Passthrough removal fails for sliced probes

def go(do_bug):
    with nengo.Network() as model:
        a = nengo.Ensemble(1, 1, label="a")
        passthrough = nengo.Node(size_in=1, label="passthrough")
        b = nengo.Ensemble(1, 1, label="b")

        nengo.Connection(a, passthrough)
        nengo.Connection(passthrough, b)

        p = nengo.Probe(passthrough[0] if do_bug else passthrough)

    with nengo_loihi.Simulator(model, remove_passthrough=True) as sim:
        pass

go(False)
go(True)

AssertionError                            Traceback (most recent call last)
<ipython-input-1-bbe32de37e3c> in <module>()
     21 
     22 go(False)
---> 23 go(True)

<ipython-input-1-bbe32de37e3c> in go(do_bug)
     17         p = nengo.Probe(passthrough[0] if do_bug else passthrough)
     18 
---> 19     with nengo_loihi.Simulator(model, remove_passthrough=True) as sim:
     20         pass
     21 

~/CTN/nengo-loihi/nengo_loihi/simulator.py in __init__(self, network, dt, seed, model, precompute, target, progress_bar, remove_passthrough)
    328             node_neurons=self.model.node_neurons,
    329             node_tau=self.model.decode_tau,
--> 330             remove_passthrough=remove_passthrough,
    331         )
    332         network = self.networks.chip

~/CTN/nengo-loihi/nengo_loihi/splitter.py in split(net, precompute, node_neurons, node_tau, remove_passthrough)
    144 
    145     # --- Step 5: place probes
--> 146     place_probes(networks)
    147 
    148     # Commit to the moves marked in the previous steps

~/CTN/nengo-loihi/nengo_loihi/splitter.py in place_probes(networks)
    484     for probe in networks.original.all_probes:
    485         target = base_obj(probe.target)
--> 486         networks.move(probe, networks.location(target))
    487 
    488 

~/CTN/nengo-loihi/nengo_loihi/splitter.py in move(self, obj, target, force)
     99         if not force:
    100             assert obj not in self, "already moved"
--> 101         assert target in self.targets, "invalid target"
    102         logger.debug("Moving %s to %s", obj, target)
    103         if obj in self.adds:

AssertionError: invalid target

The bug does not happen when remove_passthrough=False.

I believe the fix is to change this line: https://github.com/nengo/nengo-loihi/blob/1517915baa1b0200e5241ba55a65e9d0bc09bff8/nengo_loihi/passthrough.py#L217

so that ObjView are resolved into their underlying base objects (as done in the splitter). Note the other base_obj calls are okay, because they all use pre_obj and post_obj which already resolve the ObjView.

Note this issue is somewhat independent of #205, as the latter bug occurs even when remove_passthrough=False.

nengo / nengo-loihi

Passthrough removal fails for sliced probes #206