Step into from Python to C++ doesn't work if arguments are unpacked into function call

[vsfeedback]

This issue has been moved from a ticket on Developer Community.

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[severity:It bothers me. A fix would be nice] It seems that in a mixed-mode Python/C++ debugging session, while debugging a piece of Python code, stepping into a function whose implementation is in C++, this does not work if the arguments are unpacked into the function call.

Example:

fast_foo(1, 2, 3)  # works, I manage to step into the C++ code

args = (1, 2, 3)
fast_foo(*args)  # does not work, it instead steps over the function call

A work around seems to be to either set a break point in the C++ code, or to change the calling code:

args = (1, 2, 3)
fast_foo.__call__(*args)

For some reason, using the __call__ method seems to not suffer from the problem. However, both of these work arounds are not really satisfactory.

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Original Comments

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Original Solutions

(no solutions)

[int19h]

Likely due to code not keeping up with various possible step-in code flows in newer versions of Python.

[int19h]

Relevant code parts:

https://github.com/microsoft/PTVS/blob/421d001d433ab8f05b210dad10a54807af5ea6ff/Python/Product/Debugger.Concord/TraceManagerLocalHelper.cs#L220-L223

https://github.com/microsoft/PTVS/blob/421d001d433ab8f05b210dad10a54807af5ea6ff/Python/Product/Debugger.Concord/TraceManagerLocalHelper.cs#L539-L813

So basically there's some code path that handles the CALL_... bytecode opcodes that either doesn't go through any of these, or if it does, it doesn't set a breakpoint on some of the potential destinations.