Handling non-standard universal builds under superenv

[jacknagel]

For the purposes of this discussion, the "standard" universal build is the current behavior of ENV.universal_binary: passing -arch i386 -arch x86_64 to the compiler and linker.

Currently this works under both superenv and stdenv, but superenv doesn't handle things that diverge from this convention, e.g. mysql:

args << "-DCMAKE_OSX_ARCHITECTURES='i386;x86_64'" if build.universal?

this formula does not call ENV.universal_binary, so any arch flags that the build system passes to the compiler will be filtered out. The procedure for handling this has thus far been to punt and add env :std if build.universal? to the formula.

So we need to to add a switch to superenv that doesn't explicitly add universal arch flags, but doesn't filter them out, either.

One possibility would be to keep a struct representing the universal "mode" (e.g. allow_universal_flags or add_universal_flags) on the formula's BuildEnvironment object, and pass it into superenv during universal builds.

[jacknagel]

The other thing that needs to be addressed is how this should be specified in the formula DSL.

We need a way to differentiate between things where ENV.universal_binary should be called and where it should not.

[MylesBorins]

This bug is currently effecting the universal build of llvm... should we add env :std if build.universal? to the current formula?

[jacknagel]

Yeah.

[MikeMcQuaid]

In the CMake/MySQL case you could just do ENV.universal_binary and pass the CMake flag too.

[GuillaumeDIDIER]

I agree with the solution that ENV.universal_binary should simply instructs superenv to keep both -arch flags
Just keeping a list of the architecture somewhere to deduce these.
Perhaps this should be a different flag, but implied by universal binary.
I'm no ruby expert but as you said in the discussion #21534 I will try to make a pull request.

[GuillaumeDIDIER]

Here's a first piece of work (#21664).

[jacknagel]

I need to get this sorted so that we can build openssl universal. wip:

https://github.com/jacknagel/homebrew/compare/u

[jacknagel]

@Homebrew/owners - anyone want to bikeshed the name ENV.preserve_arch_flags? Open to suggestions.

[adamv]

Seems OK; does the K represent anything?

[jacknagel]

No, just picked it at random.