Clarify that filtering by prefix is not required in completers

[kislyuk]

See #137

[haifengkao]

really?

argcomplete.autocomplete(parser, validator=lambda x, y: True)
will not show anything.

I have to use
argcomplete.autocomplete(parser, validator=None)
for argcomplete to work

[haifengkao]

The problem seems to be related to zsh.
output_stream.write('/usr/hello'.encode(sys_encoding))
only works if the prefix of '/usr/hello' matches the suffix in the terminal

[evanunderscore]

I feel like the choices completer (and probably the others too) should not filter their results and defer to the validator to do the filtering. As it stands, if I want to do something like case-insensitive completion, I have to override the choices completer because the results are already filtered before they get to the validator. Or am I misunderstanding the purpose of the validator?

[kislyuk]

@haifengkao, it would be really awesome if a test could be added for this behavior. I'd like to create a pexpect test that would verify completions end-to-end in bash and zsh. Do you want to help?

@evanunderscore, the choices completer is presented as an example. The validator was added to this architecture after I first designed it, so I'm treating it as a general purpose filtering step. One of its functions is to filter the completions by prefix. The completer may also do so, for example if filtering will reduce the amount of work done (like when requesting completions from a remote API). Case insensitive completion is not generally supported. If you want it supported, please open another issue. We'll need to update the docs, think about how to communicate case insensitivity to completers, and add a CaseInsensitiveValidator.

[haifengkao]

@kislyuk sure. what do you need?

[kislyuk]

A test for the zsh behavior that you described (positive and negative test assertions). You may have to modify travis.yml to get zsh and pexpect installed.

[haifengkao]

The current tests are pure python and they don't involve the shell at all.
Do you want me to set up a new test framework for you?

[kislyuk]

We would need a new test case that uses pexpect. I would like to have it added in a new class in test/test.py.

[haifengkao]

I was doing a little research (http://www.zsh.org/mla/users/2013/msg00612.html).
Zsh has its own filtering system, which can be turned off by compadd -U. However, the link above suggests this -U option is not available in bash compatibility mode.

[evanunderscore]

Assuming zsh is sufficiently covered by #10 and #141.