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// 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.
gofmt [flags] [path ...]
The flags are:
Do not print reformatted sources to standard output.
If a file's formatting is different than gofmt's, print diffs
to standard output.
Print all (including spurious) errors.
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.
Try to simplify code (after applying the rewrite rule, if any).
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.
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:
will be simplified to:
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.
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