gh-155976: Refresh COLORS and COLOR_PAIRS in curses set_term

Lib/test/test_curses.py

@@ -14,6 +14,7 @@
                           check_disallow_instantiation, MISSING_C_DOCSTRINGS,
                           gc_collect, SHORT_TIMEOUT)
 from test.support.import_helper import import_module
+from test.support import os_helper
 
 # Optionally test curses module.  This currently requires that the
 # 'curses' resource be given on the regrtest command line using the -u
@@ -3324,6 +3325,45 @@ def test_set_term(self):
         self.assertIs(curses.set_term(a), b)  # returns the previous one
         self.assertIs(curses.set_term(b), a)
 
+    def test_set_term_refreshes_lines_cols_colors(self):
+        s1 = self.make_pty()
+        s2 = self.make_pty()
+
+        with os_helper.EnvironmentVarGuard() as env:
+            env['LINES'] = '25'
+            env['COLUMNS'] = '80'
+            try:
+                a = curses.newterm('xterm', s1, s1)
+            except curses.error:
+                self.skipTest('no xterm terminfo entry')
+            try:
+                curses.start_color()
+            except curses.error:
+                pass
+
+            env['LINES'] = '30'
+            env['COLUMNS'] = '100'
+            try:
+                b = curses.newterm('xterm-256color', s2, s2)
+            except curses.error:
+                self.skipTest('no xterm-256color terminfo entry')
+            try:
+                curses.start_color()
+            except curses.error:
+                pass
+
+        curses.set_term(a)
+        self.assertEqual((curses.LINES, curses.COLS), a.stdscr.getmaxyx())
+        self.assertNotEqual((curses.LINES, curses.COLS), b.stdscr.getmaxyx())
+        if hasattr(curses, 'COLORS'):
+            self.assertEqual(curses.COLORS, 8)
+
+        self.assertEqual(curses.set_term(b), a)
+        self.assertEqual((curses.LINES, curses.COLS), b.stdscr.getmaxyx())
+        self.assertNotEqual((curses.LINES, curses.COLS), a.stdscr.getmaxyx())
+        if hasattr(curses, 'COLORS'):
+            self.assertEqual(curses.COLORS, 256)
+
     def test_window_keeps_screen_alive(self):
         # The standard window keeps its screen alive; dropping every other
         # reference and collecting must not invalidate the window.

Modules/_cursesmodule.c

@@ -7890,7 +7890,11 @@ update_lines_cols(PyObject *private_module)
         goto error;
     }
 
-    o = PyLong_FromLong(LINES);
+    int lines = LINES;
+    if (stdscr != NULL) {
+        lines = getmaxy(stdscr);
+    }
+    o = PyLong_FromLong(lines);
     if (o == NULL) {
         goto error;
     }
@@ -7902,7 +7906,11 @@ update_lines_cols(PyObject *private_module)
     }
     Py_DECREF(o);
 
-    o = PyLong_FromLong(COLS);
+    int cols = COLS;
+    if (stdscr != NULL) {
+        cols = getmaxx(stdscr);
+    }
+    o = PyLong_FromLong(cols);
     if (o == NULL) {
         goto error;
     }
@@ -7913,6 +7921,32 @@ update_lines_cols(PyObject *private_module)
         goto error;
     }
     Py_DECREF(o);
+
+    if (curses_start_color_called) {
+        o = PyLong_FromUnsignedLongLong((unsigned long long)COLORS);
+        if (o == NULL) {
+            goto error;
+        }
+        if (PyDict_SetItemString(exposed_module_dict, "COLORS", o) < 0) {
+            goto error;
+        }
+        if (PyDict_SetItemString(private_module_dict, "COLORS", o) < 0) {
+            goto error;
+        }
+        Py_DECREF(o);
+
+        o = PyLong_FromUnsignedLongLong((unsigned long long)COLOR_PAIRS);
+        if (o == NULL) {
+            goto error;
+        }
+        if (PyDict_SetItemString(exposed_module_dict, "COLOR_PAIRS", o) < 0) {
+            goto error;
+        }
+        if (PyDict_SetItemString(private_module_dict, "COLOR_PAIRS", o) < 0) {
+            goto error;
+        }
+        Py_DECREF(o);
+    }
     Py_DECREF(exposed_module);
     return 1;