Include Julia

[damonbayer]

Closes #307

Thanks for the very clear instructions on adding a new language!

Tagging @asottile for review

[asottile]

hi yes! I appreciate this I've been really busy recently -- do you think it would be possible to exercise julia in the test file? there's a few examples there that should be easy to follow. the rest looks pretty good though!

[damonbayer]

@asottile I had written tests but neglected to push them 😅

[damonbayer]

@asottile Have you had a chance to look at the test?

[asottile]

[damonbayer]

Hi @asottile, running into some problems running this on pre-commit.ci with this PR: https://results.pre-commit.ci/run/github/844767997/1780091363.7R9Koc3-QHSGllS_an0sJQ

Below is the result of my asking codex to investigate. It seems plausible, but you certainly would understand better than I would.

Codex investigation

It’s timing out during Julia package setup, before Runic ever runs.

I reproduced with the exact image family:

ghcr.io/pre-commit-ci/runner-image:2026-05-29-2c02030 is the minimal image and has no julia binary.
ghcr.io/pre-commit-ci/runner-image:2026-05-29-2c02030-full does have Julia 1.12.6.
With the -full image, a cold install of fredrikekre/runic-pre-commit@v2.2.0 took 111.5s here, and then the actual hook run took 1.2s.
pre-commit.ci’s build attempt timeout is 120s, so Runic’s first Julia Pkg.instantiate() / precompile path is right on the edge. On CI, with lazy image setup, network variance, or lower CPU, it crosses the 120s limit and gets killed at exactly the log line you showed:

[INFO] Installing environment for https://github.com/fredrikekre/runic-pre-commit.
[INFO] This may take a few minutes...
Interrupted (^C): KeyboardInterrupt

There’s a second wrinkle: runic-pre-commit@v2.2.0 declares language: julia and its entry is src/runic.jl; the script just does using Runic and calls Runic.main(...) (hook manifest, entrypoint). Its Project.toml only declares Runic as a dependency, with no checked-in Manifest.toml, so the first install has to resolve/download/precompile Julia packages.

So the failure is not that Runic is incompatible with the runner. It works once installed. The problem is that the cold Julia environment install is too slow for pre-commit.ci’s per-attempt build timeout. <aking it reliable on pre-commit.ci likely needs prewarming Julia/Runic package state in the image or otherwise reducing the cold Pkg.instantiate() cost.

[asottile]

yeah I mean if it's too slow to install then it's not really going to work

[damonbayer]

@asottile is it possible to go beyond the 120 sec limit for un-cached hooks? Julia is notoriously slow for "time to first plot" but is extremely quick after things have had a chance to pre-compile.

[ilia-kats]

For me it's still saying Executable julia not found.

[asottile]

@damonbayer there's an install timeout and a separate run timeout -- the one hit in your example above is the former

@ilia-kats that hook is language: system (the old name for language: unsupported ) and not language: julia