[3.9] bpo-42681: Fix test_curses failures related to color pairs (GH-24089)

On ncurses 6.1 pair numbers are limited by SHORT_MAX-1, even
with extended color support.

Improve error reporting and tests for color functions..
(cherry picked from commit 59f9b4e450)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

Lib/test/test_curses.py

@@ -323,11 +323,20 @@ class TestCurses(unittest.TestCase):
     def bad_pairs(self):
         return (-2**31 - 1, 2**31, -2**63 - 1, 2**63, 2**64)
 
+    def test_start_color(self):
+        if not curses.has_colors():
+            self.skipTest('requires colors support')
+        curses.start_color()
+        if verbose:
+            print(f'COLORS = {curses.COLORS}', file=sys.stderr)
+            print(f'COLOR_PAIRS = {curses.COLOR_PAIRS}', file=sys.stderr)
+
     @requires_colors
     def test_color_content(self):
         self.assertEqual(curses.color_content(curses.COLOR_BLACK), (0, 0, 0))
         curses.color_content(0)
-        curses.color_content(min(curses.COLORS - 1, SHORT_MAX))
+        maxcolor = min(curses.COLORS - 1, SHORT_MAX)
+        curses.color_content(maxcolor)
 
         for color in self.bad_colors():
             self.assertRaises(OverflowError, curses.color_content, color)
@@ -368,13 +377,18 @@ class TestCurses(unittest.TestCase):
             self.assertRaises(curses.error, curses.init_color, 0, 0, comp, 0)
             self.assertRaises(curses.error, curses.init_color, 0, 0, 0, comp)
 
+    def get_pair_limit(self):
+        return min(curses.COLOR_PAIRS, SHORT_MAX)
+
     @requires_colors
     def test_pair_content(self):
         if not hasattr(curses, 'use_default_colors'):
             self.assertEqual(curses.pair_content(0),
                              (curses.COLOR_WHITE, curses.COLOR_BLACK))
         curses.pair_content(0)
-        curses.pair_content(min(curses.COLOR_PAIRS - 1, SHORT_MAX))
+        maxpair = self.get_pair_limit() - 1
+        if maxpair > 0:
+            curses.pair_content(maxpair)
 
         for pair in self.bad_pairs():
             self.assertRaises(OverflowError, curses.pair_content, pair)
@@ -389,11 +403,14 @@ class TestCurses(unittest.TestCase):
         curses.init_pair(1, 0, 0)
         self.assertEqual(curses.pair_content(1), (0, 0))
         maxcolor = min(curses.COLORS - 1, SHORT_MAX)
-        curses.init_pair(1, maxcolor, maxcolor)
+        curses.init_pair(1, maxcolor, 0)
-        self.assertEqual(curses.pair_content(1), (maxcolor, maxcolor))
+        self.assertEqual(curses.pair_content(1), (maxcolor, 0))
-        maxpair = min(curses.COLOR_PAIRS - 1, SHORT_MAX)
+        curses.init_pair(1, 0, maxcolor)
-        curses.init_pair(maxpair, 2, 3)
+        self.assertEqual(curses.pair_content(1), (0, maxcolor))
-        self.assertEqual(curses.pair_content(maxpair), (2, 3))
+        maxpair = self.get_pair_limit() - 1
+        if maxpair > 1:
+            curses.init_pair(maxpair, 0, 0)
+            self.assertEqual(curses.pair_content(maxpair), (0, 0))
 
         for pair in self.bad_pairs():
             self.assertRaises(OverflowError, curses.init_pair, pair, 0, 0)
@@ -591,6 +608,8 @@ class MiscTests(unittest.TestCase):
     @requires_curses_func('ncurses_version')
     def test_ncurses_version(self):
         v = curses.ncurses_version
+        if verbose:
+            print(f'ncurses_version = {curses.ncurses_version}', flush=True)
         self.assertIsInstance(v[:], tuple)
         self.assertEqual(len(v), 3)
         self.assertIsInstance(v[0], int)

Modules/_cursesmodule.c

@@ -2592,13 +2592,18 @@ _curses_color_content_impl(PyObject *module, short color_number)
     PyCursesInitialised;
     PyCursesInitialisedColor;
 
-    if (color_content(color_number, &r, &g, &b) != ERR)
+    if (color_content(color_number, &r, &g, &b) == ERR) {
-        return Py_BuildValue("(iii)", r, g, b);
+        if (color_number >= COLORS) {
-    else {
             PyErr_SetString(PyCursesError,
                             "Argument 1 was out of range. Check value of COLORS.");
+        }
+        else {
+            PyErr_SetString(PyCursesError, "color_content() returned ERR");
+        }
         return NULL;
     }
+
+    return Py_BuildValue("(iii)", r, g, b);
 }
 
 /*[clinic input]
@@ -3702,8 +3707,13 @@ _curses_pair_content_impl(PyObject *module, short pair_number)
     PyCursesInitialisedColor;
 
     if (pair_content(pair_number, &f, &b) == ERR) {
+        if (pair_number >= COLOR_PAIRS) {
             PyErr_SetString(PyCursesError,
                             "Argument 1 was out of range. (0..COLOR_PAIRS-1)");
+        }
+        else {
+            PyErr_SetString(PyCursesError, "pair_content() returned ERR");
+        }
         return NULL;
     }