gh-109617: fix ncurses incompatibility on macOS with Xcode 15

[sorcio]

macOS 14 ships with a new version of ncurses¹. But their new SDK tries to support both the old and the new version at build time in a way that CPython's configure script could not correctly detect.

1. Default to using NCURSES_OPAQUE = 0 which, when using ncurses, avoids the use of some exported functions, such as is_pad². The macro versions are used instead.
2. Since the same build can dynamically link against significantly different ncurses implementations, query the version information at runtime instead of hardcoding it.

Question: do we want to limit the change to macOS, or possibly make it conditional to MACOSX_DEPLOYMENT_TARGET < 14.0?

• Issue: Refresh Screen Provided By curses.wrapper Causes Seg Fault (macOS, xcode 15 Apple supplied ncurses 6.0 breakage) #109617

Footnotes

1. for a long time, macOS has shipped a libncurses version based on ncurses 5.7.20081102. Since macOS 14.0, the version seems to be 6.0.20150808 plus some patches. ↩

2. see https://invisible-island.net/ncurses/man/curs_opaque.3x.html. Opaque mode would be necessary to use the alternative libncursest (ncurses thread-safer ABI) but Python does not use it. ↩

[vstinner]

Can you explain the version check in the comment?

[serhiy-storchaka]

The current code do not use pechochar(), pnoutrefresh(), prefresh() and subpad() if neither HAVE_CURSES_IS_PAD nor WINDOW_HAS_FLAGS are defined. It allows to build with the curses implementation that does not support pads and does not have these function.

This PR makes the above functions required.

[sorcio]

The current code do not use pechochar(), pnoutrefresh(), prefresh() and subpad() if neither HAVE_CURSES_IS_PAD nor WINDOW_HAS_FLAGS are defined. It allows to build with the curses implementation that does not support pads and does not have these function.

This PR makes the above functions required.

Thanks, I missed that. I will revert to the macro version. Do you have a suggestion on how to test for those implementations?

[hugovk]

Updated from main to trigger the CI and see if this fixes the new #115383.

[hugovk]

We got lucky with GitHub Actions runner image allocation.

The free-threaded build ran on the older 20240114.1 with Xcode 14 (which has recently started failing):

• https://github.com/python/cpython/actions/runs/7883963392/job/21511964656?pr=111258

And the regular build ran on the newer 20240204.1 with Xcode 15:

• https://github.com/python/cpython/actions/runs/7883963392/job/21511964137?pr=111258

And both passed 👍

[sorcio]

I updated the patch according to feedback:

• reverted to the py_is_pad definition as a macro, so that it can build with curses implementation that don't have pechochar(), pnoutrefresh(), prefresh() or subpad()
• added some comments to clarify context

I left in the code that parses ncurses version. It addresses a problem that only arises once this fix is available (that is, static version could report 6 but the interpreter could be loading 5 if running on older macOS). I can remove if this feels too controversial, or split to a new issue.