assert sources != null;
Set<Source> opposites = Sets.create();
for (FlowBlock.Input input : target.getInputs()) {
for (FlowBlock.Connection conn : input.getConnections()) {
FlowBlock.Output upstream = conn.getUpstream();
Source source = sources.get(upstream);
assert source != null;
opposites.add(source);
}
}
target.resolveSources(opposites);