How notebook run by line works
Notebook Run by line is very close to debugging a cell. The differences in the sequence diagram are highlighted below:
Differences are described below.
Instead of a DebugCellController, a RunByLineController is created. This class intercepts messages from the debugger differently than the DebugCellController does. This intercepting is done in the willSendEvent override.
In a run by line situation, the IP indicator is only supposed to step over lines in the cell. Internally this is done by doing a step into over and over. If the step into falls into another cell (or another module), the RunByLineController issues another step to continue until the IP indicator lands in the cell again.