Post-merge hook for lockfile sync with pre-check on file changes to a…

…void unnecessary overhead

Fixes astral-sh#17

.gitignore

@@ -1,3 +1,4 @@
 __pycache__
 *.pyc
 .venv
+*.egg-info

.pre-commit-hooks.yaml

@@ -28,3 +28,16 @@
   pass_filenames: false
   additional_dependencies: []
   minimum_pre_commit_version: "2.9.2"
+- id: uv-sync
+  name: uv-sync
+  description: "Automatically run 'uv sync' on your repository after a checkout, pull or rebase"
+  entry: uv-sync-hook
+  args:
+    - "--locked"
+  language: python
+  always_run: true
+  pass_filenames: false
+  minimum_pre_commit_version: "2.9.2"
+  stages:
+    - post-checkout
+    - post-merge

README.md

@@ -88,6 +88,42 @@ To export to an alternative file, modify the `args`:
       args: ["--frozen", "--output-file=requirements-custom.txt"]
 ```
 
+To synchronize your dependencies upon branch checkout or pull:
+
+```yaml
+default_install_hook_types:
+  - pre-commit
+  - post-checkout
+  - post-merge
+  - post-rewrite
+default_stages:
+  - pre-commit
+- repo: https://github.com/astral-sh/uv-pre-commit
+  # uv version.
+  rev: 0.5
+  hooks:
+    - id: uv-sync
+```
+
+To synchronize all dependencies in a workspace.
+The hook assumes the lock file is properly generated and will not look up for nested files. 
+
+```yaml
+default_install_hook_types:
+  - pre-commit
+  - post-checkout
+  - post-merge
+  - post-rewrite
+default_stages:
+  - pre-commit
+- repo: https://github.com/astral-sh/uv-pre-commit
+  # uv version.
+  rev: 0.5
+  hooks:
+    - id: uv-sync
+      args: ["--frozen,"--all-packages"]
+```
+
 ## License
 
 uv-pre-commit is licensed under either of

hooks/uvsync.py

@@ -0,0 +1,62 @@
+"""
+UV sync hook
+
+Should run as post-merge, post-checkout or post-rewrite hook
+Detect dependency changes from previous commit and run uv sync if necessary
+"""
+
+import os
+import subprocess
+import sys
+
+GIT_DIFF_CMD = ["git", "diff", "--quiet"]
+UV_FILES = ["pyproject.toml", "uv.lock", "uv.toml"]
+
+def git_diff(from_ref: str, to_ref: str) -> subprocess.CompletedProcess:
+    """
+    Run git diff --quiet from_ref to_ref -- pyproject.toml uv.lock uv.toml
+    Return code 0 means no changes, 1 means changes
+    """
+    return subprocess.run([*GIT_DIFF_CMD, from_ref, to_ref, "--", *UV_FILES])
+
+
+def detect_lock_changes() -> bool:
+    """
+    According to [documentation](https://pre-commit.com/#post-checkout),
+    post-checkout hook receives 3 environment variables:
+    PRE_COMMIT_FROM_REF, PRE_COMMIT_TO_REF, PRE_COMMIT_CHECKOUT_TYPE
+    As obscure as is the third one, we refer to [git documentation](https://git-scm.com/docs/githooks#_post_checkout)
+    and know its value is 1 for branch checkout and 0 for file checkout.
+
+    The post-merge hook receives 1 environment variable:
+    PRE_COMMIT_IS_SQUASH_MERGE: a flag indicating whether the merge is a squash merge or not.
+    We don't care about it, we'll just use it to detect post-merge hook.
+
+    The post-rewrite hook receives 1 environment variable:
+    PRE_COMMIT_REWRITE_COMMAND: a flag indicating the rewrite command, it can be rebase or amend.
+    """
+
+    # Scenario 1: post-checkout branch
+    # only branch checkout is relevant
+    # PRE_COMMIT_FROM_REF and PRE_COMMIT_TO_REF differ
+    if (from_ref := os.getenv("PRE_COMMIT_FROM_REF")) != (
+        to_ref := os.getenv("PRE_COMMIT_TO_REF")
+    ):
+        return git_diff(from_ref, to_ref).returncode == 1
+
+    # Scenario 2: post-merge
+    # Whatever PRE_COMMIT_IS_SQUASH_MERGE is, we need to compare the current HEAD with its parent
+    if "PRE_COMMIT_IS_SQUASH_MERGE" in os.environ:
+        return git_diff("HEAD^", "HEAD").returncode == 1
+
+    # Scenario 3: post-rewrite
+    if os.getenv("PRE_COMMIT_REWRITE_COMMAND") == "rebase":
+        return git_diff("ORIG_HEAD", "HEAD").returncode == 1
+
+def main():
+    if detect_lock_changes():
+        os.execvp("uv", ["uv", "sync", *sys.argv[1:]])
+
+
+if __name__ == "__main__":
+    main()

pyproject.toml

@@ -1,10 +1,18 @@
 [project]
 name = "uv-pre-commit"
 version = "0.0.0"
+requires-python = ">=3.11"
 dependencies = [
     "uv==0.5.1",
 ]
 
+[build-system]
+requires = ["setuptools>=61.0"]
+build-backend = "setuptools.build_meta"
+
+[project.scripts]
+uv-sync-hook = "hooks:uvsync.main"
+
 [project.optional-dependencies]
 dev = [
     "packaging~=23.1",