[cfe-dev] python vs python3 shebang

[Valeriy Savchenko via cfe-dev]

> Any idea where this hack lives? Would be nice to check if it's updated.
It’s not a hack in the LLVM codebase (that would be easier). What I remember from previous discussions about Python, is that it finds #!/usr/bin/env python and uses installed Python2 interpreter or something, but doesn’t have the same trick for python3 or smth.
But again, I can be very wrong here.

-Valeriy

> On 22 Apr 2021, at 13:16, Sam McCall <sammccall at google.com> wrote:
> 
> This is coming up now in part because debian testing has removed /usr/bin/python, so #!/usr/bin/env python no longer works on such systems.
> 
> Relevant is https://www.python.org/dev/peps/pep-0394/ <https://www.python.org/dev/peps/pep-0394/>, which I think basically says if we want to maintain scripts that work both on py2-only systems and py3-only systems there's no real answer other than adding an installer that rewrites the shebang lines :-(
> 
> Agree that for tools used by LLVM devs #!/usr/bin/env python3 seems like a good change.
> For user-facing tools it seems we have 3 "easy" options for the checked-in scripts:
> A) use python2 and break on some new systems
> B) use python3 and break on some old systems
> C) use python and break on systems that don't provide the alias
> None of these seem nice.
> 
> > As far as I remember, it’s trickier on Windows where there is a special hack for shebang to python specifically.
> 
> Any idea where this hack lives? Would be nice to check if it's updated.
> 
> On Thu, Apr 22, 2021 at 11:30 AM Haojian Wu <hokein at google.com <mailto:hokein at google.com>> wrote:
> Hello folks,
> 
> We have a mixture of python(2) vs python3 shebang usage in llvm codebase.
> 
> As python2 upstream support has ended, what's the LLVM policy here? Shall we change the shebang to python3 for all scripts? 
> 
> - For llvm-developer-only python scripts (e.g. clang-tidy/add_new_check.py), it is safe to do this change, as LLVM development <https://llvm.org/docs/GettingStarted.html#software> requires python >= 3.6 
> - For python scripts being interacted with people's workflow (e.g. clang-format-diff.py), it seems unclear to me, changing the shebang would break people's workflow on python2 machines.
> 
> I have some patches (https://reviews.llvm.org/D101038 <https://reviews.llvm.org/D101038>, https://reviews.llvm.org/D101037 <https://reviews.llvm.org/D101037>). What do people think?
> 
> 
> Thanks,
> Haojian

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