add subcommand tab completion for data plugin commands

[DropD]

I am not sure if this should be in the release but it makes the recently added data plugin commands more user friendly, usage example:

$ verdi data mydata <Tab>
export list show
$ verdi data mydata ex<Tab> # will complete to export

The way it works is by inserting code in the current completion system that recognizes click commands and treats them specially:

All click type commands are actually invoked by invoking aiida.cmdline.commands.verdi (a click group).
Therefore I had to use sys.argv in the completion code to find the class of the actual subcommands in order to create a completion function for it using the .listcommands functionality that all click.MultiCommands have.

It may look hackish but I don't see a much cleaner way without changing more about how the current completion system works.

[DropD]

@ltalirz Feel free to reassign to v0.12.0 If you think this non-essential.

[DropD]

It is worth mentioning that the previous behaviour was something like

$ verdi data mydata <Tab>
Usage: ...
...
Exception: no command "completion".
$ 

[DropD]

Also, please let me know if you can think of a way to test tab completion on travis.

[giovannipizzi]

Thanks, very good! I only added a couple of small comments/questions. It works ok for 'old' commands, I couldn't test with click commands, are there any in aiida_core that would trigger the new code, or they are all in plugins?

[giovannipizzi]

Could you add a comment explaining why you take out the first 3 args and what is the content of sys.argv[4:len(sys.argv)-1]?

[DropD]

Requested info is in the docstring of the function now.

[giovannipizzi]

How does this command work? Is this a replacement for the Completion class in verdilib/when is this called? If this is the case (i.e. 'verdi completion' calls now this and not directly the Completion() class, , maybe we should move the Completion class out of verdilib, where it is automatically discovered (I'm assuming the autodiscover of the classes in verdilib is still active).

[giovannipizzi]

BTW, for the testing, one could try to use an approach similar/adapted from the one used in this package: https://github.com/kislyuk/argcomplete/blob/master/test/test.py

[DropD]

There are no commands with which to test this currently in core. I used a data command i am developing in aiida-vasp to test it.

[DropD]

Rebased on release_v0.11.0 and adjusted the base of the PR.

[giovannipizzi]

Great!