[3.15] gh-154070: Build the curses module wide by capability, not by name (GH-154071)

configure built the module wide (HAVE_NCURSESW) only for a library found
under the name ncursesw.  Probe for the wide API too, so a widec-built
ncurses keeping the plain name (pkgsrc, macOS) is built wide.

3.15 has no --with-curses, so the probe is guarded on curses being found
rather than on the selected backend.
(cherry picked from commit 2db8ca7)

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: serhiy-storchaka

Misc/NEWS.d/next/Build/2026-07-19-12-16-31.gh-issue-154070.f5da07.rst

@@ -0,0 +1,4 @@
+Build the :mod:`curses` module against a wide-character capable ncurses
+even when it is not named ``ncursesw`` -- for example the pkgsrc ncurses on
+NetBSD and illumos, or the system ncurses on macOS.  Such a library
+previously produced a narrow build.

configure

@@ -7194,6 +7194,31 @@ AS_VAR_IF([ac_sys_system], [Darwin], [
 dnl pyconfig.h defines _XOPEN_SOURCE=700
 PANEL_CFLAGS=$(echo $PANEL_CFLAGS | sed 's/-D_XOPEN_SOURCE=600//g')
 
+dnl A curses that is not named "ncursesw" can still be wide-character capable:
+dnl the system curses of NetBSD, or an ncurses built with --enable-widec that
+dnl keeps the plain name (pkgsrc, macOS).  Probe for the wide API and, if
+dnl present, build the module wide by defining HAVE_NCURSESW.
+AS_VAR_IF([have_curses], [no], [], [
+  WITH_SAVE_ENV([
+    dnl Use the adjusted CURSES_CFLAGS (e.g. macOS's -D_XOPEN_SOURCE_EXTENDED)
+    dnl so the wide-character declarations are visible to the probe.
+    AS_VAR_APPEND([CPPFLAGS], [" $CURSES_CFLAGS"])
+    AC_CACHE_CHECK([whether curses supports wide characters],
+      [ac_cv_curses_wide],
+      [AC_LINK_IFELSE(
+        [AC_LANG_PROGRAM([_CURSES_INCLUDES], [[
+          cchar_t wcval;
+          setcchar(&wcval, L"x", A_NORMAL, 0, NULL);
+          add_wch(&wcval);
+        ]])],
+        [ac_cv_curses_wide=yes],
+        [ac_cv_curses_wide=no])])
+  ])
+  dnl HAVE_NCURSESW marks the wide (cchar_t) curses API; its template comes
+  dnl from the ncursesw pkg-config check above, so no description here.
+  AS_VAR_IF([ac_cv_curses_wide], [yes], [AC_DEFINE([HAVE_NCURSESW], [1])])
+])
+
 # On Solaris, term.h requires curses.h
 AC_CHECK_HEADERS([term.h], [], [], _CURSES_INCLUDES)