pre-commit · damonbayer · Jun 16, 2026 · Jun 16, 2026 · Jun 16, 2026
diff --git a/pre_commit/languages/julia.py b/pre_commit/languages/julia.py
@@ -51,6 +51,13 @@ def get_env_patch(target_dir: str, version: str) -> PatchesT:
         ('JULIA_LOAD_PATH', target_dir),
         # May be set, remove it to not interfer with LOAD_PATH
         ('JULIA_PROJECT', UNSET),
+        # Keep the package depot inside the hook environment so installed
+        # packages and precompile caches persist with the env instead of
+        # leaking into a shared depot. The trailing separator leaves an empty
+        # entry, which julia expands to its default depots. This keeps the
+        # bundled stdlib resources (and their precompile caches) available so
+        # hooks don't recompile from scratch on first run.
+        ('JULIA_DEPOT_PATH', os.path.join(target_dir, 'depot') + os.pathsep),
     )
 
 

diff --git a/pre_commit/xargs.py b/pre_commit/xargs.py
@@ -28,7 +28,8 @@ def cpu_count() -> int:
         # On systems that support it, this will return a more accurate count of
         # usable CPUs for the current process, which will take into account
         # cgroup limits
-        return len(os.sched_getaffinity(0))
+        sched_getaffinity = getattr(os, 'sched_getaffinity')
+        return len(sched_getaffinity(0))
     except AttributeError:
         pass
 

diff --git a/tests/languages/julia_test.py b/tests/languages/julia_test.py
@@ -1,9 +1,12 @@
 from __future__ import annotations
 
 import os
-from unittest import mock
 
+from pre_commit import constants as C
+from pre_commit import lang_base
+from pre_commit.envcontext import envcontext
 from pre_commit.languages import julia
+from pre_commit.prefix import Prefix
 from testing.language_helpers import run_language
 from testing.util import cwd
 
@@ -31,15 +34,49 @@ def test_julia_hook(tmp_path):
     assert run_language(tmp_path, julia, 'src/main.jl') == expected
 
 
+def test_julia_hook_installs_into_env_local_depot(tmp_path):
+    code = """
+    using Example
+    println("Hello, world!")
+    """
+    _make_hook(tmp_path, code)
+
+    prefix = Prefix(str(tmp_path))
+    envdir = lang_base.environment_dir(
+        prefix, julia.ENVIRONMENT_DIR, C.DEFAULT,
+    )
+
+    # the depot julia points hooks at: first entry of its JULIA_DEPOT_PATH
+    patch = dict(julia.get_env_patch(envdir, C.DEFAULT))
+    julia_depot_path = patch['JULIA_DEPOT_PATH']
+    assert isinstance(julia_depot_path, str)
+    env_depot = julia_depot_path.split(os.pathsep)[0]
+    # it must live inside the per-hook env, not in a shared location
+    assert env_depot.startswith(envdir + os.sep)
+
+    # An ambient depot that the hook must ignore: get_env_patch overrides
+    # JULIA_DEPOT_PATH with the env-local depot so packages are installed there
+    # (and so persist with the hook env) rather than in a shared depot.
+    decoy_depot = os.path.join(str(tmp_path), 'decoy-depot')
+    with envcontext((('JULIA_DEPOT_PATH', decoy_depot + os.pathsep),)):
+        julia.install_environment(prefix, C.DEFAULT, ())
+
+    assert os.path.isdir(os.path.join(env_depot, 'packages', 'Example'))
+    decoy_example = os.path.join(decoy_depot, 'packages', 'Example')
+    assert not os.path.exists(decoy_example)
+
+
 def test_julia_hook_with_startup(tmp_path):
-    depot_path = tmp_path.joinpath('depot')
-    depot_path.joinpath('config').mkdir(parents=True)
-    startup = depot_path.joinpath('config', 'startup.jl')
-    startup.write_text('error("Startup file used!")\n')
-
-    depo_path_var = f'{depot_path}{os.pathsep}'
-    with mock.patch.dict(os.environ, {'JULIA_DEPOT_PATH': depo_path_var}):
-        test_julia_hook(tmp_path)
+    # a startup.jl in the active (env-local) depot must not be evaluated
+    envdir = lang_base.environment_dir(
+        Prefix(str(tmp_path)), julia.ENVIRONMENT_DIR, C.DEFAULT,
+    )
+    config_dir = os.path.join(envdir, 'depot', 'config')
+    os.makedirs(config_dir)
+    with open(os.path.join(config_dir, 'startup.jl'), 'w') as f:
+        f.write('error("Startup file used!")\n')
+
+    test_julia_hook(tmp_path)
 
 
 def test_julia_hook_manifest(tmp_path):