Figure if a resource exists or not in Chef before notifying it

check_resource.rb

resource_not_found = {}
begin
  resources('ruby_block[my-resource-supposed-to-exist]')
rescue Chef::Exceptions::ResourceNotFound
  resource_not_found['ruby_block[my-resource-supposed-to-exist]'] = true
end

template '/etc/my/template.conf' do
  source 'template.conf.erb'
  mode '640'
  notifies :run, 'ruby_block[my-resource-supposed-to-exist]' unless resource_not_found['ruby_block[my-resource-supposed-to-exist]']
end

Inspired by your code, I wrote the following:

resource_exists = proc do |name|
  begin
    resources name
    true
  rescue Chef::Exceptions::ResourceNotFound
    false
  end
end

# Use:
template '/etc/my/template.conf' do
  source 'template.conf.erb'
  mode '640'
  notifies :run, 'ruby_block[my-resource-supposed-to-exist]' if resource_exists['ruby_block[my-resource-supposed-to-exist]']
end

I suspect that approaches like these aren't the most Chef ways to code this, but I'm not sure what would be a better solution. A library sounded like a good option, but then code is run in a different lexical scope, and that brought about more complexity, so I just used local variables.