Fix install-hooks.bash script

I hadn’t realized there were Git hooks, but noticed them when I was
adding the Weeder script.

So, I documented that they exist, and then fixed the script since it
wasn’t working for me.

It now works
- when run it from anywhere in the repo (not just from two directories
  down somewhere),
- when `core.hooksPath` is set (i.e., `$GIT_DIR/hooks` isn’t the right
  place),
- when run from a worktree (which doesn’t necessarily have its own hooks
  dir),
- when the hooks directory doesn’t exist, and
- when the hooks already exist (if you pass `-f`).

This also replaces `ln -s` with `cp` so that in case the particular
worktree it was run from is renamed or deleted, it doesn’t break the
hooks for the repository.

Author: sellout

development.markdown

@@ -20,6 +20,14 @@ To get cracking with Unison:
 
 On startup, Unison prints a url for the codebase UI. If you did step 3 above, then visiting that URL in a browser will give you a nice interface to your codebase.
 
+## Git hooks
+
+There are some Git hooks provided by Unison. If you want to use them, you can run
+
+``` bash
+./scripts/install-hooks.bash
+```
+
 ## Autoformatting your code with Ormolu
 
 We use Ormolu (see [the specific version](./nix/versions.nix)) and CI will add an extra commit, if needed, to autoformat your code.

scripts/install-hooks.bash

@@ -1,9 +1,39 @@
 #!/usr/bin/env bash
+set -euo pipefail
+SCRIPTNAME="$(readlink -f -- "${BASH_SOURCE[0]}")"
+SCRIPTDIR="$(dirname -- "$SCRIPTNAME")"
 
-GIT_DIR=$(git rev-parse --git-dir)
+function usage {
+    echo "Usage: $SCRIPTNAME [-f] [-h]"
+    echo
+    echo "  -f   Overwrite hooks if they already exist"
+    echo "  -h   Show this usage message"
+}
+
+trap "echo; usage" ERR
+
+force=("-n")
+while getopts ':fh' OPTION; do
+    case "$OPTION" in
+        f)
+            force=("-f")
+            ;;
+        h)
+            usage
+            exit 0
+            ;;
+        \?)
+            usage
+            exit 1
+            ;;
+    esac
+done
+
+hooks_dir=$(git rev-parse --git-path hooks)
 
 echo "Installing hooks..."
+mkdir -p "$hooks_dir"
 # this command creates symlink to our pre-commit script
-ln -s ../../scripts/pre-commit.bash $GIT_DIR/hooks/pre-commit
-ln -s ../../scripts/pre-push.bash $GIT_DIR/hooks/pre-push
+cp "${force[@]}" "$SCRIPTDIR/pre-commit.bash" "$hooks_dir/pre-commit"
+cp "${force[@]}" "$SCRIPTDIR/pre-push.bash" "$hooks_dir/pre-push"
 echo "Done!"