GRC does not connect() blocks with no ports even though GR supports this

[kpreid]

Steps to reproduce:

1. Define a hierarchical block which has no input or output ports, but which has blocks that do some detectable work inside it.
2. Define a top block, in GNU Radio Companion, which contains this hierarchical block.
3. Run the generated top block; observe that nothing happens.

The generated code instantiates the hier_block (e.g. self.hier_block_no_ports_0 = hier_block_no_ports()) but does not connect it (e.g. self.connect(self.hier_block_no_ports_0), using the 1-argument form of the connect method), so the blocks within the hier block do not do anything. If I manually add the connect call then the self-contained graph within the hier block does execute.

Thus, GR supports this case but GRC does not. I propose that GRC be modified so that, if a block in a top/hier block has no ports, then a 1-argument connect call will be generated for it.

Compatibility considerations: As far as I know, this should not affect the behavior of existing correct programs; however, if for some reason a block is declared to GRC to have no ports but actually does have ports, this will cause a new runtime error (whereas the block would previously have been instantiated but otherwise ignored).

[dkozel]

Thanks for filing the issue. This seems like a clear and hopefully reasonably straightforward improvement to GRC!

[haakov]

I can take care of this. Note to self: Don't connect() blocks that don't have a make template

[haakov]

@kpreid I've added a PR: #3007

Can you please confirm that it fixes the bug?

[kpreid]

@haakov I attempted, but I'm currently having trouble building GR from source. Sorry. The code looks reasonable to me.