bug#20260: 24.4.1; Triple-clicking selects and deselects the line in weird situations

bug#20260: 24.4.1; Triple-clicking selects and deselects the line in weird situations

[Jorgen Schaefer]

Hello!
We came across a weird behavior in Emacs.

The graphical version (in X) will select a line if the mouse is
triple-clicked. Under certain situations, it will select but immediately
deselect the line again.

Reproduction:

Triple-click on any line in any buffer. Notice that Emacs selects the
whole line, and leaves it selected.

Evaluate the following code.

(defun repro-filter (fun beg end delete)
  (let ((string (funcall fun beg end delete)))
    (with-temp-buffer
      (insert "."))
    string))

(with-current-buffer (get-buffer-create "*Bug*")
  (set (make-local-variable 'filter-buffer-substring-functions)
       '(repro-filter))
  (insert "Hello, World!\n")
  (pop-to-buffer (current-buffer)))

Triple-click on the "World" in the *Bug* buffer. Notice that Emacs
selects the whole line only momentarily, and then deselects it again
immediately.

I expected the line to stay selected like without this piece of code.

This bug was not present in 24.3.

Regards,
Jorgen

bug#20260: 24.4.1; Triple-clicking selects and deselects the line in weird situations

[Stefan Monnier]

> Triple-click on the "World" in the *Bug* buffer. Notice that Emacs
> selects the whole line only momentarily, and then deselects it again
> immediately.

Indeed.  I though I had fixed this in Emacs-25 by making deactivate-mark
buffer-local, but I actually failed to adjust the C code accordingly.

The patch below seems to fix your test case.  Can you confirm it also
fixes your real use case?


        Stefan


diff --git a/src/fileio.c b/src/fileio.c
index d4e12cb..a6e7fbb 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -4165,7 +4165,7 @@ by calling `format-decode', which see.  */)
       Vdeactivate_mark = old_Vdeactivate_mark;
     }
   else
-    Vdeactivate_mark = Qt;
+    Fset (Qdeactivate_mark, Qt);
 
   emacs_close (fd);
   clear_unwind_protect (fd_index);
diff --git a/src/insdel.c b/src/insdel.c
index 80650be..22c2bcc 100644
--- a/src/insdel.c
+++ b/src/insdel.c
@@ -1846,7 +1846,7 @@ prepare_to_modify_buffer_1 (ptrdiff_t start, ptrdiff_t end,
       = call1 (Fsymbol_value (Qregion_extract_function), Qnil);
 
   signal_before_change (start, end, preserve_ptr);
-  Vdeactivate_mark = Qt;
+  Fset (Qdeactivate_mark, Qt);
 }
 
 /* Like above, but called when we know that the buffer text

bug#20260: 24.4.1; Triple-clicking selects and deselects the line in weird situations

[Vasilij Schneidermann]

The patch does indeed fix the test case for me, but the real use case
stays unchanged.

Meanwhile, I've found a way to make the test case pass on 24.4,
let-binding `deactivate-mark`:

(defun repro-filter (fun beg end delete)
  (let ((string (funcall fun beg end delete))
	deactivate-mark)
    (with-temp-buffer
      (insert "."))
    string))

(with-current-buffer (get-buffer-create "*Bug*")
  (set (make-local-variable 'filter-buffer-substring-functions)
       '(repro-filter))
  (insert "Hello, World!\n")
  (pop-to-buffer (current-buffer)))

This change makes triple-clicking "World" in the *Bug* buffer no longer
deselect it.  Why it is needed in 24.4, but not in 24.3 is beyond my
understanding of Emacs.

bug#20260: 24.4.1; Triple-clicking selects and deselects the line in weird situations

[Stefan Monnier]

> The patch does indeed fix the test case for me, but the real use case
> stays unchanged.

Hmm... Can you provide another recipe that still isn't fixed with the patch?

> Meanwhile, I've found a way to make the test case pass on 24.4,
> let-binding `deactivate-mark`:

Yes, that works around the problem, but it shouldn't be necessary in Emacs-25.

The workaround you use was needed in many places: deactivate-mark was
global, so modifying one buffer could end up deactivating the mark in
some unrelated buffer.  In Emacs-25, we've changed it to be
buffer-local, so modifications in one buffer should not affect the
activation of the mark in another any more.

> Why it is needed in 24.4, but not in 24.3 is beyond my
> understanding of Emacs.

I don't know either, actually.


        Stefan

bug#20260: 24.4.1; Triple-clicking selects and deselects the line in weird situations

[Jorgen Schäfer]

Hello.
At least for me, the patch fixes the problem in the original context
(Circe IRC buffers).
Thank you. But that means I'm out of the game for providing test
cases, I am afraid ...

Regards,
Jorgen

bug#20260: 24.4.1; Triple-clicking selects and deselects the line in weird situations

[Stefan Monnier]

>> The patch does indeed fix the test case for me, but the real use case
>> stays unchanged.

Since it fixes Jorgen's test case I installed the patch into master, and
I'm closing this bug.

> Hmm... Can you provide another recipe that still isn't fixed with the patch?

If/when you find another recipe to reproduce your problem, just make
a new bug report (or re-open this one).

Thank you,


        Stefan