[Bug] Running a cell again before it finishes

[benlubas]

Description

Specifically by overwriting the cell with a new one in the same place.

This causes:

• assertions about cell status not being DONE to fail
• the next run cell will render output from the cell that we ran twice (this one is really weird)
• possibly others?

Reproduction Steps

Run a cell like:

import time
for _ in range(100):
  print("-", end="")
  time.sleep(0.1)

and while it's still running, run it again by running the same code, so that it creates an overlapping cell (and therefore deleting the old one). Then run a new cell with different output, and see the same output from before.

Expected Behavior

Not that

[benlubas]

I think the best way to prevent this would be to error (notify the user) when trying to create a cell that overlaps a currently running cell.

The alternative is interrupting the cell which might be painful for people that accidentally press their run binds, or don't realize that a cell has been running.

Additionally, some kernels can't be interrupted (ie. rust's evcxr. though this might be the only one), so any solution that involves interrupting kernels won't work in all cases.