Last night I learned how to convince vim that ! and ? are part of a keyword. This is awesome, because both those characters are valid characters for method names in Ruby. In particular, it now means that when I hit ctrl-] with my cursor in a method name containing a !, it will take me to the correct method definition. Let’s take an example, with a couple of methods on a User model:

Class User
  def invite(message)
    InvitationMailer.invitation(message).deliver_later
    @invited = true
  end

  def invite!(message)
    invite(message)
    save!
  end
end

and elsewhere, I have some code in a controller:

class UsersController < ApplicationController
  def invite
    @user.invite!(params[:message])
  end
end

With my cursor at the underscore on @user.in_vite!, I can hit ctrl-] and it will take me to the method definition of the keyword under the cursor. Prior to making last night’s discovery, vim would have determined that the keyword was invite, and it would have searched the ctags file for a match. Invariably, it would have decided that the closest match was the one in the same file, so it would take me to the method definition for the invite controller action — just where I already was.

The first thing I wanted to double check was to see that ctags was correctly storing the method names. In vim, you can jump directly to a tag definition with the :ta[g] command. This will accept a string or a regular expression of the tag we want to jump to. I tried jumping with :tag invite! and, sure enough, it takes me to the right definition, so the tags are being generated with the right method names, and vim is happy enough to accept them as identifiers. That’s not the problem then.

So, it would appear that the problem is with how vim determines the keyword we’re searching for based on the current cursor position. In other words, how does vim take the line @user.in_vite!(params[:message]) (with the cursor at the _) and determine that the keyword we’re looking to find the definition for is invite? And how do we change it so that it picks up the correct keyword, invite! instead?

At this point, I figured that what constitutes a keyword is probably language-specific, so I went down a rabbit hole of digging through the Ruby syntax file, seeing how it parsed and syntax highlighted various elements of a Ruby source file. Wow, that’s complex! However, it already correctly understands that ? and ! are valid characters in a method name, so that led me to believe vim wasn’t using syntax information to figure out what constitutes a keyword.

Eventually, I resorted to digging through the help files for the word ‘keyword’ and came across the option iskeyword. It transpires that this contains a list of the ASCII characters that are considered to be part of a keyword. The documentation here mentions that keywords are used in many commands, including ctrl-]. It also hints that they can be changed per file type (e.g. help files consider all non-blanks except for *, " & | to be part of a keyword). The default list of characters is @,48-57,_,192-255 which is:

• @ is all the characters where isalpha() returns true, so it’s a-z, A-Z and various accented characters.

• 48-57 are the ASCII digits 0-9.

• _ is the literal underscore character.

• 192-255 are the extended ASCII codes (accents, ASCII art symbols, that kind of thing).

So we can see that ! and ? are excluded from the list. I added them in to my current vim session with:

:set iskeyword=@,!,?,48-57,_,192-255

Then I tested it out by placing my cursor over @user.invite! and, sure enough, ctrl-] took me to the method definition! I did a little Snoopy dance at this point, but it was OK, because there was nobody else in the house. ;-)

It occurs to me that the definition of a keyword is language specific, so in order to make the configuration permanent, I’ve added the following to my ~/.vimrc:

autocmd FileType ruby set iskeyword=@,!,?,48-57,_,192-255

Restart vim to double check and yes, it’s now considering invite! and password_required? to be keywords. Winning!

Now that I’ve discovered the trick to tell vim what constitutes a keyword, I’m wondering a couple of things. Firstly, are there any other characters that should be part of a keyword in Ruby that aren’t included in the new list? And secondly, what other languages could do with their iskeyword being set to something different?