pythongh-109617: fix ncurses incompatibility on macOS with Xcode 15 (p…

…ython#111258)

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>
Co-authored-by: Łukasz Langa <lukasz@langa.pl>

Include/py_curses.h

@@ -23,10 +23,16 @@
 # endif
 #endif
 
-#if !defined(HAVE_CURSES_IS_PAD) && defined(WINDOW_HAS_FLAGS)
-/* The following definition is necessary for ncurses 5.7; without it,
-   some of [n]curses.h set NCURSES_OPAQUE to 1, and then Python
-   can't get at the WINDOW flags field. */
+#if defined(WINDOW_HAS_FLAGS) && defined(__APPLE__)
+/* gh-109617, gh-115383: we can rely on the default value for NCURSES_OPAQUE on
+   most platforms, but not on macOS. This is because, starting with Xcode 15,
+   Apple-provided ncurses.h comes from ncurses 6 (which defaults to opaque
+   structs) but can still be linked to older versions of ncurses dynamic
+   libraries which don't provide functions such as is_pad() to deal with opaque
+   structs. Setting NCURSES_OPAQUE to 0 is harmless in all ncurses releases to
+   this date (provided that a thread-safe implementation is not required), but
+   this might change in the future. This fix might become irrelevant once
+   support for macOS 13 or earlier is dropped. */
 #define NCURSES_OPAQUE 0
 #endif
 
@@ -39,7 +45,10 @@
 #ifdef HAVE_NCURSES_H
 /* configure was checking <curses.h>, but we will
    use <ncurses.h>, which has some or all these features. */
-#if !defined(WINDOW_HAS_FLAGS) && !(NCURSES_OPAQUE+0)
+#if !defined(WINDOW_HAS_FLAGS) && \
+    (NCURSES_VERSION_PATCH+0 < 20070303 || !(NCURSES_OPAQUE+0))
+/* the WINDOW flags field was always accessible in ncurses prior to 20070303;
+   after that, it depends on the value of NCURSES_OPAQUE. */
 #define WINDOW_HAS_FLAGS 1
 #endif
 #if !defined(HAVE_CURSES_IS_PAD) && NCURSES_VERSION_PATCH+0 >= 20090906

Misc/NEWS.d/next/Library/2023-10-24-12-39-04.gh-issue-109617.YoI8TV.rst

@@ -0,0 +1,2 @@
+:mod:`ncurses`: fixed a crash that could occur on macOS 13 or earlier when
+Python was built with Apple Xcode 15's SDK.

Modules/_cursesmodule.c

@@ -1156,8 +1156,10 @@ int py_mvwdelch(WINDOW *w, int y, int x)
 #endif
 
 #if defined(HAVE_CURSES_IS_PAD)
+// is_pad() is defined, either as a macro or as a function
 #define py_is_pad(win)      is_pad(win)
 #elif defined(WINDOW_HAS_FLAGS)
+// is_pad() is not defined, but we can inspect WINDOW structure members
 #define py_is_pad(win)      ((win) ? ((win)->_flags & _ISPAD) != 0 : FALSE)
 #endif
 
@@ -4586,17 +4588,24 @@ make_ncurses_version(PyTypeObject *type)
     if (ncurses_version == NULL) {
         return NULL;
     }
-
+    const char *str = curses_version();
+    unsigned long major = 0, minor = 0, patch = 0;
+    if (!str || sscanf(str, "%*[^0-9]%lu.%lu.%lu", &major, &minor, &patch) < 3) {
+        // Fallback to header version, which cannot be that wrong
+        major = NCURSES_VERSION_MAJOR;
+        minor = NCURSES_VERSION_MINOR;
+        patch = NCURSES_VERSION_PATCH;
+    }
 #define SetIntItem(flag) \
     PyStructSequence_SET_ITEM(ncurses_version, pos++, PyLong_FromLong(flag)); \
     if (PyErr_Occurred()) { \
         Py_CLEAR(ncurses_version); \
         return NULL; \
     }
 
-    SetIntItem(NCURSES_VERSION_MAJOR)
-    SetIntItem(NCURSES_VERSION_MINOR)
-    SetIntItem(NCURSES_VERSION_PATCH)
+    SetIntItem(major)
+    SetIntItem(minor)
+    SetIntItem(patch)
 #undef SetIntItem
 
     return ncurses_version;

configure.ac

@@ -6713,7 +6713,10 @@ AC_DEFUN([PY_CHECK_CURSES_FUNC],
     [py_var],
     [AC_COMPILE_IFELSE(
       [AC_LANG_PROGRAM(
-        [@%:@include <curses.h>], [
+        [
+        #define NCURSES_OPAQUE 0
+        #include <curses.h>
+        ], [
         #ifndef $1
         void *x=$1
         #endif