Re: mouse-yank-primary and bug #7699

[David De La Harpe Golden <david@harpegolden.net>]

On 22/12/10 11:09, Eli Zaretskii wrote:

> What is still unclear to me (but not entirely relevant to the issue at
> hand in bug #7699) is why do we call x-get-selection at all, when
> x-get-selection-value returns nil?

(Bearing in mind that IMNHO mouse-yank-primary /shouldn't be/ calling 
the current w32 x-get-selection-value):

Remember that w32 x-get-selection-value follows the funny 
interprogram-paste-function protocol intended for kill-ring interactions 
that returns nil if the text has already been got. It _is_ w32's 
interprogram-paste-function after all!

So when you click mouse-2 on w32, you presently might get the clipboard, 
or you might get the emulated primary, depending on fairly complex 
(though deterministic) details of the interaction path leading up to the 
mouse-2 click. If you were to remove the call to x-get-selection on w32, 
you'd get the clipboard once (probably) and then nowt for subsequent 
clicks.

If you were to remove the call to x-get-selection-value that was 
inserted, on w32 you should get the emulated primary on all clicks if it 
is available, consistent with the function name "mouse-yank-primary", 
and bearing in mind it might or might not currently be being updated 
properly elsewhere on w32 (I haven't looked recently).

But wait - why does X11 now have and call a function called 
x-get-selection-value, then?  It was introduced because someone amended 
mouse-yank-primary to call the function called x-get-selection-value if 
it existed (which at the time it only did on w32/dos), then someone else 
decided to fix a bug by reusing the name and call site on x11.

2010-08-14  Eli Zaretskii  <eliz@gnu.org>

	* mouse.el (mouse-yank-primary): Fix mouse-2 on MS-Windows and
	MS-DOS.  (Bug#6689)

bzr diff -r101079..101080

2010-10-31  Jan Djärv  <jan.h.d@swipnet.se>

	* term/x-win.el (x-get-selection-value): New function that gets
	PRIMARY with type as specified in x-select-request-type. (Bug#6802).

  bzr diff -r102166..102167


So x11 x-get-selection-value is a function with the same name as one on 
w32 but very different behaviour, that always returns the primary value 
if available, handling encodings. It is is _not_ X11's 
interprogram-paste function (that's x-selection-value, "obviously"...).
So a fallback to x11 x-get-selection if x11 x-get-selection-value 
returns nothing on x11 is unnecessary but also fairly harmless in 
mouse-yank-primary.


> (I'm asking because my conclusion both from
> reading the X implementation and from your responses, and also from
> discussions archived in bugs #6635 and #6802, is that x-get-selection
> is roughly a limited variant of x-get-selection-value, in that it
> supports less data types.  But I'm probably still missing something.)
>

x-get-selection is the (relatively) lowlevel x11-selection-thingy 
getting function. Bearing in mind that I'm now talking about x11 
selection thingies in general which are used to implement all sorts of 
things, including the x11 clipboard and a bunch of other stuff, not just 
"the" [primary] selection.

i.e. x-get-selection is a more general lower-level x11-selection-thingy 
getting function. x-get-selection-value is a less general higher-level 
function that _only_ gets "the" [primary] selection (on x11! on w32 it's 
a quite different function bound to the same name!), but handling 
certain encoding issues.

You'll find that x11 x-get-selection-value calls x11 
x-selection-value-internal calls x11 x-get-selection.


* removal of the x-get-selection-value call from mouse-yank-primary 
would _now_ break x11, because of later changes mentioned above, but not 
in some hard-to-fix manner.