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Upgrade libuv to 1.53.0 via the rescript-lang/luv fork - #8883

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@cknitt cknitt commented Oct 17, 2026 •

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Upgrades the libuv used by the OCaml rewatch from 1.48.0 to 1.53.0 by building Luv from the rescript-lang/luv fork (rescript-lang/luv#2).

  • The opam override in .github/opam-repository now provides luv.0.5.14+rescript.1, fetched from the fork by commit hash (2094c025, the merge commit of Upgrade libuv to 1.53.0 and test native watcher APIs luv#2). dune-project and rescript.opam pin that version.
  • The fork already contains the ARM64 musl -mno-outline-atomics fix, so the local patch is removed.
  • The fork keeps libuv as a git submodule, so the source is a git URL rather than a GitHub archive (archives omit submodules); opam's git fetch initializes it. A future fork change becomes +rescript.2 with a new hash.
  • The fork's only API change (Luv.File.Statfs reserved fields now read as zero) doesn't affect us: rewatch only uses FS_event, Loop, Timer, Handle and Error in native_watcher.ml.

Performance is unchanged: watch latency, watcher startup, idle CPU and clean builds measured the same as with libuv 1.48 (Linux only; macOS and Windows weren't measured).

No new tests: there's no observable behavior change, and the existing watch tests in the shared rewatch suite cover the watcher.

🤖 Generated with Claude Code

https://claude.ai/code/session_01Q9Q6perkzKBQQebDnVXAEK

cknitt and others added 2 commits October 17, 2026 07:40
The opam override for Luv now fetches commit 8c12b1a of rescript-lang/luv
(PR rescript-lang/luv#2) instead of patching the upstream 0.5.14 tarball.
The fork vendors libuv 1.53.0 instead of 1.48.0 and already carries the
ARM64 musl -mno-outline-atomics fix, so the local patch is gone. The
package is versioned 0.5.14+rescript.1 and dune-project/rescript.opam pin
that version.

Review: Why a git URL and not a release tarball? The fork keeps libuv as a
git submodule; GitHub archives omit submodules, while opam's git fetch
initializes them. The commit hash should move to the merge commit once
rescript-lang/luv#2 lands.

Review: Does the OCaml rewatch use any changed Luv API? Only FS_event,
Loop, Timer, Handle and Error (native_watcher.ml). The fork's API change
(statfs reserved fields read as zero) does not reach it.

Area: rewatch ci
Output: unchanged
Tests: none, because no observable behavior changes; the shared rewatch
 suite (113 checks, incl. watch mode), the rewatch-ocaml focused suite and
 scripts/test.js -ounit -build -mocha -docstrings pass on the new libuv
Measured: watch edit latency, median of 21 interleaved edits (basic
 fixture) 99 -> 100 ms, A/A control 98 ms; 400-directory fixture 98 -> 102
 ms, A/A control 100 ms; watch cold start, median of 7 (400 dirs) 213 ->
 211 ms, A/A 212 ms; idle watcher CPU over 20 s 70-90 ms for all; clean
 build (400 modules), median of 9, 180 -> 180 ms; linux-arm64 devcontainer
 under load, job tmp watch_ab.py and clean_ab.py
Signed-off-by: Christoph Knittel <ck@cca.io>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Q9Q6perkzKBQQebDnVXAEK
The Luv override now fetches 2094c025, the merge commit of
rescript-lang/luv#2 and the fork's master tip, instead of the PR head
8c12b1a. Both commits have the same tree (7acc6c6d), so the built sources
are identical.

Area: ci
Output: unchanged
Tests: none, because the fetched source tree is identical to the tested one
Signed-off-by: Christoph Knittel <ck@cca.io>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Q9Q6perkzKBQQebDnVXAEK
@cknitt
cknitt marked this pull request as ready for review October 17, 2026 07:40
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cknitt requested a review from fhammerschmidt October 17, 2026 07:42
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rescript

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@rescript/belt

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@rescript/linux-arm64

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@rescript/win32-x64

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commit: 20c7647

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