Support searching without automatically setting input

[dandavison]

Fixes https://github.com/bbatsov/helm-projectile/issues/32

This PR makes a backwards-compatible change that allows the user to call helm-projectile-grep and helm-projectile-ack without having the input set automatically.

I wrote the reasoning for this change in #32. I'm going to paste that here.

---

helm-projectile-grep automatically uses the current symbol at point (if any) as input. This means that if I think of a thing to search for, and don't pay attention to where my cursor is, I find myself in one of two states:

1. minibuffer already has some input; I need to delete it before entering my search term
2. minibuffer is empty

I think that it would be useful to provide a way to be certain that you will be in state 2: i.e. a way for the user to say: "regardless of where my cursor might be, do not seed my search with anything, I just want to type it in".

I'm new to these libraries, but, "I just want to type it in" seems to be the contract that the helm-*-grep-* functions offer. However, helm seems not to offer the thing-at-point or current-region-contents functionality at all, so I suggest that helm-projectile should offer all three versions.

---

This PR does not change the default behavior of helm-projectile. A separate question which could be discussed in future issues/PRs is what the default behavior of helm-projectile should be: helm doesn't default to setting input automatically, so there is an argument that helm-projectile should follow suit.

With this change a user can define custom functions that change the behavior:

(defun my-helm-projectile-grep (&optional use-input)
  (interactive "P")
  (helm-projectile-grep nil (not use-input)))

(defun my-helm-projectile-ack (&optional use-input)
  (interactive "P")
  (helm-projectile-ack nil (not use-input)))

[dandavison]

@bbatsov do you have time to consider this PR?

[bbatsov]

Probably this should be a defcustom instead of an extra param. Seems pretty doubtful to me that anyone but you would define the custom functions you mentioned (because nobody would figure out this is possible).

[bbatsov]

@dandavison ping :-)

[dandavison]

Thanks for the reminder @bbatsov! I've changed the PR to use a defcustom as you suggested: see helm-projectile-set-input-automatically. Feel free to choose a better name.

I've made this PR 100% behavior-preserving. Note that there was a pre-existing slight inconsistency in the behavior of helm-projectile-ag (no auto-input by default) vs. helm-projectile-ack and helm-projectile-grep (auto-input by default). This is documented in the defcustom text. I'll defer to you on whether we want to change any of the default behavior in subsequent PRs.

[dandavison]

@bbatsov ping, we'll get this done eventually!

[bbatsov]

Indeed. :-)