Fix point motion in cloned buffers

* src/thread.c (post_acquire_global_lock): Call
set_buffer_internal_2 instead of tricking set_buffer_internal_1
into resetting the current buffer even if it didn't change.  This
avoids bug#25165, caused by failing to record the modified values
of point and mark, because current_buffer was set to NULL.  Also,
don't bother re-setting the buffer if there was no thread switch,
as that just wastes cycles.
* src/buffer.c (set_buffer_internal_2): New function, with most of
the body of set_buffer_internal_1, but without the test for B
being identical to the current buffer.
(set_buffer_internal_1): Call set_buffer_internal_2 if B is not
identical to the current buffer.
* src/buffer.h (set_buffer_internal_2): Add prototype.

* test/src/thread-tests.el (thread-sticky-point): New test.

1 files changed, 11 insertions, 1 deletions

diff --git a/test/src/thread-tests.el b/test/src/thread-tests.el
index 4e7b052cba0..7261cda9fbb 100644
--- a/test/src/thread-tests.el
+++ b/test/src/thread-tests.el
@@ -221,8 +221,18 @@
     :group 'widget-faces))
 
 (ert-deftest thread-errors ()
-    "Test what happens when a thread signals an error."
+  "Test what happens when a thread signals an error."
     (should (threadp (make-thread #'call-error "call-error")))
     (should (threadp (make-thread #'thread-custom "thread-custom"))))
 
+(ert-deftest thread-sticky-point ()
+  "Test bug #25165 with point movement in cloned buffer."
+  (with-temp-buffer
+    (insert "Lorem ipsum dolor sit amet, consectetur adipiscing elit.")
+    (goto-char (point-min))
+    (clone-indirect-buffer nil nil)
+    (forward-char 20)
+    (sit-for 1)
+    (should (= (point) 21))))
+
 ;;; threads.el ends here