Added pre-commit hook

contrib/pre-commit-hook/install_pre_commit_hook.sh

@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+
+# This script installs the pre-commit hook, that checks whether staged files
+# are formatted according to rustfmt.toml
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd -P)"
+
+ROOT="$(git -C "$SCRIPT_DIR" rev-parse --show-toplevel 2>/dev/null)" || {
+  echo "install.sh: not inside a git repository" >&2
+  exit 1
+}
+
+SRC="$SCRIPT_DIR/pre-commit"
+DST="$ROOT/.git/hooks/pre-commit"
+
+cp -f "$SRC" "$DST"
+chmod +x "$DST"
+
+echo "Installed: $DST"

contrib/pre-commit-hook/pre-commit

@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+
+# This script has some limitations. Most notably, it checks the files on-disk, which is a problem
+# if a file was edited, added and then re-edited. The added (and thus to be committed) file is
+# different from the on-disk file. Furthermore, small differences between cargo ftm and rustfmt may exist.
+# As this is just a helpful tool, we can accept those limitations. 
+
+set -euo pipefail
+
+ROOT="$(git rev-parse --show-toplevel)"
+CFG="$ROOT/rustfmt.toml"
+
+git diff --cached --name-only -z --diff-filter=ACMR -- '*.rs' \
+  | xargs -0 -r rustfmt --config-path "$CFG" --check
+echo "rustfmt check successful"