eslint-plugin-makefmt

Format Makefiles and justfiles through ESLint with makefmt. Aligns assignments and line continuations, indents conditionals, and formats recipes as shell with the rules of shfmt. Justfiles get the same output as just --fmt.

CC=gcc
CFLAGS   :=-O2 -Wall

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

becomes

CC     = gcc
CFLAGS := -O2 -Wall

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

The formatter is written in Rust and runs inside ESLint as WebAssembly, so there is nothing else to install.

Install

npm install --save-dev eslint eslint-plugin-makefmt

Requires ESLint 9.7 or later with flat config.

Usage

// eslint.config.js
import makefmt from 'eslint-plugin-makefmt'

export default [...makefmt.configs.recommended]

Then run npx eslint . to check and npx eslint --fix . to format.

The recommended config lints these files with the makefmt/format rule:

| Language | Files | | -------- | ---------------------------------------------------------------- | | Makefile | Makefile, makefile, GNUmakefile, *.mk, *.mak, *.make | | justfile | justfile, Justfile, .justfile, *.just |

Custom setup

Pick the language and the files yourself:

import makefmt from 'eslint-plugin-makefmt'

export default [
  {
    files: ['**/*.makefile'],
    plugins: { makefmt },
    language: 'makefmt/makefile',
    rules: {
      'makefmt/format': ['error', { indentWidth: 4 }],
    },
  },
]

The plugin provides two languages, makefmt/makefile and makefmt/justfile, and one rule, makefmt/format. The rule reports files that are not formatted, and --fix formats them. Files that can't be formatted, such as a justfile with a syntax error, are reported with the error.

Rule options

| Option | Default | Description | | ------------------------ | ------- | --------------------------------------------------- | | alignAssignments | true | Align assignment operators of consecutive variables | | alignAcrossComments | false | Keep aligning across comment lines | | alignContinuations | true | Align trailing backslashes of continued lines | | formatRecipes | true | Format recipe lines as shell with shfmt's rules | | indentConditionals | true | Indent conditional blocks such as ifeq/ifdef | | indentWidth | 2 | Spaces per indentation level | | maxBlankLines | 1 | Most consecutive blank lines to keep | | trimTrailingWhitespace | false | Also trim trailing whitespace on assignment lines |

Make keeps trailing whitespace in a variable's value, so PORT := 2184 sets PORT to 2184 . makefmt leaves it alone unless you turn on trimming, which can change values that relied on it.

The options only apply to Makefiles. Justfiles always use the style of just --fmt.

Project config

A .makefmt.toml in the Makefile's folder or any parent folder takes precedence over the rule options, so ESLint, the CLI and the VS Code extension all produce the same output:

align_across_comments = false
align_assignments = true
align_continuations = true
format_recipes = true
indent_conditionals = true
indent_width = 4
max_blank_lines = 1
trim_trailing_whitespace = false

Missing keys use the defaults. Unknown keys are an error.

ESLint's --cache doesn't know about .makefmt.toml, so delete the cache file (.eslintcache by default) after changing it.

oxlint

oxlint can load this plugin through jsPlugins and validates the rule options, but it can't lint Makefiles or justfiles yet: its JS plugins only run on JavaScript and TypeScript files, and custom languages are not supported. Use ESLint, or the makefmt CLI, for these files.