Autocomplete Github issue numbers from Vim using a custom completion function, Ruby and the Github API.

issue-completion.vim

function! MyOmniFunc(findstart, base)
  if a:findstart
    let existing = matchstr(getline('.')[0:col('.')-1],'#\d*$')
    return col('.')-1-strlen(existing)
  endif
  ruby << EOF
  require 'open-uri'
  require 'json'

  def issues(repo, token)
    JSON.parse(
      open(
        sprintf('https://api.github.com/repos/%s/issues', repo),
        http_basic_authentication: [token, 'x-oauth-basic']
      ).string
    ).map do |issue|
      sprintf(
        %Q|{ "word": "#%s", "menu": "%s" }|,
        *issue.values_at('number', 'title')
      )
    end
  end

  iss = issues('USERNAME/PROJECT', 'TOKEN')
  VIM.command("return [#{iss.join ','}]")
EOF
endfunction

set omnifunc=MyOmniFunc