pre-commit hook to lint + fmt staged files with deno

pre-commit

#!/usr/bin/env bash

# pre-commit - deno fmt + deno lint
# ---------------------------------------------------------------------
# Copyright (c) 2025 Nicholas Berlette. All rights reserved.
# Published under the MIT License (https://nick.mit-license.org).
# ---------------------------------------------------------------------
# Runs deno's formatter and linter on staged files before committing.
#
# Place this file in your .git/hooks/ directory to enable pre-commit checks.
#
# Configuration options can be set using git config:
#
# ```gitconfig
# [hooks]
#   allownonascii = false        # Set to true to allow non-ASCII filenames
# [hooks "fmt"]
#   check    = true              # Set to false to auto-format staged files
#   disabled = false             # Set to true to disable formatting checks
#   patterns = ["*.ts", "*.js"]  # File patterns to format (overrides default)
# [hooks "lint"]
#   fix      = false             # Set to true to auto-fix linting issues
#   disabled = false             # Set to true to disable linting checks
#   patterns = ["*.ts", "*.js"]  # File patterns to lint (overrides default)
# [hooks "pre-commit"]
#   fmt  = "deno fmt --check"    # Command to run (or true / false)
#   lint = "deno lint"           # Command to run (or true / false)
# ```
#
# Note: The default settings of this hook require Deno to be installed, but
# you can easily customize the commands used for formatting and linting to
# adapt it to your project's needs.
#
# For example, to adapt this for a Rust codebase, these configs could be set:
#
# ```sh
# git config hooks.fmt.patterns "*.rs"
# git config hooks.lint.patterns "*.rs"
# git config hooks.pre-commit.fmt "cargo fmt -- --check"
# git config hooks.pre-commit.lint "cargo clippy -- -D warnings"
# ```

# An example hook script to verify what is about to be committed.
# Called by "git commit" with no arguments.  The hook should
# exit with non-zero status after issuing an appropriate message if
# it wants to stop the commit.
function verify_ascii() {
	if git rev-parse --verify HEAD >/dev/null 2>&1; then
		against=HEAD
	else
		# Initial commit: diff against an empty tree object
		against=$(git hash-object -t tree /dev/null)
	fi

	# If you want to allow non-ASCII filenames set this variable to true.
	allownonascii=$(git config --type=bool hooks.allownonascii)

	# Redirect output to stderr.
	exec 1>&2

	# Cross platform projects tend to avoid non-ASCII filenames; prevent
	# them from being added to the repository. We exploit the fact that the
	# printable range starts at the space character and ends with tilde.
	if [ "$allownonascii" != "true" ] &&
		# Note that the use of brackets around a tr range is ok here, (it's
		# even required, for portability to Solaris 10's /usr/bin/tr), since
		# the square bracket bytes happen to fall in the designated range.
		test $(git diff-index --cached --name-only --diff-filter=A -z $against |
			LC_ALL=C tr -d '[ -~]\0' | wc -c) != 0
	then
		cat <<-🔚
	Error: Attempt to add a non-ASCII file name.

	This can cause problems if you want to work with people on other platforms.

	To be portable it is advisable to rename the file.

	If you know what you are doing you can disable this check using:

		git config hooks.allownonascii true
🔚
		exit 1
	fi

	# If there are whitespace errors, print the offending file names and fail.
	exec git diff-index --check --cached $against --
}

DEFAULT_FMT_LINT_PATTERNS=("${DEFAULT_FMT_LINT_PATTERNS[@]:-}")

if [ "${#DEFAULT_FMT_LINT_PATTERNS[@]}" -eq 0 ]; then
	DEFAULT_FMT_LINT_PATTERNS=(
		'*.ts' '*.tsx' '*.mts' '*.cts'
		'*.js' '*.jsx' '*.mjs' '*.cjs'
		'*.json' '*.jsonc' '*.jsonl' '*.yaml' '*.yml' '*.toml' '*.md'
		'*.css' '*.scss' '*.sass' '*.less'
		'*.html' '*.njk' '*.vto' '*.hbs' '*.svelte' '*.astro' '*.vue'
		'*.ipynb' '*.sql'
	)
fi

function ensure_deno_installed() {
	if ! command -v deno >/dev/null 2>&1; then
	  export DENO_INSTALL="${DENO_INSTALL:-$HOME/.deno}"
		export PATH="$DENO_INSTALL/bin:$PATH"
		curl -fsSL https://deno.land/install.sh | sh
	fi

	if ! command -v deno >/dev/null 2>&1; then
		echo -n $'\e[1;31merror\e[0m Deno is not installed. Please install Deno to use this hook.\n' >&2
		exit 1
	fi
}

function fmt_staged() {
	# Run deno's formatter on staged files
	local disabled=$(git config --get --type bool hooks.fmt.disabled 2>/dev/null)
	[ "$disabled" -eq "true" ] && return 0

	local check=$(git config --get --type bool hooks.fmt.check 2>/dev/null || echo -n "true")
	[ "$check" -eq "false" ] && check=""

	local program=$(git config --get hooks.pre-commit.fmt 2>/dev/null || echo -n "true")
	[ "$program" -eq "false" ] && return 0
	[ "$program" -eq "true" ] && program="deno fmt${check:+ --check}"
	[[ "$program" == *"deno"* ]] && ensure_deno_installed

	local -a pats=($(git config --get-all hooks.fmt.patterns 2>/dev/null))
	if [ ${#pats[@]} -eq 0 ]; then
		pats=("${DEFAULT_FMT_LINT_PATTERNS[@]}")
	fi

	local -a files=($(git diff --cached --name-only -- "${pats[@]}"))
	if [ ${#files[@]} -ne 0 ]; then
		local message=$'\e[1;31merror\e[0m Formatting issues detected. Commit aborted!\n'
		if [[ "$check" == "true" ]]; then
			message+=$'\n\e[1;95mhint:\e[0m \e[3mtry setting\e[1;4:4;34;58;5;137mhooks.fmt.check\e[0;3m to \e[92m\'false\'\e[39m to auto-format before committing.\e[0m\n'
		fi

		$program "${files[@]}" >&2

		if [ $? -ne 0 ]; then
			echo -n "${message-}" >&2
			return 1
		fi

		# Re-add potentially modified files to the staging area
		git add "${files[@]}"
	fi
}

function lint_staged() {
	# Run deno's linter on staged files
	local disabled=$(git config --get --type bool hooks.lint.disabled 2>/dev/null || echo -n "false")
	[ "$disabled" -eq "true" ] && return 0

	local fix=$(git config --get --type bool hooks.lint.fix 2>/dev/null || echo -n "false")
	[ "$fix" -eq "false" ] && fix=""

	local program=$(git config --get hooks.pre-commit.lint 2>/dev/null || echo -n "true")
	[ "$program" -eq "false" ] && return 0
	[ "$program" -eq "true" ] && program="deno lint${fix:+ --fix}"
	[[ "$program" == *"deno"* ]] && ensure_deno_installed

	local -a pats=($(git config --get-all hooks.lint.patterns 2>/dev/null))
	if [ ${#pats[@]} -eq 0 ]; then
		pats=("${DEFAULT_FMT_LINT_PATTERNS[@]}")
	fi

	local -a files=($(git diff --cached --name-only -- "${pats[@]}"))
	if [ ${#files[@]} -ne 0 ]; then
		local message=$'\e[1;31merror\e[0m Linting issues detected. Commit aborted!\n'
		if [ -z "$fix" ]; then
			message+=$'\n\e[1;95mhint:\e[0m \e[3mtry setting\e[1;4:4;34;58;5;137mhooks.lint.fix\e[0;3m to \e[92m\'true\'\e[39m to enable auto-fixing.\e[0m\n'
		fi

		$program "${files[@]}" >&2

		if [ $? -ne 0 ]; then
			echo -n "${message-}" >&2
			return 1
		fi

		# Re-add potentially modified files to the staging area
		git add "${files[@]}"
	fi
}

verify_ascii && fmt_staged && lint_staged && exit 0
exit $?