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Re: [libvirt] [PATCH 00/11] Make auto completion better

On Tue, Nov 07, 2017 at 01:22:48PM +0100, Michal Privoznik wrote:
After initial RFC [1] I had some time to work on this and here is
the result.

What's implemented?
Auto completion for both interactive and non-interactive

Known limitations
Currently, just options completers work. I mean, to bring up list
of domains you have to:

 virsh # start --domain <TAB><TAB>

Doing bare:

 virsh # start <TAB><TAB>

brings up list of --options. I am working on this meanwhile. But
one can argue that having to use --option is not that much of a
problem since we have good completion now.

The other known limitation - and actually room for others to join
and help - is missing completers. I mean, the last 3 patches give
an example how to do that. But that is still very few. We need
more completers.

How does this work?
The basic idea is simple, when defining opts for command two new
struct members can be set:

    {.name = "mac",
     .type = VSH_OT_STRING,
+     .completer = virshDomainInterfaceCompleter,
     .help = N_("MAC address")

@completer is the callback that is used when user wants to bring
up list of possible strings. @completer_flags can then be used to
refine return value of @completer. In this specific example,
virshDomainInterfaceCompleter() brings up list of interfaces for
given domain. It tries to return /interface/target/@dev but if
not found (e.g. because domain is not running),
/interface/mac/@address is returned otherwise. However, in one
specific case we are interested only in MAC addresses (regardless
flag is specified which alters @completer behaviour.

For non-interactive virsh/virt-admin there's
tools/bash-completion/vsh script which does no more than calling:

 $1 complete $USER_INPUT

(where $1 is name of the binary user intents to run).

How to test this?

Interactive completion should work out of the box. Just make sure
you're connected. Completers don't connect! You certainly don't
want ssh's 'Password:' prompt show on <TAB><TAB>, do you?
Non-interactive completers do connect, but in order to avoid any
password prompts, /dev/stdin is closed before anything else is
done. In order to test it, just:

 libvirt.git $ source tools/bash-completion/vsh

Now, bash completion should work:

 libvirt.git $ ./tools/virsh -c qemu:///system start --domain <TAB><TAB>

So if I do this, it works, but if I copy it where it is supposed to be installed
it doesn't for some reason.  I haven't dug into that, I don't even know where to
start, probably.  Also it is very possible that it's my fault.

I also found one more thing, but that's only easy to fix in few cases.  If you
type 'virsh start --domain fedora <TAB><TAB>' then one of the strings it offers
is '--domain'.  It'd be nice to have that filtered out.  Not needed for ACK,
though.  Just an idea for you.

Apart from that it looks sane, so ACK to the general concept, I would just
change 2/11 as written in the reply, drop (or completely replace) 3/11 and
instead do the '-qq' thing.  And of course adjust other code depending on that.
I'd ACK the rest, I would just like to have the middle-of-the-command completion
working too so it doesn't confuse people.

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