pythongh-127349: Add check for correct resizing in REPL (python#127387)

(cherry picked from commit 510fefd)

Lib/_pyrepl/reader.py

@@ -587,10 +587,11 @@ def setpos_from_xy(self, x: int, y: int) -> None:
     def pos2xy(self) -> tuple[int, int]:
         """Return the x, y coordinates of position 'pos'."""
         # this *is* incomprehensible, yes.
-        y = 0
+        p, y = 0, 0
+        l2: list[int] = []
         pos = self.pos
         assert 0 <= pos <= len(self.buffer)
-        if pos == len(self.buffer):
+        if pos == len(self.buffer) and len(self.screeninfo) > 0:
             y = len(self.screeninfo) - 1
             p, l2 = self.screeninfo[y]
             return p + sum(l2) + l2.count(0), y

Lib/test/test_pyrepl/test_reader.py

@@ -2,10 +2,9 @@
 import functools
 import rlcompleter
 from unittest import TestCase
-from unittest.mock import MagicMock, patch
+from unittest.mock import MagicMock
 
-from .support import handle_all_events, handle_events_narrow_console, code_to_events, prepare_reader
-from test.support import import_helper
+from .support import handle_all_events, handle_events_narrow_console, code_to_events, prepare_reader, prepare_console
 from _pyrepl.console import Event
 from _pyrepl.reader import Reader
 
@@ -313,3 +312,10 @@ def test_key_press_on_tab_press_once(self):
         reader, _ = handle_all_events(events, prepare_reader=completing_reader)
 
         self.assert_screen_equals(reader, f"{code}a")
+
+    def test_pos2xy_with_no_columns(self):
+        console = prepare_console([])
+        reader = prepare_reader(console)
+        # Simulate a resize to 0 columns
+        reader.screeninfo = []
+        self.assertEqual(reader.pos2xy(), (0, 0))

Misc/NEWS.d/next/Core_and_Builtins/2024-11-30-16-13-31.gh-issue-127349.ssYd6n.rst

@@ -0,0 +1,2 @@
+Fixed the error when resizing terminal in Python REPL. Patch by Semyon
+Moroz.