Clarify readme

[tremby]

The readme says that git-grep will be used if present, otherwise ag, otherwise ack, otherwise regular grep.

Then the instructions say to install ag, and set g:grepprg to ag.
Then to install ack, and set g:grepprg to ack. But then why did I set it to ag? Which one should it be set to? Isn't the whole point to use git-grep first, then fall back to each alternative?

From looking at the code it seems the only reason to set that variable is if I do not want to the fallback behaviour.

[teoljungberg]

The fallback-behavior is only present if g:grepprg isn't set, as you said. So if you override that with your own grep-program you have decided that that's what you want. Both ag and ack work outside a git-repository, git-grep doesn't. That's why the fallback is there, and that's why it does not do any fallback if you have set your own grep-program

[tremby]

What if I want to use ag by default and fall back to ack or grep if it's
not there, for example if I'm on another server where I can't install them
ag or ack?

[teoljungberg]

That would require something like a linked-list to favor certain services over others, and I would rather not do that. Mainly due to personal opinions of people, I hesitated with having the fallback-behaviour due to the same reason. I just took what I wanted for myself

I don't see a good solution to this, sorry..

[tremby]

Well in that case I don't see the point in using your plugin and
configuring it to use a particular grepping program at all. Isn't it
identical to just setting the grepping command directly with a single line
in your vimrc?

Of course, I do see the point if a user's preferences are the same as your
own.

[teoljungberg]

The idea with the fallback was to provide a sane default to the user, and I don't see it as a problem if you specify a grep-command of your own - you have decided on that command.

Feel free to make a pull-request if you find out a solution to this

[teoljungberg]

@tremby would it work for you if you could specify your fallback?

[tremby]

I'm actually okay with your defaults: git, then ag, then ack, then grep.

I just remain confused about what the point of being allowed to specify g:grepprg is at all, since when specified it appears to function exactly the same as not having the plugin installed and specifying the regular vim option grepprg. So I suppose I'm suggesting removing the option entirely (if I'm right that it adds nothing) and perhaps, yes, allowing the fallback chain to be configured.

[teoljungberg]

@tremby What do you think of doing something like - https://github.com/teoljungberg/vim-grep/tree/configure-callback ?

[tremby]

I think that's more useful than the current behaviour.