Introduce triple bang syntax to remove triggers

[somini]

In a snippets file, snippet!!! foo will remove the trigger from the
current lookup for the current context. Load order still matters.

This is useful to override a series of triggers with different
descriptions, and turn that into a single trigger, so that you don't
have to choose.

Similar, but different to #214.

[somini]

Of course, this could be "solved" by forking the snippets repo, but #214 was solved in the same way of adding features to snipmate, so I think this is warranted.

[ajzafar]

@somini I'm not against merging this, but I want to make sure I understand the intention first. Can you provide a detailed scenario (ideally with some sample file structure and snippets) of what you're trying to achieve?

My understanding is that if you're editing, say, your personal cpp.snippets, you want to a) remove instances of snippets in, for example, your copy of the honza snippet repo's cpp.snippets but not those in the repo's c.snippets that may be imported as a result of extends or scope aliases; and b) be able to remove specific snippets based on their description. Part (a) needs to be tweaked to work with the override option. Part (b) seems inflexible to me. I'm thinking maybe we allow an optional regex to be specified to determine exactly which snippets are to be removed. What do you think?

[somini]

My use case when I created this was the following:
I'm using https://github.com/honza/vim-snippets unchanged.

https://github.com/honza/vim-snippets/blob/master/snippets/python.snippets#L94-L121
This file defines 3 different snippets for the "try" trigger. I wanted to override this and include a single one, so that expansion happens automatically. I don't want to affect other snippets with the try trigger.

https://github.com/honza/vim-snippets/blob/master/snippets/htmldjango.snippets#L41-L44
This file extends html. Both include the "for" trigger. In order for expansion to be automatic, I deleted the "for" trigger using this triple-bang syntax from the HTML snippets file ONLY, and keep the htmldjango intact.

As for your comments, the assumptions are correct:
a) I don't see how the override option changes the behaviour of this syntax. Do you mind ellaborate on that?
b) The regex idea is pretty good, so that you can have full control over what snippets to delete. I'll work on that ASAP.

[ajzafar]

@somini Sorry for the really late response! The format of the path argument to the SetByPath() function changes depending on the setting of the override option. With it on, path is of the form scope<space>description. With it off, it's of the form scope<space>uniq_path<space>description, where uniq_path is a hopefully unique substring of the runtime path from which the snippet came. I was thinking instead of spaces to delimit the two to three parts of the function argument, we could decide on a delimiter. Then we could have the snippet!! directive take an optional regex that matches the entire thing. That should hopefully meet your requirements while being as flexible as can be.

I'm hoping to spend more time on SnipMate in the coming weeks, so I can hopefully get this sorted once I finish up the work on #207.

[somini]

Rebased this onto the latest master.

[somini]

Rebased this onto the latest master.