Case sensitivity issues when running on Windows

[shawnboltz]

Summary

Hello,

I've found an edge case on Windows where if you navigate to a git repository using a different case than the actual directory name (because Windows is case-insensitive) before installing prek, then prek install records the case that you used when navigating rather than the actual case in the hook's --cd argument. When you then go to make a commit to the repository, it fails becasue prek does a case-sensitive prefix comparison between this path and the output of git rev-parse --show-toplevel, which always returns the canonical casing. Since Windows filesystems are case-insensitive but not case-preserving in std::env::current_dir(), these two paths don't match and the commit fails:

(derzug) PS C:\testparent\testrepo> git commit -m "First"
Running in workspace: `C:\testparent\testrepo`
error: Failed to collect files
  caused by: Workspace root `C:\testparent\testrepo` is not under git root `C:/TestParent/testrepo`
  caused by: prefix not found

Steps to reproduce:

1. Create a git repo under a mixed-case parent: mkdir C:\TestParent\testrepo
2. Navigate using wrong casing on the parent: cd C:\testparent\testrepo
3. Add a valid prek.toml and run prek install
4. Attempt git commit

During step 3, I noticed that a hint gets issued that suggests this behavior is semi-intentional?

prek installed at `.git\hooks\pre-commit` for workspace `C:\testparent\testrepo`

hint: this hook installed for `C:\testparent\testrepo` only; run `prek install` from `C:/TestParent/testrepo` to install for the entire repo.

Suggested fix:
Either canonicalize the path (via std::fs::canonicalize() or equivalent) before writing it into the hook at install time, or use a case-insensitive comparison at commit time on Windows.

Willing to submit a PR?

• Yes — I’m willing to open a PR to fix this.

Platform

Windows 11

Version

prek 0.3.6 (dd53c3d 2026-03-16)

.pre-commit-config.yaml

None

Log file

2026-03-21T19:53:36.614909Z DEBUG prek: 0.3.6 (dd53c3d71 2026-03-16)
2026-03-21T19:53:36.615059Z DEBUG Changing current directory to: `C:\testparent\testrepo`
2026-03-21T19:53:36.615181Z DEBUG Args: ["C:\\Users\\mshaw\\Dropbox\\Python\\derzug\\.venv\\Scripts\\prek.exe", "hook-impl", "--hook-dir", "C:/TestParent/testrepo/.git/hooks", "--script-version", "4", "--hook-type=pre-commit", "--cd=C:\\testparent\\testrepo", "--"]
2026-03-21T19:53:36.715216Z TRACE get_root: close time.busy=99.1ms time.idle=20.9µs
2026-03-21T19:53:36.715314Z DEBUG Git root: C:/TestParent/testrepo
2026-03-21T19:53:36.715490Z DEBUG Found workspace root at `C:\testparent\testrepo`
2026-03-21T19:53:36.715513Z DEBUG Found project root at ``
2026-03-21T19:53:36.715633Z DEBUG Loading project configuration path=prek.toml
2026-03-21T19:53:36.718198Z TRACE Executing `C:\Program Files\Git\mingw64\libexec\git-core\git.exe ls-files --unmerged`
2026-03-21T19:53:36.763660Z DEBUG Found workspace root at `C:\testparent\testrepo`
2026-03-21T19:53:36.763737Z TRACE Include selectors: ``
2026-03-21T19:53:36.763758Z TRACE Skip selectors: ``
2026-03-21T19:53:36.764189Z DEBUG discover{root="C:\\testparent\\testrepo" config=None refresh=false}: Performing fresh workspace discovery
2026-03-21T19:53:36.764348Z TRACE discover{root="C:\\testparent\\testrepo" config=None refresh=false}:list_submodules{git_root="C:/TestParent/testrepo"}: close time.busy=36.9µs time.idle=2.60µs
2026-03-21T19:53:36.774924Z DEBUG Loading project configuration path=prek.toml
2026-03-21T19:53:36.782687Z TRACE discover{root="C:\\testparent\\testrepo" config=None refresh=false}: close time.busy=18.6ms time.idle=4.90µs
2026-03-21T19:53:36.782832Z TRACE Executing `C:\Program Files\Git\mingw64\libexec\git-core\git.exe diff --exit-code --name-only -z C:\testparent\testrepo\prek.toml`
2026-03-21T19:53:36.851851Z TRACE Checking lock resource="store" path=C:\Users\mshaw\AppData\Local\prek\.lock
2026-03-21T19:53:36.851917Z DEBUG Acquired lock resource="store"
2026-03-21T19:53:36.857357Z TRACE No requires-python found in pyproject.toml hook=check-yaml
2026-03-21T19:53:36.860521Z DEBUG Hooks going to run: ["check-yaml"]
2026-03-21T19:53:36.863642Z TRACE Executing `\\?\C:\Users\mshaw\AppData\Local\prek\hooks\python-4n6l5rAirdyuG6svTYxC\Scripts\python.exe -I -c import sys, json
info = {
    "version": ".".join(map(str, sys.version_info[:3])),
    "base_exec_prefix": sys.base_exec_prefix,
}
print(json.dumps(info))
 [...]`
2026-03-21T19:53:36.987845Z DEBUG Found installed environment for hook `check-yaml` at `C:\Users\mshaw\AppData\Local\prek\hooks\python-4n6l5rAirdyuG6svTYxC`
2026-03-21T19:53:36.988706Z TRACE Released lock path=C:\Users\mshaw\AppData\Local\prek\.lock
2026-03-21T19:53:36.988783Z TRACE Executing `C:\Program Files\Git\mingw64\libexec\git-core\git.exe diff --diff-filter=A --name-only -z -- C:\testparent\testrepo`
2026-03-21T19:53:37.008005Z TRACE Executing `C:\Program Files\Git\mingw64\libexec\git-core\git.exe write-tree`
2026-03-21T19:53:37.026896Z TRACE Executing `C:\Program Files\Git\mingw64\libexec\git-core\git.exe diff-index --binary --exit-code a1c1d3ccbda68bebae55b0a759b1c4b0e634deff -- C:\testparent\testrepo`
2026-03-21T19:53:37.048273Z DEBUG Working tree is clean
2026-03-21T19:53:37.048346Z TRACE collect_files: close time.busy=10.3µs time.idle=2.60µs

[j178]

I can’t see what’s different, but I’m not able to reproduce the issue.

In my second step, even if I cd into a path with the wrong letter case, it automatically resolves to the correct casing:

PS C:\> mkdir C:\TestParent\testrepo

    Directory: C:\TestParent

Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
d----           2026/3/22    17:30                testrepo

PS C:\> cd C:\testparent\testrepo
PS C:\TestParent\testrepo> git init
Initialized empty Git repository in C:/TestParent/testrepo/.git/
PS C:\TestParent\testrepo> prek install
prek installed at `.git\hooks\pre-commit`
PS C:\TestParent\testrepo> prek sample-config -f
Written to `.pre-commit-config.yaml`
PS C:\TestParent\testrepo> git add .
PS C:\TestParent\testrepo> git commit -m 'First'
trim trailing whitespace.................................................Passed
fix end of files.........................................................Passed
check yaml...............................................................Passed
check for added large files..............................................Passed
[master (root-commit) 289e914] First
 1 file changed, 10 insertions(+)
 create mode 100644 .pre-commit-config.yaml

[shawnboltz]

Oh, that's my bad (sorry, it took a few iterations to get it right and in my haste I copied the wrong one). I left out a pretty critical step in my reproducible example. It only happens when you use a config file for installing, ex.:

prek.toml:

minimum_prek_version = "0.3.6"

[[repos]]
repo = "https://github.com/pre-commit/pre-commit-hooks"
rev = "v2.3.0"
hooks = [
  { id  = "check-yaml" },
]

Now if you install with prek install -f the resulting pre-commit hook is as follows:

#!/bin/sh
# File generated by prek: https://github.com/j178/prek
# ID: 182c10f181da4464a3eec51b83331688

HERE="$(cd "$(dirname "$0")" && pwd)"
PREK="C:\Users\mshaw\Dropbox\Python\derzug\.venv\Scripts\prek.exe"

# Check if the full path to prek is executable, otherwise fallback to PATH
if [ ! -x "$PREK" ]; then
    PREK="prek"
fi

exec "$PREK" hook-impl --hook-dir "$HERE" --script-version 4 --hook-type=pre-commit --cd="C:\testrepo" -- "$@"

The key difference is that this time around the last line has this --cd="C:\testrepo" which is what it checks the case on. Interestingly, when you just do prek install, the --cd is omitted.

[j178]

It’s probably related to the canonicalization of the CWD. But I still can’t figure out how to reproduce it.

Whenever I use the wrong casing, like C:\testparent\testrepo, it automatically gets canonicalized to the correct one. I’m guessing there might be some Windows setting that controls this, maybe something I can turn off?

Here’s what I tried:

PS D:\Projects\Rust\prek> mkdir C:\TestParent\testrepo

    Directory: C:\TestParent

Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
d----           2026/3/29    17:42                testrepo

PS D:\Projects\Rust\prek> cd C:\testparent\testrepo
PS C:\TestParent\testrepo> git init
Initialized empty Git repository in C:/TestParent/testrepo/.git/
PS C:\TestParent\testrepo> prek sample-config --format toml -f
Written to `prek.toml`
PS C:\TestParent\testrepo> prek install
prek installed at `.git\hooks\pre-commit`
PS C:\TestParent\testrepo> type .\.git\hooks\pre-commit
#!/bin/sh
# File generated by prek: https://github.com/j178/prek
# ID: 182c10f181da4464a3eec51b83331688

HERE="$(cd "$(dirname "$0")" && pwd)"
PREK="D:\Projects\Rust\prek\target\debug\prek.exe"

# Check if the full path to prek is executable, otherwise fallback to PATH
if [ ! -x "$PREK" ]; then
    PREK="prek"
fi

exec "$PREK" hook-impl --hook-dir "$HERE" --script-version 4 --hook-type=pre-commit -- "$@"

[shawnboltz]

The specific trigger for it is using the ‘-f’ flag on install: ‘prek install -f’, though it looks like that may have been unnecessary. On Mar 29, 2026, at 02:54, Jo ***@***.***> wrote:  [https://avatars.githubusercontent.com/u/10510431?s=20&v=4]j178 left a comment (j178/prek#1850)<#1850 (comment)> It’s probably related to the canonicalization of the CWD. But I still can’t figure out how to reproduce it. Whenever I use the wrong casing, like C:\testparent\testrepo, it automatically gets canonicalized to the correct one. I’m guessing there might be some Windows setting that controls this, maybe something I can turn off? Here’s what I tried: PS D:\Projects\Rust\prek> mkdir C:\TestParent\testrepo Directory: C:\TestParent Mode LastWriteTime Length Name ---- ------------- ------ ---- d---- 2026/3/29 17:42 testrepo PS D:\Projects\Rust\prek> cd C:\testparent\testrepo PS C:\TestParent\testrepo> git init Initialized empty Git repository in C:/TestParent/testrepo/.git/ PS C:\TestParent\testrepo> prek sample-config --format toml -f Written to `prek.toml` PS C:\TestParent\testrepo> prek install prek installed at `.git\hooks\pre-commit` PS C:\TestParent\testrepo> type .\.git\hooks\pre-commit #!/bin/sh # File generated by prek: https://github.com/j178/prek # ID: 182c10f181da4464a3eec51b83331688 HERE="$(cd "$(dirname "$0")" && pwd)" PREK="D:\Projects\Rust\prek\target\debug\prek.exe" # Check if the full path to prek is executable, otherwise fallback to PATH if [ ! -x "$PREK" ]; then PREK="prek" fi exec "$PREK" hook-impl --hook-dir "$HERE" --script-version 4 --hook-type=pre-commit -- "$@" — Reply to this email directly, view it on GitHub<#1850?email_source=notifications&email_token=ARQXFLUHHWYXJJBHTJ3RB2T4TDXDVA5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTIMJUHE4DCNZVHA42M4TFMFZW63VGMF2XI2DPOKSWK5TFNZ2KYZTPN52GK4S7MNWGSY3L#issuecomment-4149817589>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/ARQXFLTSVXP3XQIZNKPXP334TDXDVAVCNFSM6AAAAACW2H3GLCVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHM2DCNBZHAYTONJYHE>. You are receiving this because you authored the thread.Message ID: ***@***.***>

[j178]

No luck.

PS C:\> mkdir C:\TestParent\testrepo
New-Item: An item with the specified name C:\TestParent\testrepo already exists.
PS C:\> rm -Recurse -Force C:\TestParent\
PS C:\> mkdir C:\TestParent\testrepo

    Directory: C:\TestParent

Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
d----           2026/3/30    23:30                testrepo

PS C:\> cd c:\testparent\testrepo
PS C:\TestParent\testrepo> git init
Initialized empty Git repository in C:/TestParent/testrepo/.git/
PS C:\TestParent\testrepo> prek sample-config -f
Written to `.pre-commit-config.yaml`
PS C:\TestParent\testrepo> prek install -f
prek installed at `.git\hooks\pre-commit`
PS C:\TestParent\testrepo> type .\.git\hooks\pre-commit
#!/bin/sh
# File generated by prek: https://github.com/j178/prek
# ID: 182c10f181da4464a3eec51b83331688

HERE="$(cd "$(dirname "$0")" && pwd)"
PREK="E:\Scoop\apps\prek\current\prek.exe"

# Check if the full path to prek is executable, otherwise fallback to PATH
if [ ! -x "$PREK" ]; then
    PREK="prek"
fi

exec "$PREK" hook-impl --hook-dir "$HERE" --script-version 4 --hook-type=pre-commit -- "$@"