gh-154070: Build the curses module wide by capability, not by name

configure built the module wide (HAVE_NCURSESW) only for a backend named
ncursesw.  Probe for the wide API in the ncurses and auto backends too, so
a widec-built ncurses keeping the plain name (pkgsrc, macOS) is built wide.

Co-Authored-By: Claude Opus 4.8 <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

@@ -7219,22 +7219,27 @@ 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 Native curses ("curses") may be wide-character capable (e.g. on NetBSD)
-dnl even though it is not ncursesw.  Probe for the wide API; if present, build
-dnl the module against it like ncursesw by defining HAVE_NCURSESW.  ncursesw
-dnl already defines HAVE_NCURSESW, and ncurses must stay narrow, so only the
-dnl native backend is probed here.
-AS_VAR_IF([with_curses], [curses], [
-  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 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.  The "ncursesw"
+dnl backend already defines it, so only the other backends are probed.
+AS_CASE([$with_curses], [ncursesw|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])])