Index: includes/form.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/form.inc,v
retrieving revision 1.432
diff -u -p -r1.432 form.inc
--- includes/form.inc	12 Feb 2010 15:11:29 -0000	1.432
+++ includes/form.inc	21 Feb 2010 22:03:45 -0000
@@ -1875,7 +1875,16 @@ function form_select_options($element, $
       else {
         $selected = '';
       }
-      $options .= '<option value="' . check_plain($key) . '"' . $selected . '>' . check_plain($choice) . '</option>';
+      // @todo See http://drupal.org/node/426056 about server-side enforcement
+      //   of #disabled. Until then, if an option is already selected, do not
+      //   disable it.
+      if (empty($selected) && !empty($element['#disabled_options']) && in_array($key, $element['#disabled_options'])) {
+        $disabled = ' disabled="disabled"';
+      }
+      else {
+        $disabled = '';
+      }
+      $options .= '<option value="' . check_plain($key) . '"' . $selected . $disabled . '>' . check_plain($choice) . '</option>';
     }
   }
   return $options;
@@ -2197,6 +2206,9 @@ function form_process_radios($element) {
           '#id' => drupal_html_id('edit-' . implode('-', $parents_for_id)),
           '#ajax' => isset($element['#ajax']) ? $element['#ajax'] : NULL,
         );
+        if (!empty($element['#disabled']) || (!empty($element['#disabled_options']) && in_array($key, $element['#disabled_options']))) {
+          $element[$key]['#disabled'] = TRUE;
+        }
       }
     }
   }
@@ -2403,6 +2415,9 @@ function form_process_checkboxes($elemen
           '#attributes' => $element['#attributes'],
           '#ajax' => isset($element['#ajax']) ? $element['#ajax'] : NULL,
         );
+        if (!empty($element['#disabled']) || (!empty($element['#disabled_options']) && in_array($key, $element['#disabled_options']))) {
+          $element[$key]['#disabled'] = TRUE;
+        }
       }
     }
   }
@@ -2570,6 +2585,9 @@ function form_process_tableselect($eleme
             '#ajax' => isset($element['#ajax']) ? $element['#ajax'] : NULL,
           );
         }
+        if (!empty($element['#disabled']) || (!empty($element['#disabled_options']) && in_array($key, $element['#disabled_options']))) {
+          $element[$key]['#disabled'] = TRUE;
+        }
       }
     }
   }