Fix follow-mouse clicks on undraggable mode/header lines.

* mouse.el (mouse-drag-line): Even if the line is not draggable,
keep reading until we get the up-event anyway, in order to process
the up-event for mouse-1-click-follows-link.

Fixes: debbugs:12971

2 files changed, 13 insertions, 7 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 431f45c3695..04aa1dc0216 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,9 @@
+2012-11-24  Chong Yidong  <cyd@gnu.org>
+
+        * mouse.el (mouse-drag-line): Even if the line is not draggable,
+        keep reading until we get the up-event anyway, in order to process
+        the up-event for mouse-1-click-follows-link (Bug#12971).
+
 2012-11-23  Stefan Monnier  <monnier@iro.umontreal.ca>
 
         * emacs-lisp/bytecomp.el (byte-compile-file): Setup default value for
diff --git a/lisp/mouse.el b/lisp/mouse.el
index 61d70404bd6..60a3d390889 100644
--- a/lisp/mouse.el
+++ b/lisp/mouse.el
@@ -425,7 +425,7 @@ must be one of the symbols `header', `mode', or `vertical'."
                                    (frame-parameters frame)))
                         'right)))
          (draggable t)
-         event position growth dragged)
+         finished event position growth dragged)
     (cond
      ((eq line 'header)
       ;; Check whether header-line can be dragged at all.
@@ -457,7 +457,7 @@ must be one of the symbols `header', `mode', or `vertical'."
     ;; Start tracking.
     (track-mouse
       ;; Loop reading events and sampling the position of the mouse.
-      (while draggable
+      (while (not finished)
         (setq event (read-event))
         (setq position (mouse-position))
         ;; Do nothing if
@@ -472,7 +472,7 @@ must be one of the symbols `header', `mode', or `vertical'."
         ;;   - there is a keyboard event or some other unknown event.
         (cond
          ((not (consp event))
-          (setq draggable nil))
+          (setq finished t))
          ((memq (car event) '(switch-frame select-window))
           nil)
          ((not (memq (car event) '(mouse-movement scroll-bar-movement)))
@@ -480,15 +480,15 @@ must be one of the symbols `header', `mode', or `vertical'."
             ;; Do not unread a drag-mouse-1 event to avoid selecting
             ;; some other window.  For vertical line dragging do not
             ;; unread mouse-1 events either (but only if we dragged at
-            ;; least once to allow mouse-1 clicks get through.
+            ;; least once to allow mouse-1 clicks get through).
             (unless (and dragged
                          (if (eq line 'vertical)
                              (memq (car event) '(drag-mouse-1 mouse-1))
                            (eq (car event) 'drag-mouse-1)))
               (push event unread-command-events)))
-          (setq draggable nil))
-         ((or (not (eq (car position) frame))
-              (null (car (cdr position))))
+          (setq finished t))
+         ((not (and (eq (car position) frame)
+                    (cadr position)))
           nil)
          ((eq line 'vertical)
           ;; Drag vertical divider.