bug#53894: 27.2; Clipboard copy -> C-y -> M-y -> Same clipboard copy does not push to kill ring

[Ignacio Casso]

>> I volunteer to do both if you agree that it would be an improvement.
>
> I do agree, any patches would be greatly welcome.  Thanks in advance.

I have installed the development version of Emacs and made a first patch
attempt, preserving the structure of the program as much as possible. I
have not tested thoroughly, but it works for all the cases I have
tried. I have attached it to this mail, and comment each change
below. Let me know what you think.

>  lisp/menu-bar.el           |  4 +--
>  lisp/obsolete/mouse-sel.el |  2 +-
>  lisp/select.el             | 70 +++++++++++++++++++++++---------------
>  lisp/term/pc-win.el        |  2 +-
>  5 files changed, 47 insertions(+), 33 deletions(-)
> 
> diff --git a/lisp/menu-bar.el b/lisp/menu-bar.el
> index ab64928fe7..01683f5c9f 100644
> --- a/lisp/menu-bar.el
> +++ b/lisp/menu-bar.el
> @@ -606,8 +606,8 @@ clipboard-yank
>    "Insert the clipboard contents, or the last stretch of killed text."
>    (interactive "*")
>    (let ((select-enable-clipboard t)
> -        ;; Ensure that we defeat the DWIM login in `gui-selection-value'.
> -        (gui--last-selected-text-clipboard nil))
> +        ;; Ensure that we defeat the DWIM logic in `gui-selection-value'.
> +        (gui--last-clipboard-selection-fingerprint nil))
>      (yank)))
>  
>  (defun clipboard-kill-ring-save (beg end &optional region)

- DWIM login -> DWIM logic (typo)

- replaced gui--last-selected-text-clipboard variable with the new one I
  have introduced (explained below)

- I have tested that clipboard-yank works for the following cases:
  - (setq select-enable-clipboard nil) -> copy in another program -> 
clipboard-yank
  another program.
  - copy in another program -> C-y -> M-y -> clipboard-yank

> diff --git a/lisp/obsolete/mouse-sel.el b/lisp/obsolete/mouse-sel.el
> index a9d6bfee60..fc91cc9fc1 100644
> --- a/lisp/obsolete/mouse-sel.el
> +++ b/lisp/obsolete/mouse-sel.el
> @@ -304,7 +304,7 @@ mouse-sel-get-selection-function
>      (if (eq selection 'PRIMARY)
>       (or (gui-selection-value)
>           (bound-and-true-p x-last-selected-text-primary)
> -            gui--last-selected-text-primary)
> +            gui--last-selected-text-primary) ;; this variable no longer 
> exists. Does code in lisp/obsolete/ need to be mantained?
>        (gui-get-selection selection)))
>    "Function to call to get the selection.
>  Called with one argument:

Here I have not replaced the variable, since I have assumed that code
under the obsolete/ directory does not need to be maintained, and C-h f
tells me that function is not loaded by default. However there is a
warning when compiling. Should I fix it?


> diff --git a/lisp/select.el b/lisp/select.el
> index 42b50c44e6..55c409d347 100644
> --- a/lisp/select.el
> +++ b/lisp/select.el
> @@ -25,9 +25,10 @@
>  ;; Based partially on earlier release by Lucid.
>  
>  ;; The functionality here is divided in two parts:
> -;; - Low-level: gui-get-selection, gui-set-selection, gui-selection-owner-p,
> -;;   gui-selection-exists-p are the backend-dependent functions meant to 
> access
> -;;   various kinds of selections (CLIPBOARD, PRIMARY, SECONDARY).
> +;; - Low-level: gui-backend-get-selection, gui-backend-set-selection,
> +;;   gui-backend-selection-owner-p, gui-backend-selection-exists-p are
> +;;   the backend-dependent functions meant to access various kinds of
> +;;   selections (CLIPBOARD, PRIMARY, SECONDARY).
>  ;; - Higher-level: gui-select-text and gui-selection-value go together to
>  ;;   access the general notion of "GUI selection" for interoperation with 
> other
>  ;;   applications.  This can use either the clipboard or the primary 
> selection,

- gui-selection-owner-p -> gui-backend-selection-owner-p (the former does
not exist)

- gui-selection-exists-p -> gui-backend-selection-exists-p (the
  former does not exist)

- gui-get-selection -> gui-backend-get-selection (the former
  does exist, but the later is lower lever, and I assumed that if the
  previous needed to be updated this one probably too)

- gui-set-selection -> gui-backend-set-selection (same as above)

> @@ -108,16 +109,24 @@ select-enable-primary
>    :group 'killing
>    :version "25.1")
>  
> -;; We keep track of the last text selected here, so we can check the
> -;; current selection against it, and avoid passing back our own text
> -;; from gui-selection-value.  We track both
> +;; We keep track of the last selection here, so we can check the
> +;; current selection against it, and avoid passing back with
> +;; gui-selection-value the same text we previously killed or
> +;; yanked. We track both
>  ;; separately in case another X application only sets one of them
>  ;; we aren't fooled by the PRIMARY or CLIPBOARD selection staying the same.
> +;;
> +;; TODO: add selection owner to fingerprint, since timestamp is not
> +;; always relieable? Probably not worth it, since right now we can't
> +;; get the owner with the low-level functions out of the box, and text
> +;; plus timestamp is probably a strong enough fingerprint already.
> +(defvar gui--last-clipboard-selection-fingerprint nil
> +  "The fingerprint of the CLIPBOARD selection last seen, which is a
> +list of value and timestamp.")
> +(defvar gui--last-primary-selection-fingerprint nil
> +  "The fingerprint of the PRIMARY selection last seen, which is a
> +list of value and timestamp.")
>  
> -(defvar gui--last-selected-text-clipboard nil
> -  "The value of the CLIPBOARD selection last seen.")
> -(defvar gui--last-selected-text-primary nil
> -  "The value of the PRIMARY selection last seen.")
>  
>  (defun gui-select-text (text)
>    "Select TEXT, a string, according to the window system.

- Using new variables gui--last-clipboard-selection-fingerprint and
  gui--last-primary-selection-fingerprint instead of
  gui--last-selected-text-clipboard and
  gui--last-selected-text-primary. They have the same purpose but hold
  the text and the timestamp instead of just the text, and I have
  updated the code everywhere they were referenced to use the
  text-timestamp pair instead of just the text . Better ideas for the
  names are welcome.

- Updated previous comment

- Just threw the idea that a better fingerprint would include the owner
  of the selection, if timestamps are sometimes not updated precisely
  when the owner changes, as Po Lu said.


> @@ -127,14 +136,16 @@ gui-select-text
>  MS-Windows does not have a \"primary\" selection."
>    (when select-enable-primary
>      (gui-set-selection 'PRIMARY text)
> -    (setq gui--last-selected-text-primary text))
> +    (setq gui--last-primary-selection-fingerprint
> +          (list text (gui-get-selection 'PRIMARY 'TIMESTAMP))))
>    (when select-enable-clipboard
>      ;; When cutting, the selection is cleared and PRIMARY
>      ;; set to the empty string.  Prevent that, PRIMARY
>      ;; should not be reset by cut (Bug#16382).
>      (setq saved-region-selection text)
>      (gui-set-selection 'CLIPBOARD text)
> -    (setq gui--last-selected-text-clipboard text)))
> +    (setq gui--last-clipboard-selection-fingerprint
> +          (list text (gui-get-selection 'CLIPBOARD 'TIMESTAMP)))))
>  (define-obsolete-function-alias 'x-select-text 'gui-select-text "25.1")
>  
>  (defcustom x-select-request-type nil

Saving the text-timestamp pair instead of just text.

> @@ -175,6 +186,7 @@ gui--selection-value-internal
>             ;; some other window systems.
>             (memq window-system '(x haiku))
>             (eq type 'CLIPBOARD)
> +           ;; Should we unify this with the DWIM logic?
>             (gui-backend-selection-owner-p type))
>      (let ((request-type (if (memq window-system '(x pgtk haiku))
>                              (or x-select-request-type

I consider that check to be conceptually part of the same DWIM logic,
and feel that maybe both checks should go together in the code. However
I decided to preserve the code structure for now, since I wanted to make
as little changes as possible, having the ownership check there can save
unnecessary computations, and the check is mostly redundant now
otherwise.


> @@ -194,33 +206,34 @@ gui--selection-value-internal
>  (defun gui-selection-value ()
>    (let ((clip-text
>           (when select-enable-clipboard
> -           (let ((text (gui--selection-value-internal 'CLIPBOARD)))
> +           (let ((text (gui--selection-value-internal 'CLIPBOARD))
> +                 (timestamp (gui-get-selection 'CLIPBOARD 'TIMESTAMP)))
>               (when (string= text "")
>                 (setq text nil))
> -             ;; When `select-enable-clipboard' is non-nil,
> -             ;; killing/copying text (with, say, `C-w') will push the
> -             ;; text to the clipboard (and store it in
> -             ;; `gui--last-selected-text-clipboard').  We check
> -             ;; whether the text on the clipboard is identical to this
> -             ;; text, and if so, we report that the clipboard is
> -             ;; empty.  See (bug#27442) for further discussion about
> -             ;; this DWIM action, and possible ways to make this check
> -             ;; less fragile, if so desired.
> +             ;; Check the CLIPBOARD selection for 'newness', i.e.,
> +             ;; whether it is different from the last time we did a
> +             ;; yank operation or whether it was set by Emacs itself
> +             ;; with a kill operation, since in both cases the text
> +             ;; will already be in the kill ring. See (bug#27442) and
> +             ;; (bug#53894) for further discussion about this DWIM
> +             ;; action, and possible ways to make this check less
> +             ;; fragile, if so desired.
>               (prog1
> -                 (unless (equal text gui--last-selected-text-clipboard)
> +                 (unless (equal (list text timestamp)  
> gui--last-clipboard-selection-fingerprint)
>                     text)
> -               (setq gui--last-selected-text-clipboard text)))))
> +               (setq gui--last-clipboard-selection-fingerprint (list text 
> timestamp))))))
>          (primary-text
>           (when select-enable-primary
> -           (let ((text (gui--selection-value-internal 'PRIMARY)))
> +           (let ((text (gui--selection-value-internal 'PRIMARY))
> +                 (timestamp (gui-get-selection 'PRIMARY 'TIMESTAMP)))
>               (if (string= text "") (setq text nil))
>               ;; Check the PRIMARY selection for 'newness', is it different
>               ;; from what we remembered them to be last time we did a
>               ;; cut/paste operation.
>               (prog1
> -                 (unless (equal text gui--last-selected-text-primary)
> +                 (unless (equal (list text timestamp)  
> gui--last-primary-selection-fingerprint)
>                     text)
> -               (setq gui--last-selected-text-primary text))))))
> +               (setq gui--last-primary-selection-fingerprint (list text 
> timestamp)))))))
>  
>      ;; As we have done one selection, clear this now.
>      (setq next-selection-coding-system nil)

- Using the timestamp-text pair instead of just text

- Updated comments

- I have tested the following cases:

  - Copy in another program -> C-y

  - Copy in other program -> C-y -> C-y -> M-y (the copied text is not
    duplicated in the kill ring, i.e., gui-selection-value returns nil
    for the second C-y)

  - C-k -> C-y -> M-y (the killed text is not duplicated in the kill
    ring, i.e., gui-selection-value returns nil)

  - Copy something in other program -> C-y -> M-y -> Copy the same thing
    in other program -> C-y (works as expected, i.e., the bug I reported
    is fixed)


> @@ -239,7 +252,8 @@ gui-selection-value
>      ;; timestamps there is no way to know what the 'correct' value to
>      ;; return is.  The nice thing to do would be to tell the user we
>      ;; saw multiple possible selections and ask the user which was the
> -    ;; one they wanted.
> +    ;; one they wanted. EDIT: We do have timestamps now, so we can
> +    ;; return the newer.
>      (or clip-text primary-text)
>      ))
>  

An unrelated issue which could be solved with timestamps, but the comment
must be old and says we don't have them. Just updated the comment saying
we do have them now.

> diff --git a/lisp/term/pc-win.el b/lisp/term/pc-win.el
> index 327d51f275..2ae3cbd8b2 100644
> --- a/lisp/term/pc-win.el
> +++ b/lisp/term/pc-win.el
> @@ -248,7 +248,7 @@ w16-selection-owner-p
>          ;; Windows clipboard.
>          (cond
>           ((not text) t)
> -         ((equal text gui--last-selected-text-clipboard) text)
> +         ((equal text (car gui--last-clipbaord-selection-fingerprint)) t)
>           (t nil)))))
>  

- Replaced the check

- Returned t instead of text

- Have not tested since I don't use Windows, but it's semantically
  equivalent as before.

0001-fixed-bug.patch
Description: Patch for bug#53894