Add support for --passthr{u,ough} flag

[zx8]

After reading this comment on HN, I thought it'd be neat to add support for the --passthrough / --passthru flag in ripgrep as well.

Thoughts?

[okdana]

I was thinking about that myself. I personally think it's easier to do it the way i mentioned in that thread, but it seems like some people are quite passionate about it, and it would be very trivial to add a flag that wraps the pattern in ^|(?:...), the way we do with -w and -x. (At least, that's the method that first comes to mind, because it's easy and i have experience with it.)

[BurntSushi]

I'm kind of meh on it, but I don't feel strongly enough to reject it outright.

ag spells it --passthrough while ack spells it --passthru. How should ripgrep spell it? o_0 I suppose we could just accept both.

I like @okdana's suggested implementation.

[okdana]

If it were me i think i'd make it --passthru, with --passthrough as like a hidden alias. Can't recall if Clap supports that tho

[kbknapp]

Can't recall if Clap supports that tho

It does 😉 (You can also make it visible so it's findable in the help output)

[BurntSushi]

@jzinn both are supported. Ripgrep has no specific goal to be "formal."

Please drop this. It's a waste of time.