Cannot convert channel to list in DSL2

[jamesbaye]

Bug report

Expected behavior and actual behavior

Cannot convert channel to list in DSL2.

Steps to reproduce the problem

ch = Channel.of(1,2,3).toList().val[0] # returns 1

nextflow.enable.dsl = 2
ch = Channel.of(1,2,3).toList().val[0] # hangs indefinitely

Environment

• Nextflow version: 21.04.3
• Java version: 1.8.0_282
• Operating system: CentOS Linux release 7.9.2009
• Bash version: 4.2.46(2)-release

Additional context

We are interested in unit testing some internal channel creation methods, and would like to investigate channel contents as a list. Currently this bug is stopping us from writing those unit tests.

[pditommaso]

This is by design, you are expected to use the value returned by toList

[jamesbaye]

@pditommaso Do you mean by passing the channel as an input to a process? Is there any other way that can avoid the overhead of creating/queuing a process?

[pditommaso]

Use an operator eg map or subscribe

[jamesbaye]

Thanks @pditommaso. Resolved, I didn't realise I could add assert statements inside subscribe. Was able to test everything from within subscribe.