gh-154751: Keep the screen alive in curses.initscr() after newterm()

Lib/test/test_curses.py

@@ -3072,6 +3072,24 @@ def test_new_prescr(self):
         del screen
         gc_collect()
 
+    def test_initscr_after_newterm_keeps_screen_alive(self):
+        # initscr() called while a newterm() screen is current returns that
+        # screen's own standard window, so the window keeps the screen alive.
+        # It used to be a second wrapper created without a screen: using it
+        # after the screen was collected read freed memory, and both wrappers
+        # could delwin() the same window.
+        s1 = self.make_pty()
+        s2 = self.make_pty()
+        screen1 = curses.newterm('xterm', s1, s1)
+        screen2 = curses.newterm('xterm', s2, s2)
+        curses.set_term(screen1)
+        win = curses.initscr()
+        self.assertIs(win, screen1.stdscr)
+        curses.set_term(screen2)
+        del screen1
+        gc_collect()
+        win.addstr(0, 0, 'x')
+
     @cpython_only
     def test_disallow_instantiation(self):
         # The screen type cannot be instantiated directly (bpo-43916).

Modules/_cursesmodule.c

@@ -6573,7 +6573,23 @@ _curses_initscr_impl(PyObject *module)
             _curses_set_null_error(state, "wrefresh", "initscr");
             return NULL;
         }
-        PyObject *winobj = PyCursesWindow_New(state, stdscr, NULL, NULL, NULL);
+        if (state->topscreen != NULL) {
+            /* The current screen is one made by newterm(); return its own
+               standard window instead of a second wrapper over the same
+               WINDOW, which would delwin() it on its own. */
+            PyCursesScreenObject *so = (PyCursesScreenObject *)state->topscreen;
+            if (so->stdscr_win != NULL) {
+                if (curses_update_screen_encoding(so->stdscr_win) < 0) {
+                    return NULL;
+                }
+                return Py_NewRef(so->stdscr_win);
+            }
+        }
+        /* Attach the current screen, like newwin(), newpad() and getwin() do,
+           so that the window keeps its screen alive.  It is NULL for the
+           screen created by initscr(), which has no screen object. */
+        PyObject *winobj = PyCursesWindow_New(state, stdscr, NULL, NULL,
+                                              state->topscreen);
         if (winobj == NULL) {
             return NULL;
         }