code review 156390043: flag: disallow setting flags multiple times

flag: disallow setting flags multiple times
This is a day 1 error in the flag package: It did not check
that a flag was set at most once on the command line.
Because user-defined flags may have more general
properties, the check applies only to the standard flag
types in this package: bool, string, etc.

Fixes issue 8960.

[r, 2014-10-19 15:57:19]

Hello golang-codereviews@googlegroups.com,

I'd like you to review this change to
https://code.google.com/p/go/

[bradfitz, 2014-10-19 16:08:46]

LGTM

https://codereview.appspot.com/156390043/diff/1/src/flag/flag.go
File src/flag/flag.go (right):

https://codereview.appspot.com/156390043/diff/1/src/flag/flag.go#newcode733
src/flag/flag.go:733: case *intValue:
don't like the comma-separated cases? seems a bit lighter on the page, at the
cost of one line looking different. either way.

[r, 2014-10-19 17:17:56]

https://codereview.appspot.com/156390043/diff/1/src/flag/flag.go
File src/flag/flag.go (right):

https://codereview.appspot.com/156390043/diff/1/src/flag/flag.go#newcode733
src/flag/flag.go:733: case *intValue:
On 2014/10/19 16:08:46, bradfitz wrote:
> don't like the comma-separated cases? seems a bit lighter on the page, at the
> cost of one line looking different. either way.

because they don't work the way I want them to in type switches, my brain
forgets that they work at all.
fixed.

[r, 2014-10-19 17:33:25]

*** Submitted as https://code.google.com/p/go/source/detail?r=973cf6fc03b8 ***

flag: disallow setting flags multiple times
This is a day 1 error in the flag package: It did not check
that a flag was set at most once on the command line.
Because user-defined flags may have more general
properties, the check applies only to the standard flag
types in this package: bool, string, etc.

Fixes issue 8960.

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://codereview.appspot.com/156390043

[gobot, 2014-10-19 17:40:43]

This CL appears to have broken the plan9-amd64-aram builder.
See http://build.golang.org/log/488be71979aeed73dd255bd67169d794fbb7669b

[rsc, 2014-10-20 19:09:20]

In typical Unix command line environments if you specify a flag multiple times,
the last one wins, which is exactly what was going on here. This was true even
on Plan 9, but also in the BSD and GNU flag parsers. So this was working as I
expected, and as I believe many others would expect.

If we'd decided to do something different on day 1 I would probably have gone
along with trying it, but I don't think we can break that behavior today.