Re: [tim-janik/beast] BSE: fix undo problems that occur after removing a bus (#82)

[Tim Janik <notifications github com>]

For the sake of this discussion, we only need to do three things:

[...snip...] removing lots of symptom investigation [...snip...]

You never get to the root cause here, which is removal of connections without undo recording in the first place.

which we can summarize as the input/outputs of Bus-1 are disconnected in bse_container_uncross_undoable [1], due to this bse_bus_disconnect [2] fails and finally the undo step is not recorded in BusImpl::disconnect_bus [3]. The patch that I've proposed fixes this by ignoring the error code Error::SOURCE_NO_SUCH_CONNECTION in [3]. Note that this doesn't irgnore all possible errors, just specialcase the case that there was no connection.

• Why should an undo step be recorded for restoring a connection that doesn't exist in the first place?

Because the connection did exist, but was removed in [1].

No, you're just looking at one possible way and one possible time to call a function, a connection did not necessarily exist previously, and only if it did would it be valid to record an undo step.

• Also, with your code, calling disconnect_bus() repeatedly will record more and more undo steps, for a connection that's not existing and could have been restored at most only once anyway.

Honestly, I don't know the answer to this. Maybe the fix should go somewhere else, or if we want to keep this, we could add state to the bus that indicates whether the bus is connected or not (independantly of whether or not the channels are connected).

Thanks for tracing this down, a clear problem understanding is part of what's needed for a fix. As for the actual patch, we must make sure to only record undo steps when appropriate though like described earlier.

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