Traceback with --pdb refers to previous `pdb.set_trace()`

[blueyed]

Given t/test_pdb_offset.py:

def raises():
    raise Exception('outer')


def test_pdb_offset():
    __import__('pdb').set_trace()
    print(1)

    raises()

Running pytest t/test_pdb_offset.py --tb=short --pdb result in:

==================================== test session starts ====================================
platform linux -- Python 3.6.4, pytest-3.4.1.dev51+gb486e129, py-1.5.2, pluggy-0.6.0
rootdir: …/Vcs/pytest, inifile: tox.ini
collected 1 item                                                                            

t/test_pdb_offset.py 
>>>>>>>>>>>>>>>>>>>>>>>>>> PDB set_trace (IO-capturing turned off) >>>>>>>>>>>>>>>>>>>>>>>>>>
> …/Vcs/pytest/t/test_pdb_offset.py(7)test_pdb_offset()
-> print(1)
(Pdb) c
1
F
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> traceback >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
t/test_pdb_offset.py:7: in test_pdb_offset
    print(1)
t/test_pdb_offset.py:2: in raises
    raise Exception('outer')
E   Exception: outer
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> entering PDB >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
> …/Vcs/pytest/t/test_pdb_offset.py(2)raises()
-> raise Exception('outer')
(Pdb) c
                                                                                      [100%]
================================== short test summary info ==================================
FAIL t/test_pdb_offset.py::test_pdb_offset

Notice the first entry in the traceback (t/test_pdb_offset.py:7), which refers to the line after the pdb.set_trace(), but it should be the line where raises gets called.

pytest 3.4.1.dev51+gb486e129.

[blueyed]

(I can see this being useful as-is in some way, since it gets used when going up/down also inside pdb then.
pdbpp displays a -> for the line after the set_trace, and >> for the line where the exception is coming through.)

[blueyed]

This is a Python issue.
A PR to fix this is being evaluated at https://bugs.python.org/issue24565 / python/cpython#6233.

Test script:

import sys
import traceback


def f():
    print(1)
    if len(sys.argv) > 1:
        __import__('pdb').set_trace()
    print(2)
    raise Exception()


try:
    f()
except Exception as exc:
    print(exc)
    t = sys.exc_info()[2]
    if hasattr(t, '__traceback__'):
        assert t == exc.__traceback__
    traceback.print_tb(t)
    assert t.tb_lineno == 14, 'tb_lineno is off: %s' % t.tb_lineno
    assert t.tb_next.tb_lineno == 10, 'tb_next.tb_lineno is off: %s' % (
        t.tb_next.tb_lineno)

I think it could be addressed / fixed in pytest already in a similar way like pdbpp remembers the correct location: https://github.com/antocuni/pdb/blob/b7e789b836340ecbc131e26f8fd93d74fe652297/pdb.py#L234-L239.