Cross-platform all bottles: shebangs

[Bo98]

Provide a detailed description of the proposed feature

One key difference between macOS and Linux is how we use system Perl (and other scripting languages) on macOS but use brewed Perl on Linux.

This leads to different shebangs in some cases, with macOS pointing to /usr/bin/perl and Linux pointing to HOMEBREW_PREFIX/opt/perl/bin/perl.

In order to achieve cross-platform bottles, we could use keg-relocation logic to replace the shebangs with @@HOMEBREW_PERL@@ which can be replaced with the correct shebang at pour time.

What is the motivation for the feature?

Achieving cross-platform all bottles where possible.

How will the feature be relevant to at least 90% of Homebrew users?

Formulae which have all bottles can be installed on any platform without having to build from source - rather than be limited to just what we run CI on.

What alternatives to the feature have been considered?

An alternative is to stop using system Perl and use brewed Perl universally.

[iMichka]

An alternative is to stop using system Perl and use brewed Perl universally.

If I remember well, Apple plans to drop all scripting languages (like ruby, Python, ...). Don't know what is the fate of system perl. On the other hand they started providing Python 3 through the CLT, so their way of doing things is not super consistent.

[Bo98]

Yeah they do plan to do something, albeit it's not very clear exactly what. They say "future versions of macOS won’t include scripting language runtimes by default, and might require you to install additional packages."

"Additional packages" might refer to the CLT, but this would indeed still be a concern for us since we do support the no-devtools case.

[MikeMcQuaid]

In order to achieve cross-platform bottles, we could use keg-relocation logic to replace the shebangs with @@HOMEBREW_PERL@@ which can be replaced with the correct shebang at pour time.

👍🏻

How/why does this happen, is it just uses_from_macos related? If so, perhaps something more generic could be done to use these uses_from_macos lines to replace system dependencies with Homebrew ones in these cases?

If I remember well, Apple plans to drop all scripting languages (like ruby, Python, ...).

They've announced it but I wouldn't bet on it happening for a good while. While we still have system libraries/languages: let's use them. That's kinda why Homebrew originally came into creation.

[Bo98]

How/why does this happen, is it just uses_from_macos related? If so, perhaps something more generic could be done to use these uses_from_macos lines to replace system dependencies with Homebrew ones in these cases?

Pretty much yes.

ExtUtils::MakeMaker will detect itself what perl executable is being run and use that as the shebang, and in other cases our own rewrite_shebang also does something similar to use /usr/bin/perl if we have uses_from_macos and HOMEBREW_PREFIX/opt/perl/bin/perl otherwise.

[MikeMcQuaid]

Ah, this is pretty much only a thing because of rewrite_shebang, right? I think in that case it'd be reasonable to only handle those cases (or store enough state so that we know we need to fix up those cases when we do rewrite shebangs).

[Bo98]

this is pretty much only a thing because of rewrite_shebang, right?

Perl's ExtUtils::MakeMaker also does it.

[MikeMcQuaid]

Gotcha. Makes sense to me to do it for Python/Perl, then 👍🏻. Thanks @Bo98!

[github-actions]

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[Bo98]

This was addressed in #11286.