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

Tue Apr 16 18:50:13 PDT 2019

It does this in a few places:

      // Eat leading dashes.
      while (!ArgName.empty() && ArgName[0] == '-')
        ArgName = ArgName.substr(1);

On Tue, Apr 16, 2019 at 6:47 PM Rui Ueyama <ruiu at google.com> wrote:

> On Wed, Apr 17, 2019 at 10:42 AM Don Hinton via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> 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`.
>>
>
> That seems true, and I'm a bit surprised. Accepting three or more dashes
> is definitely a bug.
>
> 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
>>>>>>
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>>>>>
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>
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