set the font before computing the distance between the line numbers and the real text. add an option to the general pane to enable line numbers

collects/drracket/private/main.rkt

@@ -316,6 +316,18 @@
      (make-check-box 'drracket:open-in-tabs 
                      (string-constant open-files-in-tabs)
                      editor-panel)
+     (make-check-box 'drracket:show-line-numbers?
+                     (string-constant show-line-numbers)
+                     editor-panel
+                     (lambda (value)
+                       (define (drracket:frame? frame)
+                         (and (is-a? frame top-level-window<%>)
+                              (is-a? frame drracket:unit:frame%)))
+                       ;; is it a hack to use `get-top-level-windows' ?
+                       (define frames (filter drracket:frame? (get-top-level-windows)))
+                       (when (not (null? frames))
+                         (send (car frames) show-line-numbers! value))))
+
      (make-check-box 'drracket:show-interactions-on-execute 
                      (string-constant show-interactions-on-execute)
                      editor-panel)

collects/framework/private/text.rkt

@@ -3902,6 +3902,7 @@ designates the character that triggers autocompletion
             (define-values (x y) (send dc get-origin))
             (set! old-origin-x x)
             (set! old-origin-y y)
+            (setup-dc dc)
             (define-values (font-width font-height baseline space)
                            (send dc get-text-extent "10000"))
             ;; add an extra 0 so it looks nice