[issue42246] Implement PEP 626 -- Precise line numbers for debugging

[Mark Shannon]

Mark Shannon <mark at hotpy.org> added the comment:

Thanks Ned, that's really helpful. I'll go through those points:

Code after break/continue is no longer compiled.
    Expected

First line number of modules
    Expected

Except clause when no exception
    https://bugs.python.org/issue42634

Double loops (this also covers End-of-loop jumps, I think)
    https://bugs.python.org/issue42635

I want to merge https://github.com/python/cpython/pull/23743 before I fix any of the others, but here is a summary of what I think are the root causes.

if-break
    Exit block duplication does not preserve line number of jump to final block

Finally handling
    Combination of two things. Not preserving line numbers when performing jump-to-jump elimination and not marking try cleanup code as artificial.

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<https://bugs.python.org/issue42246>
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