stdlib: prevent static builds on Darwin

[compnerd]

Static builds of the standard library and the SDK overlay are
unsupported post ABI stability. Disallow building of the standard
library and SDK overlay statically for Darwin platforms.

Replace this paragraph with a description of your changes and rationale. Provide links to external references/discussions if appropriate.

Resolves SR-NNNN.

[compnerd]

@swift-ci please test

[compnerd]

CC: @shahmishal @brentdax @Rostepher @gottesmm @jrose-apple

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - 7173aa3aa084c204a65bef519a561b8898602dce

[compnerd]

@swift-ci please test

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 7173aa3aa084c204a65bef519a561b8898602dce

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - f3021edf3e362e739e0a5af1ef0c2f486573538e

[beccadax]

Funny, I just filed a bug related to this: https://bugs.swift.org/browse/SR-11157

I think it would be better to not error out, though—wouldn't that make it impossible to share a preset that builds static standard libraries for non-Darwin platforms with Darwin?

[compnerd]

Yes, it does make that impossible, but, really, that is already pretty badly broken. The current model doesn't really work (CMake just is not designed that way) - e.g. -install_name being used on ELF and -soname being used for MachO?! We have a ton of hacks in place and we keep piling more on. I think that we need to just change to proper cross-compilation (nearly all the pieces are now in place). At that point, that will have different CMake sub-builds for each one. This is better long term.

[compnerd]

@swift-ci please test

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 9fb5250

[beccadax]

I think @shahmishal needs to be part of this conversation, because if we can't use the same presets on Darwin and other platforms, that's going to impact the way CI is configured.

[shahmishal]

@brentdax @compnerd Thanks for bring this to my attention, if we see build failures on CI because we are still using the flag on macOS please let me know and I will update the preset.

[beccadax]

Looking at build-presets.ini, the following apparently-Darwin presets still use this flag:

• mixin_buildbot_trunk_base
• buildbot,tools=RA-flto,stdlib=RDA
• LLDB_Swift_DebugAssert_with_devices
• LLDB_Swift_ReleaseAssert_with_devices

We should probably remove the flag from these.

[compnerd]

Beyond the update of the presets, the question is, should we even permit building the standard library/SDK overlay for Darwin in static mode?

[beccadax]

We think not permitting it is fine. There is no supported way to use the static libraries on Darwin. Mishal says that we (should) always use separate presets for Linux, so preset sharing isn't a concern.

[compnerd]

@swift-ci please test macOS platform

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 9fb5250

[compnerd]

@swift-ci please test macOS platform

[compnerd]

Sounds like all the concerns have been addressed, I'm going to go ahead and merge this. As @shahmishal said, if we run into cases where the preset is using static builds, we will update the preset and sharing is not a concern.

[shahmishal]

#26343