__tracebackhide__ can retain hidden frames sharing a source location in ExceptionGroup tracebacks #14940

Description

When two traceback frames come from the same filename and line number, pytest can keep a frame marked with __tracebackhide__ = True in an ExceptionGroup traceback.

This can happen whenever distinct traceback entries share the same source location but have different __tracebackhide__ values. Recursion provides a simple reproducer.

Minimal example

def fail(number):
    __tracebackhide__ = number == 1

    if number == 0:
        raise ValueError("boom")

    fail(number - 1)


def test_failure():
    try:
        fail(2)
    except ValueError as error:
        raise ExceptionGroup("failure", [error]) from None

Run:

pytest -q test_example.py

Actual result

The relevant part of the nested traceback contains the recursive line twice:

File "test_example.py", line 7, in fail
    fail(number - 1)
File "test_example.py", line 7, in fail
    fail(number - 1)
File "test_example.py", line 5, in fail
    raise ValueError("boom")
ValueError: boom

Expected result

The calls have different __tracebackhide__ values:

fail(2) -> visible
fail(1) -> hidden
fail(0) -> raises ValueError

The fail(1) frame should be removed, so fail(number - 1) should appear only once. The equivalent traceback without the ExceptionGroup wrapper already behaves correctly.

Cause

_filter_tracebackexception() currently identifies filtered frames using (filename, line number). These values identify a source location, but not an individual occurrence in a traceback. A visible frame can therefore also retain a hidden frame from the same location.

This matching was added in #14649 for #14036. This report covers the remaining case where separate traceback frames share one source location.

Environment

• pytest main at 28549a5f6b82bc916bb2ec5cb9fbfffe9b79fc66
• Python 3.12.13
• Red Hat Enterprise Linux 9.8