src/cmd/gofmt/doc.go

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

/*
Gofmt formats Go programs.
It uses tabs for indentation and blanks for alignment.
Alignment assumes that an editor is using a fixed-width font.

Without an explicit path, it processes the standard input.  Given a file,
it operates on that file; given a directory, it operates on all .go files in
that directory, recursively.  (Files starting with a period are ignored.)
By default, gofmt prints the reformatted sources to standard output.

Usage:

	gofmt [flags] [path ...]

The flags are:

	-d
		Do not print reformatted sources to standard output.
		If a file's formatting is different than gofmt's, print diffs
		to standard output.
	-e
		Print all (including spurious) errors.
	-l
		Do not print reformatted sources to standard output.
		If a file's formatting is different from gofmt's, print its name
		to standard output.
	-r rule
		Apply the rewrite rule to the source before reformatting.
	-s
		Try to simplify code (after applying the rewrite rule, if any).
	-w
		Do not print reformatted sources to standard output.
		If a file's formatting is different from gofmt's, overwrite it
		with gofmt's version. If an error occurred during overwriting,
		the original file is restored from an automatic backup.

Debugging support:

	-cpuprofile filename
		Write cpu profile to the specified file.

The rewrite rule specified with the -r flag must be a string of the form:

	pattern -> replacement

Both pattern and replacement must be valid Go expressions.
In the pattern, single-character lowercase identifiers serve as
wildcards matching arbitrary sub-expressions; those expressions
will be substituted for the same identifiers in the replacement.

When gofmt reads from standard input, it accepts either a full Go program
or a program fragment.  A program fragment must be a syntactically
valid declaration list, statement list, or expression.  When formatting
such a fragment, gofmt preserves leading indentation as well as leading
and trailing spaces, so that individual sections of a Go program can be
formatted by piping them through gofmt.

# Examples

To check files for unnecessary parentheses:

	gofmt -r '(a) -> a' -l *.go

To remove the parentheses:

	gofmt -r '(a) -> a' -w *.go

To convert the package tree from explicit slice upper bounds to implicit ones:

	gofmt -r 'α[β:len(α)] -> α[β:]' -w $GOROOT/src

# The simplify command

When invoked with -s gofmt will make the following source transformations where possible.

	An array, slice, or map composite literal of the form:
		[]T{T{}, T{}}
	will be simplified to:
		[]T{{}, {}}

	A slice expression of the form:
		s[a:len(s)]
	will be simplified to:
		s[a:]

	A range of the form:
		for x, _ = range v {...}
	will be simplified to:
		for x = range v {...}

	A range of the form:
		for _ = range v {...}
	will be simplified to:
		for range v {...}

This may result in changes that are incompatible with earlier versions of Go.
*/
package main

// BUG(rsc): The implementation of -r is a bit slow.
// BUG(gri): If -w fails, the restored original file may not have some of the
// original file attributes.