Bug report

Bug description:

Functions in the traceback module such as format_exc() fail when linecache.getlines() returns a comment or other incorrect source. The following fails with an IndexError: list index out of range exception raised in the format_exc() call.

import linecache
import traceback

pseudo_filename = 'pseudo filename'
src = '1/0'
co = compile(src, filename=pseudo_filename, mode='exec')
linecache._register_code(pseudo_filename, '# a comment', pseudo_filename)
try:
    exec(co)
except Exception as exc:
    lines = traceback.format_exc()

I know linecache.._register_code() is not public and code that does something like this is buggy, but the traceback module is used to report bugs and shouldn't fail itself.

The fix is probably to check the len(tree.body) in StackSummary._should_show_carets() in traceback.py before accessing tree.body[0]

CPython versions tested on:

3.13

Operating systems tested on:

No response