commit 51d66601c45572484ed20f3a2be6f67d648b5f22
author Rob Pike <r@golang.org> Tue Mar 10 15:08:55 2015 -0700
committer Rob Pike <r@golang.org> Thu Mar 12 18:20:35 2015 +0000
tree fe6240c6fec7e160fd0f3ad6ea718c64f1b391d5
parent 6d0e87afe6beb3848bd98faed702ed7694d55059

flag: nicer usage messages

Make PrintDefaults print an easier-to-read format, and allow the user
to control it a bit by putting a hint into the usage string.

Here is the new doc comment for PrintDefaults, which does the work:

    PrintDefaults prints, to standard error unless configured otherwise, a
    usage message showing the default settings of all defined command-line
    flags. For an integer valued flag x, the default output has the form

	-x int
		usage-message-for-x (default 7)

    The usage message will appear on a separate line except for single-
    letter boolean flags. Boolean flags omit the type, since they can be
    used without an actual value, and the parenthetical default is omitted
    if the default is the zero value for the type. The type, here int, can
    be replaced by a string of the user's choosing by placing in the usage
    string for the flag a back-quoted name; the first such item in the
    message is taken to be a parameter name to show in the message and the
    back quotes are stripped from the message when displayed. For instance,
    given

	flag.String("I", "", "search `directory` for include files")

    the output will be

	-I directory
		search directory for include files.

Given

	A = flag.Bool("A", false, "for bootstrapping, allow 'any' type")
	B = flag.Bool("Alongflagname", false, "disable bounds checking")
	C = flag.Bool("C", true, "a boolean defaulting to true")
	D = flag.String("D", "", "set relative `path` for local imports")
	F = flag.Float64("F", 2.7, "a non-zero float")
	G = flag.Float64("G", 0, "a float that defaults to zero")
	N = flag.Int("N", 27, "a non-zero int")
	Z = flag.Int("Z", 0, "an int that defaults to zero")
	T = flag.Duration("deltaT", 0, "a duration")

the old output was

  -A=false: for bootstrapping, allow 'any' type
  -Alongflagname=false: disable bounds checking
  -C=true: a boolean defaulting to true
  -D="": set relative `path` for local imports
  -F=2.7: a non-zero float
  -G=0: a float that defaults to zero
  -N=27: a non-zero int
  -Z=0: an int that defaults to zero
  -deltaT=0: a duration

and the new output is

  -A	for bootstrapping, allow 'any' type
  -Alongflagname
	disable bounds checking
  -C	a boolean defaulting to true (default true)
  -D path
   	set relative path for local imports
  -F float
   	a non-zero float (default 2.7)
  -G float
   	a float that defaults to zero
  -N int
   	a non-zero int (default 27)
  -Z int
   	an int that defaults to zero
  -deltaT duration
   	a duration

Change-Id: I54ab3cd5610d551422b004d95ab78305e06a395d
Reviewed-on: https://go-review.googlesource.com/7330
Reviewed-by: Andrew Gerrand <adg@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>