[cfe-dev] python vs python3 shebang

[Sam McCall via cfe-dev]

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/, 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> 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/D101037). What do people think?
>
>
> Thanks,
> Haojian
>
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