Breakpoint in cell with leading empty lines may be ignored

[fcollonval]

If a cell starts with empty lines, they are cleanup as part of the code transformation. This result in breakpoint that can be missed as the number of lines executed will be smaller than the breakpoint line number.

For example,

def f(a, b):
    return a + b
f(2, 3)

Setting the breakpoint on the last line is not working

Xref: jupyterlab/jupyterlab#11532

This removes the leading_empty_lines cleanup transform when a debug session is active.

[fcollonval]

pinging @Carreau could you please have a look at this PR? I'm not very confident to turn off one of the default transformation applied by IPython.

[fcollonval]

The error on Python 3.10 seems legit.

[fcollonval]

Actually the debugger with Python 3.10 is much more broken than with Python 3.9. But I can't yet figure out what is going on.

[fcollonval]

I propose to skip the new test for Python 3.10 for now. And tackle the issue related to Python 3.10 in a separate PR.

[Carreau]

I have no objection to have this as a workaround, we can make the transformer have an enabled/disabled flag in IPython itself to make it less brittle to index positions.

[fcollonval]

Thanks @Carreau

This is ready for review.

[blink1073]

Thanks!