bpo-25720: Fix the method for checking pad state of curses WINDOW (GH-4164) (#4212)

Modify the code to use ncurses is_pad() instead of checking WINDOW
_flags field.  If your platform does not provide the is_pad(), the
existing way that checks the field will be enabled.

Note: This change does not drop support for platforms where do not
have both WINDOW _flags field and is_pad().
(cherry picked from commit 8bc7d63560024681dce9f40445f2877b2987e92c)

1 files changed, 38 insertions, 1 deletions

diff --git a/configure b/configure
index 37f68ed..7ca386f 100755
--- a/configure
+++ b/configure
@@ -15897,6 +15897,10 @@ $as_echo "#define MVWDELCH_IS_EXPRESSION 1" >>confdefs.h
 
 fi
 
+# Issue #25720: ncurses has introduced the NCURSES_OPAQUE symbol making opaque
+# structs since version 5.7.  If the macro is defined as zero before including
+# [n]curses.h, ncurses will expose fields of the structs regardless of the
+# configuration.
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether WINDOW has _flags" >&5
 $as_echo_n "checking whether WINDOW has _flags... " >&6; }
 if ${ac_cv_window_has_flags+:} false; then :
@@ -15904,7 +15908,10 @@ if ${ac_cv_window_has_flags+:} false; then :
 else
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
-#include <curses.h>
+
+  #define NCURSES_OPAQUE 0
+  #include <curses.h>
+
 int
 main ()
 {
@@ -15935,6 +15942,36 @@ $as_echo "#define WINDOW_HAS_FLAGS 1" >>confdefs.h
 
 fi
 
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for is_pad" >&5
+$as_echo_n "checking for is_pad... " >&6; }
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+#include <curses.h>
+int
+main ()
+{
+
+#ifndef is_pad
+void *x=is_pad
+#endif
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+
+$as_echo "#define HAVE_CURSES_IS_PAD 1" >>confdefs.h
+
+   { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+$as_echo "yes" >&6; }
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for is_term_resized" >&5
 $as_echo_n "checking for is_term_resized... " >&6; }
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext