Restore ncurses widechar support on macOS

[sorcio]

Bug report

Bug description:

Python 3.12 dropped ncurses wide char support on macOS, so for example curses.get_wch() is not available anymore.

I believe this was an unintended consequence of #94452, because the change is not documented anywhere. After that PR, HAVE_NCURSESW is never defined on Darwin. It looks like this bit of logic was not ported from setup.py to configure.ac:

cpython/setup.py

Lines 1121 to 1124 in ec5e253

	elif MACOS and curses_library == 'ncurses':
	# Building with the system-suppied combined libncurses/libpanel
	curses_defines.append(('HAVE_NCURSESW', '1'))
	curses_defines.append(('_XOPEN_SOURCE_EXTENDED', '1'))

In fact, wide char support is always available when using Apple-provided ncurses, and it used to work correctly in the 3.11 builds that I tested.

@tiran can you confirm that this was unintended?

cc @sobolevn who interpreted this as an intended change in python/typeshed#10808.

CPython versions tested on:

3.12, 3.13

Operating systems tested on:

macOS

Linked PRs

• gh-111460: restore ncurses widechar support on macOS #111878
• [3.12] gh-111460: Restore ncurses widechar support on macOS (GH-111878) #112034

[ned-deily]

@erlend-aasland

[erlend-aasland]

Yes, this is probably an unintended side effect. I can look into it tomorrow.

(cc. @corona10, if you are interested)

[corona10]

Yeah I will take a look too

[sorcio]

Would it be interesting to encode some platform expectations in tests?

This regression went under the radar because test_unget_wch is skipped with @requires_curses_func('unget_wch'), among other reasons. Skipping makes sense in general. But in some build configurations (including macOS CI, macOS buildbots, and the official macOS installer) we know that we are building with ncurses, and unget_wch should exist.

Since this functionality is documented to be generally available, should a test assert that it actually is?

[sorcio]

Maybe it was a one-character fix after all: #111878

(Note: if you are testing curses on macOS <14, you might need #111258 or a similar fix)

Should some test be added?

[erlend-aasland]

Can this be closed?

[sorcio]

@erlend-aasland if there is no need to test this, we're done here.

[erlend-aasland]

@erlend-aasland if there is no need to test this, we're done here.

There's always a need for accompanying tests.

[sorcio]

I need help with this then. What is a test supposed to test? We could say that wide char support should always be there on Darwin, but it could fail on builds that bring their own curses (or not).

[ronaldoussoren]

@erlend-aasland : What kind of tests do you want to see here? AFAIK we generally don't test if expected platform features are present, other than some tests I've added when working on the Universal 2 port to ensure that weak linking works as expected.

[erlend-aasland]

I did not have anything in particular in mind. If there is no particular need, let's just close this.