[llvm-dev] Accept --long-option but not -long-option for llvm binary utilities

[Don Hinton via llvm-dev]

It's actually a bit weirder than you might think.  The CommandLine parser
will happily eat as many dashes as you care to write, e.g., `----sections`
is the same as `-sections`.


On Tue, Apr 16, 2019 at 2:11 AM James Henderson via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> As I think I said elsewhere, I find it weird that LLVM tools accept long
> arguments with a single dash, and I'd be happy for the binary utilities at
> least to move away from this approach, if it improves compatibility/reduces
> gotchas etc. One of the points from the BoF on the LLVM binutils at the
> recent Euro LLVM developers' meeting was that if we are going to break
> compatibility with previous versions of LLVM, we're better off doing it
> now, rather than leaving it a long time. The longer it gets left, the more
> users, and therefore the more likely somebody has come to rely on it in a
> non-trivial-to-fix way.
>
> If we are particularly concerned with llvm-readobj, we could (if it is
> practical) try handling it differently to llvm-readelf. An approach as
> suggested by Michael Spencer at the BoF could be to migrate away from using
> cl::opt and follow the same route as llvm-objcopy. That would allow us to
> have different option sets for the two versions of that tool, if we wanted.
>
> On Tue, 16 Apr 2019 at 08:44, Jordan Rupprecht <rupprecht at google.com>
> wrote:
>
>> For binutil compatibility, and in general for any new tools, this sounds
>> reasonable to me. But I'd worry that things like llvm-readobj have existed
>> for a long time and people are used to flags like "-sections", and it may
>> be complicated to change that now. (I guess this RFC is a check to see if
>> this is true for anyone on the mailing list).
>>
>> What happens if you make this change and someone does use "-sections" --
>> will the command line parser suggest "--sections", or will it just fail
>> because one of -s, -e, -c, etc. is not a valid option?
>>
>> On Tue, Apr 16, 2019 at 9:00 AM Rui Ueyama via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>>> That change makes sense to me. I'd like to note that the policy should
>>> be set per-command basis, as some commands are required to accept both `--`
>>> and `-` for long option names. lld is such command.
>>>
>>> On Tue, Apr 16, 2019 at 3:41 PM Fāng-ruì Sòng via llvm-dev <
>>> llvm-dev at lists.llvm.org> wrote:
>>>
>>>> Many llvm utilities use cl::ParseCommandLineOptions()
>>>> (include/Support/CommandLine.h) to parse command line options. The cl
>>>> library accepts both -long-option and --long-option forms, with the single
>>>> dash form (-long-option) being more popular.
>>>>
>>>> We also have many binary utilities (llvm-objcopy llvm-objdump
>>>> llvm-readobj llvm-size ...) whose names reflect what they imitate. For
>>>> compatibility with GNU binutils (and some Unix utilities transitively),
>>>> these utilities accept many short options. People who use llvm utilities as
>>>> replacement of GNU binutils may use the grouped option syntax (POSIX
>>>> Utility Conventions), e.g. -Sx => -S -x, -Wd => -W -d, -sj.text => -s
>>>> -j.text
>>>>
>>>> The problem is, grouped short options don't play well with
>>>> -long-option. Sometimes there can be ambiguity. The issue is more prominent
>>>> if the short option accepts an argument.
>>>>
>>>> An approach to prevent the ambiguity is to just disallow -long-option.
>>>> In D60439, I plan to make llvm-objcopy accept --long-option but not
>>>> -long-option.
>>>> It will make its command line option parsing behave more like GNU
>>>> objcopy and less like a regular llvm utility. What do people think of the
>>>> divergence?
>>>>
>>>> Further, can we make similar changes to other llvm binary utilities
>>>> (their names give people the expectation), especially those with many short
>>>> options such as llvm-objdump and llvm-readobj? llvm-readobj behaves like
>>>> GNU readelf if you name it "llvm-readelf". (I don't suggest disallowing
>>>> -long-option for utilities other than binutils)
>>>>
>>>> (Note, llvm-objcopy is a new member of the family and it uses tablegen
>>>> based include/llvm/Option/Opton.h, instead of cl:: as other utilities do.)
>>>>
>>>>
>>>>
>>>> --
>>>> 宋方睿
>>>> _______________________________________________
>>>> LLVM Developers mailing list
>>>> llvm-dev at lists.llvm.org
>>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org
>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
>> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20190416/98ff0763/attachment.html>