestor of watched root. For example, if we have source at `root/module-a/src/`, we'll watch `root/`, `root/module-a/` and `root/`. Finally, events are filtered so that unrelated changes (like creating `root/random-file.txt`) does not trigger reevaluation. The fs watching is enabled by default and can be disabled via `--watch-via-fs-notify=false`. `0.12.x` version: #5073 --------- Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
…into improvement/fs-watching-0.12.x
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Backport of #5068
The fs watching is disabled by default and can be enabled via
--notify-watch=true.