Can debugger forward "source" requests to debugpy?

[vidartf]

The current handler for "source" requests to the debugger is as follows:

https://github.com/ipython/ipykernel/blob/221dca63d7b2e2b8fea32bf8a101d07645fc9d3c/ipykernel/debugger.py#L427-L445

Intuitively, I would expect that the source request would be forwarded to debugpy, so that the more complete implementation of pydevd could handle the request. Some differences of that implementation:

• Both implementations tries direct file access first.
• pydevd then tries the linecache with the following comment:

  File might not exist at all, or we might not have a permission to read it, but it might also be inside a zipfile, or an IPython cell. In this case, linecache might still be able to retrieve the source.

• Finally, pydevd falls back to using the sourceReference supplied (which would previously be given on e.g. "module" events I think).

One of the advantages of the approach of pydevd is that it also is able to handle modules that are loaded from custom module loaders (zip file loader, DB loaders, web loaders, etc.). It would therefore be good if someone could write out why we're not simply forwarding the request to debugpy, and if there is a solid reason for it, maybe we could improve upon it so that we can still support the sourceReference field?

[vidartf]

(CC @JohanMabille )

[JohanMabille]

Hi @vidartf ,

Sorry for the late reply, but I have now the whole story ;)

When sending a Source request, you need to provide a sourceReference argument because of old adapters. The issue is that the sources of notebook cells are never loaded, the are created by the kernel which dumps the content in temporary files. Therefore, there is no sourceReference for them. Besides, specifying sourceReference: 0 in the sourceRequest does not work; debugpy does not find the source if you do so, even if you provide a Source argument with the right path.

Therefore it is required that the kernel handles the request when sourceReference is 0.