I think the noise of combining what is usually on multiple lines (via semicolons) inhibits clarity here.  What do you think about using a more normal code layout like this?

``` ruby
class Foo
  def bar
    RSpec.deprecate "Foo#bar"
  end
end
```

Alternately, if you don't want all 5 lines, you could just define it as a top-level method directly on main, and then call it from the example below.  That'd cut it down to 3 lines.