company-mode: no completions found

I am new to emacs (long-time vim user). Specifically, I am using doom-emacs.

Doom is supposedly set up to use company-mode for auto completion, but I have not gotten it to work. I have the following source code:

class CompleteUserBankruptcyJob < ApplicationJob
  queue_as :default

  def perform(user)
    CompleteUserBankruptcy.call(user)
  end
end

If I type in def perfo, I would expect company to suggest perform. However, it does not suggest anything at all. If I manually trigger suggestions via C-SPC, it says "No completion found". Finally, if I run company-diag in the buffer, I get the following information:

Emacs 27.1 (x86_64-apple-darwin18.7.0) of 2020-08-12 on builder10-14.porkrind.org
Company 0.9.13

company-backends: (company-capf company-yasnippet)

Used backend: company-yasnippet
Major mode: ruby-mode
Prefix: nil
Completions: none

I have no idea how to debug further. If it is any help, I have my personal configuration files in this repo, but I have not modified any company-mode related settings, so it should all be using the default from doom-emacs, which for company I believe are located here. Finally, I believe that the list of backends is not being set correctly in ruby major mode (and may be failing in other modes as well), given the references to company in this file.