gofumpt

command module
Version: v0.3.1 Latest Latest
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Published: Mar 21, 2022 License: BSD-3-Clause Imports: 24 Imported by: 2

README

gofumpt

go install mvdan.cc/gofumpt@latest

Enforce a stricter format than gofmt, while being backwards compatible. That is, gofumpt is happy with a subset of the formats that gofmt is happy with.

The tool is a modified fork of gofmt as of Go 1.18. It can be used as a drop-in replacement to format your Go code, and running gofmt after gofumpt should produce no changes. For example:

gofumpt -l -w .

Some of the Go source files in this repository belong to the Go project. The added formatting rules are implemented in the format package.

Note that vendor directories are skipped unless given as explicit arguments. Similarly, the added rules do not apply to generated Go files unless they are given as explicit arguments.

Finally, note that the -r rewrite flag is removed in favor of gofmt -r, and the -s flag is hidden as it is always enabled.

Added rules

No empty lines following an assignment operator

example
func foo() {
    foo :=
        "bar"
}
func foo() {
	foo := "bar"
}

No empty lines around function bodies

example
func foo() {

	println("bar")

}
func foo() {
	println("bar")
}

Functions should separate ) { where the indentation helps readability

example
func foo(s string,
	i int) {
	println("bar")
}

// With an empty line it's slightly better, but still not great.
func bar(s string,
	i int) {

	println("bar")
}
func foo(s string,
	i int,
) {
	println("bar")
}

// With an empty line it's slightly better, but still not great.
func bar(s string,
	i int,
) {
	println("bar")
}

No empty lines around a lone statement (or comment) in a block

example
if err != nil {

	return err
}
if err != nil {
	return err
}

No empty lines before a simple error check

example
foo, err := processFoo()

if err != nil {
	return err
}
foo, err := processFoo()
if err != nil {
	return err
}

Composite literals should use newlines consistently

example
// A newline before or after an element requires newlines for the opening and
// closing braces.
var ints = []int{1, 2,
	3, 4}

// A newline between consecutive elements requires a newline between all
// elements.
var matrix = [][]int{
	{1},
	{2}, {
		3,
	},
}
var ints = []int{
	1, 2,
	3, 4,
}

var matrix = [][]int{
	{1},
	{2},
	{
		3,
	},
}

Empty field lists should use a single line

example
var V interface {
} = 3

type T struct {
}

func F(
)
var V interface{} = 3

type T struct{}

func F()

std imports must be in a separate group at the top

example
import (
	"foo.com/bar"

	"io"

	"io/ioutil"
)
import (
	"io"
	"io/ioutil"

	"foo.com/bar"
)

Short case clauses should take a single line

example
switch c {
case 'a', 'b',
	'c', 'd':
}
switch c {
case 'a', 'b', 'c', 'd':
}

Multiline top-level declarations must be separated by empty lines

example
func foo() {
	println("multiline foo")
}
func bar() {
	println("multiline bar")
}
func foo() {
	println("multiline foo")
}

func bar() {
	println("multiline bar")
}

Single var declarations should not be grouped with parentheses

example
var (
	foo = "bar"
)
var foo = "bar"

Contiguous top-level declarations should be grouped together

example
var nicer = "x"
var with = "y"
var alignment = "z"
var (
	nicer     = "x"
	with      = "y"
	alignment = "z"
)

Simple var-declaration statements should use short assignments

example
var s = "somestring"
s := "somestring"

The -s code simplification flag is enabled by default

example
var _ = [][]int{[]int{1}}
var _ = [][]int{{1}}

Octal integer literals should use the 0o prefix on modules using Go 1.13 and later

example
const perm = 0755
const perm = 0o755

Comments which aren't Go directives should start with a whitespace

example
//go:noinline

//Foo is awesome.
func Foo() {}
//go:noinline

// Foo is awesome.
func Foo() {}

Composite literals should not have leading or trailing empty lines

example
var _ = []string{

	"foo",

}

var _ = map[string]string{

	"foo": "bar",

}
var _ = []string{
	"foo",
}

var _ = map[string]string{
	"foo": "bar",
}

Field lists should not have leading or trailing empty lines

example
type Person interface {

	Name() string

	Age() int

}

type ZeroFields struct {

	// No fields are needed here.

}
type Person interface {
	Name() string

	Age() int
}

type ZeroFields struct {
	// No fields are needed here.
}
Extra rules behind -extra

Adjacent parameters with the same type should be grouped together

example
func Foo(bar string, baz string) {}
func Foo(bar, baz string) {}
Installation

gofumpt is a replacement for gofmt, so you can simply go install it as described at the top of this README and use it.

When using an IDE or editor with Go integration based on gopls, it's best to configure the editor to use the gofumpt support built into gopls.

The instructions below show how to set up gofumpt for some of the major editors out there.

Visual Studio Code

Enable the language server following the official docs, and then enable gopls's gofumpt option. Note that VS Code will complain about the gopls settings, but they will still work.

"go.useLanguageServer": true,
"gopls": {
	"formatting.gofumpt": true,
},
GoLand

GoLand doesn't use gopls so it should be configured to use gofumpt directly. Once gofumpt is installed, follow the steps below:

  • Open Settings (File > Settings)
  • Open the Tools section
  • Find the File Watchers sub-section
  • Click on the + on the right side to add a new file watcher
  • Choose Custom Template

When a window asks for settings, you can enter the following:

  • File Types: Select all .go files
  • Scope: Project Files
  • Program: Select your gofumpt executable
  • Arguments: -w $FilePath$
  • Output path to refresh: $FilePath$
  • Working directory: $ProjectFileDir$
  • Environment variables: GOROOT=$GOROOT$;GOPATH=$GOPATH$;PATH=$GoBinDirs$

To avoid unnecessary runs, you should disable all checkboxes in the Advanced section.

Vim-go

To configure gopls to use gofumpt:

let g:go_fmt_command="gopls"
let g:go_gopls_gofumpt=1
Govim

To configure gopls to use gofumpt:

call govim#config#Set("Gofumpt", 1)
Neovim

When using lspconfig, pass the gofumpt setting to gopls:

require('lspconfig').gopls.setup({
    settings = {
        gopls = {
            gofumpt = true
        }
    }
})
Emacs

For lsp-mode users on version 8.0.0 or higher:

(setq lsp-go-use-gofumpt t)

For users of lsp-mode before 8.0.0:

(lsp-register-custom-settings
 '(("gopls.gofumpt" t)))

For eglot users:

(setq-default eglot-workspace-configuration
 '((:gopls . ((gofumpt . t)))))
Sublime Text

With ST4, install the Sublime Text LSP extension according to the documentation, and enable gopls's gofumpt option in the LSP package settings, including setting lsp_format_on_save to true.

"lsp_format_on_save": true,
"clients":
{
	"gopls":
	{
		"enabled": true,
		"initializationOptions": {
			"gofumpt": true,
		}
	}
}
Roadmap

This tool is a place to experiment. In the long term, the features that work well might be proposed for gofmt itself.

The tool is also compatible with gofmt and is aimed to be stable, so you can rely on it for your code as long as you pin a version of it.

Frequently Asked Questions

Why attempt to replace gofmt instead of building on top of it?

Our design is to build on top of gofmt, and we'll never add rules which disagree with its formatting. So we extend gofmt rather than compete with it.

The tool is a modified copy of gofmt, for the purpose of allowing its use as a drop-in replacement in editors and scripts.

Why are my module imports being grouped with standard library imports?

Any import paths that don't start with a domain name like foo.com are effectively reserved by the Go toolchain. Third party modules should either start with a domain name, even a local one like foo.local, or use a reserved path prefix.

For backwards compatibility with modules set up before these rules were clear, gofumpt will treat any import path sharing a prefix with the current module path as third party. For example, if the current module is mycorp/mod1, then all import paths in mycorp/... will be considered third party.

How can I use gofumpt if I already use goimports to replace gofmt?

Most editors have replaced the goimports program with the same functionality provided by a language server like gopls. This mechanism is significantly faster and more powerful, since the language server has more information that is kept up to date, necessary to add missing imports.

As such, the general recommendation is to let your editor fix your imports - either via gopls, such as VSCode or vim-go, or via their own custom implementation, such as GoLand. Then follow the install instructions above to enable the use of gofumpt instead of gofmt.

If you want to avoid integrating with gopls, and are OK with the overhead of calling goimports from scratch on each save, you should be able to call both tools; for example, goimports file.go && gofumpt file.go.

Contributing

Issues and pull requests are welcome! Please open an issue to discuss a feature before sending a pull request.

We also use the #gofumpt channel over at the Gophers Slack to chat.

When reporting a formatting bug, insert a //gofumpt:diagnose comment. The comment will be rewritten to include useful debugging information. For instance:

$ cat f.go
package p

//gofumpt:diagnose
$ gofumpt f.go
package p

//gofumpt:diagnose v0.1.1-0.20211103104632-bdfa3b02e50a -lang=v1.16
License

Note that much of the code is copied from Go's gofmt command. You can tell which files originate from the Go repository from their copyright headers. Their license file is LICENSE.google.

gofumpt's original source files are also under the 3-clause BSD license, with the separate file LICENSE.

Documentation

The Go Gopher

There is no documentation for this package.

Directories

Path Synopsis
Package format exposes gofumpt's formatting in an API similar to go/format.
Package format exposes gofumpt's formatting in an API similar to go/format.
internal
diff
Package diff implements a Diff function that compare two inputs using the 'diff' tool.
Package diff implements a Diff function that compare two inputs using the 'diff' tool.

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