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

[Rui Ueyama via llvm-dev]

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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