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

[James Henderson via llvm-dev]

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
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>>> llvm-dev at lists.llvm.org
>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
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