Unable to setup environment for pre-commit hook run: unknown switch

[jerrygar96]

Hooks fail when trying to stash changes with message

Unable to setup environment for pre-commit hook run
STDOUT:
STDERR:error: unknown switch `0'
usage: git stash save [-p | --patch] [-S | --staged]...
stash message

in stash_changes in file stash_unstaged_changes.rb changing stash_message to use Time.now.to_i instead of Time.now seems to fix the issue for me.

This issue only presents itself when not committing all changed files.

[bwilde-castle]

I hit this same error and tracked down the root cause — it's a Windows-only quoting bug, not really about Time.now specifically.

Why this only happens on Windows: stash_changes passes the stash message as one array element straight to Subprocess.spawn. On macOS/Linux, ChildProcess.build(*args) executes that directly with no shell involved, so the message stays one atomic argument no matter what it contains. On Windows, though, Subprocess.spawn routes everything through win32_prepare_args, which wraps whitespace-containing args in quotes and then runs a metacharacter-escaping regex over the result — and that regex ([()%!^"<>&|]) also matches the quote marks it just added, corrupting them:

def win32_prepare_args(args)
  args = args.map do |arg|
    arg = "\"#{arg}\"" if arg =~ /\s/       # 1. wrap in quotes
    arg.gsub(/[()%!^"<>&|]/, '^\0')         # 2. re-escapes those same quotes, breaking them
  end
  %w[cmd.exe /c] + [args.join(' ')]
end

Once the quotes are corrupted, cmd.exe no longer treats the message as one quoted string and splits it on whitespace — so a stash message like ...at 2024-04-10 12:34:56 -0700 reaches git stash save with -0700 as a separate, bare argument, which git rejects. Repro:

require "overcommit/subprocess"
msg = "Overcommit: Stash of repo state before hook run at #{Time.now}"
Overcommit::Subprocess.send(:win32_prepare_args, ["git", "stash", "save", "--keep-index", "--quiet", msg]).last
# => "cmd.exe /c git stash save --keep-index --quiet ^\"Overcommit: ... -0700^\""

This affects any argument through Subprocess.spawn on Windows with a space plus a --prefixed token, not just this one call site — so switching to Time.now.to_i only dodges it here.

Suggested fix: drop the cmd.exe /c wrapper entirely for spawn/spawn_detached. Modern childprocess (5.1.0, tested) resolves .bat/.cmd shims fine via ChildProcess.build(*args) without it, and it handles .exe targets natively too. I verified this removes the bug end-to-end (real commits auto-stashing dirty files now succeed) without breaking bundle exec rspec/rubocop hooks that resolve to .bat shims.

Happy to open a PR if useful.