fix(interop.py): override instead of append to row[server]

[mxinden]

Previously when calculating each cell of the measurements result table, instead of always setting a cell, a cell would be appended in case one already existed. Appending a cell to another doesn't make sense in this context. In addition this code also errors, given that on the first cell row[server] += results in a KeyError.

 Traceback (most recent call last):
  File "run.py", line 168, in <module>
    sys.exit(main())
  File "run.py", line 150, in main
    return InteropRunner(
  File "/home/runner/work/quic-go/quic-go/quic-interop-runner/interop.py", line 529, in run
    self._print_results()
  File "/home/runner/work/quic-go/quic-go/quic-interop-runner/interop.py", line 243, in _print_results
    row[server] += "\n".join(results)
KeyError: 'quic-go-latest'

See e.g. https://github.com/quic-go/quic-go/actions/runs/8159188951/job/23046885072.

This commit fixes the above simply by setting the cell, not appending it for the case where one already exists.

Bug introduced in #355

[marten-seemann]

I'm not sure I understand what's going on here. As far as I can see, this was not introduced in #355, was it?

https://github.com/quic-interop/quic-interop-runner/pull/355/files#diff-a1f0ac428938a846f118f59aa8e2e66b90bff7b498b928204eb3bfcb41f1f528L228

[mxinden]

Before #355 it was:

row += ["\n".join(results)]

This adds to the row itself. The row is initialized to row = [client] beforehand, thus += is fine.

After #355 it was:

row[server] += "\n".join(results)

This adds to the cell (i.e. row[server]) within the row. The row is initialized to rows.setdefault(client, {}). But instead of the row, the cell (i.e. row[server]) is accessed. The cell might not be initialized and thus the +=, when retrieving the existing value before adding the new value, will run into a KeyError.

Does that make sense @marten-seemann?

[marten-seemann]

Thanks for the detailed explanation!

[WesleyRosenblum]

Something still seems broken: https://github.com/quic-interop/quic-interop-runner/actions/runs/8526238616/job/23355310162#step:17:31

[mxinden]

Thank you @WesleyRosenblum for spotting this. Should be fixed with #380.