PyREPL crashes when there aren't enough columns

[trag1c]

Bug report

Bug description:

To reproduce

_{(order doesn't matter)}

• Open the new REPL
• Resize the terminal emulator window to be less than 5 cells wide

Traceback

Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "/Users/trag1c/.pyenv/versions/3.13.0/lib/python3.13/_pyrepl/__main__.py", line 6, in <module>
    __pyrepl_interactive_console()
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^
  File "/Users/trag1c/.pyenv/versions/3.13.0/lib/python3.13/_pyrepl/main.py", line 59, in interactive_console
    run_multiline_interactive_console(console)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^
  File "/Users/trag1c/.pyenv/versions/3.13.0/lib/python3.13/_pyrepl/simple_interact.py", line 151, in run_multiline_interactive_console
    statement = multiline_input(more_lines, ps1, ps2)
  File "/Users/trag1c/.pyenv/versions/3.13.0/lib/python3.13/_pyrepl/readline.py", line 389, in multiline_input
    return reader.readline()
           ~~~~~~~~~~~~~~~^^
  File "/Users/trag1c/.pyenv/versions/3.13.0/lib/python3.13/_pyrepl/reader.py", line 801, in readline
    self.handle1()
    ~~~~~~~~~~~~^^
  File "/Users/trag1c/.pyenv/versions/3.13.0/lib/python3.13/_pyrepl/reader.py", line 770, in handle1
    self.refresh()
    ~~~~~~~~~~~~^^
  File "/Users/trag1c/.pyenv/versions/3.13.0/lib/python3.13/_pyrepl/reader.py", line 691, in refresh
    self.screen = self.calc_screen()
                  ~~~~~~~~~~~~~~~~^^
  File "/Users/trag1c/.pyenv/versions/3.13.0/lib/python3.13/_pyrepl/completing_reader.py", line 261, in calc_screen
    screen = super().calc_screen()
  File "/Users/trag1c/.pyenv/versions/3.13.0/lib/python3.13/_pyrepl/reader.py", line 413, in calc_screen
    self.cxy = self.pos2xy()
               ~~~~~~~~~~~^^
  File "/Users/trag1c/.pyenv/versions/3.13.0/lib/python3.13/_pyrepl/reader.py", line 595, in pos2xy
    p, l2 = self.screeninfo[y]
            ~~~~~~~~~~~~~~~^^^
IndexError: list index out of range

The relevant fragment of code

cpython/Lib/_pyrepl/reader.py

Lines 587 to 596 in f4e5643

	def pos2xy(self) -> tuple[int, int]:
	"""Return the x, y coordinates of position 'pos'."""
	# this *is* incomprehensible, yes.
	y = 0
	pos = self.pos
	assert 0 <= pos <= len(self.buffer)
	if pos == len(self.buffer):
	y = len(self.screeninfo) - 1
	p, l2 = self.screeninfo[y]
	return p + sum(l2) + l2.count(0), y

An additional demo

Screen.Recording.2024-11-27.at.11.47.29.PM.mov

CPython versions tested on:

3.13, 3.14

Operating systems tested on:

Linux, macOS

Linked PRs

• gh-127349: Add check for correct resizing in REPL #127387
• [3.13] gh-127349: Add check for correct resizing in REPL (GH-127387) #129484
• [3.13] gh-127349: Add check for correct resizing in REPL (GH-127387) #129485