makefmt

A fast, safe Makefile and justfile formatter, for the command line, VS Code and ESLint.

VS Code Marketplace · Open VSX · npm · ESLint plugin

The formatter is written in Rust. The CLI ships as a native binary, and the VS Code extension and the ESLint plugin run the same code as WebAssembly, so format on save is instant.

CC=gcc
CFLAGS   :=-O2 -Wall
PREFIX?=/usr/local

SRCS = main.c \
	util.c \
      parser.c

ifeq ($(DEBUG),1)
CFLAGS += -g
endif

all:$(SRCS:.c=.o)   lib.a
	$(CC) $(CFLAGS) -o app $^

becomes

CC     = gcc
CFLAGS := -O2 -Wall
PREFIX ?= /usr/local

SRCS = main.c \
  util.c      \
  parser.c

ifeq ($(DEBUG),1)
  CFLAGS += -g
endif

all: $(SRCS:.c=.o) lib.a
	$(CC) $(CFLAGS) -o app $^

makefmt never changes what a working Makefile does. define bodies are left exactly as written, and anything it can't format safely stays as it is.

Recipes are formatted as shell with the rules of shfmt, as sh or, when SHELL is bash, as bash. With .ONESHELL, each recipe is formatted as one script, so if blocks and loops spread over several lines are indented too. Each formatted recipe is checked to hand the shell the same commands as before. Recipes for other shells, and any recipe that can't be formatted safely, are left as they are. Set format_recipes = false to leave all recipes alone.

A recipe line indented with spaces instead of a tab, which make rejects with missing separator or recipe commences before first target, is turned back into a recipe line.

The one thing it can't see is a .RECIPEPREFIX, SHELL or .ONESHELL set outside the file, in an included Makefile, on the command line or in the environment. Set them in the Makefile that uses them.

Justfiles get the same output as just --fmt, without needing just installed. makefmt contains a port of just's own parser and printer, and is tested against just 1.58.0.

A few rare cases differ from just --fmt: makefmt doesn't expand environment variables in x'...' strings while parsing, it rejects expressions nested more than about 1,000 levels deep, and in VS Code and ESLint it treats OS-specific settings such as [unix] set indentation as disabled.

Quick start

npx makefmt --write .

For VS Code, install the extension from the VS Code Marketplace, or from Open VSX for VSCodium, Cursor and Windsurf. It becomes the default formatter for Makefiles and justfiles, so Format Document and format on save just work.

For ESLint, see eslint-plugin-makefmt.

Runs on macOS (Apple Silicon and Intel), Linux (x64 and arm64) and Windows (x64).

Usage

makefmt [OPTIONS] [PATHS]...

With no paths, or -, makefmt formats stdin to stdout as a Makefile. Directories are searched for Makefiles (Makefile, makefile, GNUmakefile, *.mk, *.mak, *.make) and justfiles (justfile in any case, .justfile, *.just), skipping other hidden files and folders and anything in .gitignore.

| Option | Description | | ----------------------------------- | ------------------------------------------------------------------- | | -w, --write | Rewrite files in place | | --check | List unformatted files and exit with 1 if there are any | | --indent-width <N> | Spaces per indentation level (default 2) | | --max-blank-lines <N> | Most consecutive blank lines to keep (default 1) | | --align-across-comments <BOOL> | Keep aligning across comment lines (default false) | | --align-assignments <BOOL> | Align =, :=, ?=, += (default true) | | --align-continuations <BOOL> | Align trailing \ (default true) | | --format-recipes <BOOL> | Format recipe lines as shell (default true) | | --indent-conditionals <BOOL> | Indent ifeq/ifdef blocks (default true) | | --trim-trailing-whitespace <BOOL> | Also trim trailing whitespace on assignment lines (default false) | | --language <LANGUAGE> | Format stdin and named files as makefile or justfile |

Exit codes: 0 success, 1 --check found unformatted files, 2 error.

Configuration

Put a .makefmt.toml in your project. The CLI, the VS Code extension and the ESLint plugin all use the nearest one above the Makefile:

align_across_comments = false
align_assignments = true
align_continuations = true
format_recipes = true
indent_conditionals = true
indent_width = 2
max_blank_lines = 1
trim_trailing_whitespace = false

CLI flags override the file. In VS Code and ESLint, the file overrides the makefmt.* settings and rule options. These options only apply to Makefiles; justfiles always use the style of just --fmt. indent_width also sets the indentation inside recipes, where 0 means tabs.

Trailing whitespace is removed everywhere except on variable assignments, because make keeps it as part of the value: PORT := 2184 sets PORT to 2184 , so $(PORT)/db becomes 2184 /db. If that whitespace is never intended in your project, set trim_trailing_whitespace = true. Lines where trimming would change more than the value, such as one ending in \ , are still left alone.

Development

Requires Node.js, pnpm and Rust, plus the WebAssembly target: rustup target add wasm32-unknown-unknown.

pnpm install
pnpm build
pnpm lint
pnpm test

The tests compare against the real tools, so pnpm test needs just 1.58.0, shfmt 3.14.1 and GNU make 4.4 on PATH.

| Path | What it is | | -------------------- | ------------------------------------------------------ | | crates/core | The Makefile and justfile formatters | | crates/wasm | WebAssembly build of the formatter, shared by the apps | | apps/cli | The makefmt binary | | apps/vscode | The VS Code extension | | apps/eslint-plugin | eslint-plugin-makefmt | | scripts | Builds the npm package around the binaries |

pnpm --filter ./apps/vscode package builds apps/vscode/makefmt.vsix, which you can install with Extensions: Install from VSIX....

Releasing

Publish a GitHub release tagged vX.Y.Z. The workflow runs the tests, builds the binaries, publishes makefmt and eslint-plugin-makefmt to npm and the extension to the VS Code Marketplace and Open VSX, and attaches the binaries and the .vsix to the release. Pre-releases only go to npm, under the next tag.