Subject: Re: bug#31209: 27.0.50; current-kill calls interprogram-paste-function more than once

From: "Basil L. Contovounesios" <[email-masked]>
Date: Wed, 18 Apr 2018 18:52:19 +0100

>From a82c662f645b82f6e9425160b586e8c607dd9a3e Mon Sep 17 00:00:00 2001
From: "Basil L. Contovounesios" <[email-masked]>
Date: Thu, 12 Apr 2018 17:46:37 +0100
Subject: [PATCH 1/2] Do not call interprogram-paste-function repeatedly

* lisp/simple.el (current-kill): Disable interprogram-paste-function
so that kill-new doesn't call it repeatedly when
save-interprogram-paste-before-kill is enabled. (bug#31209)
---
 lisp/simple.el | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/lisp/simple.el b/lisp/simple.el
index b51be3a8f8..15c4a92804 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -4463,7 +4463,10 @@ current-kill
 	  ;; Disable the interprogram cut function when we add the new
 	  ;; text to the kill ring, so Emacs doesn't try to own the
 	  ;; selection, with identical text.
-	  (let ((interprogram-cut-function nil))
+          ;; Also disable the interprogram paste function, so that
+          ;; `kill-new' doesn't call it repeatedly.
+          (let ((interprogram-cut-function nil)
+                (interprogram-paste-function nil))
 	    (if (listp interprogram-paste)
                 ;; Use `reverse' to avoid modifying external data.
                 (mapc #'kill-new (reverse interprogram-paste))
-- 
2.17.0

>From 15d1a619039254df5ba1a43aa97e011bdb40175c Mon Sep 17 00:00:00 2001
From: "Basil L. Contovounesios" <[email-masked]>
Date: Wed, 18 Apr 2018 18:35:38 +0100
Subject: [PATCH 2/2] Improve kill-related documentation (bug#31209)

* doc/lispref/text.texi (Low-Level Kill Ring): Fix typo under
current-kill.  Mention interprogram-paste-function under kill-new
and kill-append.
* lisp/simple.el (save-interprogram-paste-before-kill, kill-new)
(kill-append-merge-undo, kill-append): Touch-up docstrings.
---
 doc/lispref/text.texi | 14 +++++++++-----
 lisp/simple.el        | 31 +++++++++++++++++--------------
 2 files changed, 26 insertions(+), 19 deletions(-)

diff --git a/doc/lispref/text.texi b/doc/lispref/text.texi
index 8cb6cf6242..da09b4ae1c 100644
--- a/doc/lispref/text.texi
+++ b/doc/lispref/text.texi
@@ -1143,7 +1143,7 @@ Low-Level Kill Ring
 @code{current-kill} calls the value of
 @code{interprogram-paste-function} (documented below) before
 consulting the kill ring.  If that value is a function and calling it
-returns a string or a list of several string, @code{current-kill}
+returns a string or a list of several strings, @code{current-kill}
 pushes the strings onto the kill ring and returns the first string.
 It also sets the yanking pointer to point to the kill-ring entry of
 the first string returned by @code{interprogram-paste-function},
@@ -1156,8 +1156,10 @@ Low-Level Kill Ring
 @defun kill-new string &optional replace
 This function pushes the text @var{string} onto the kill ring and
 makes the yanking pointer point to it.  It discards the oldest entry
-if appropriate.  It also invokes the value of
-@code{interprogram-cut-function} (see below).
+if appropriate.  It also invokes the values of
+@code{interprogram-paste-function} (subject to
+the user option @code{save-interprogram-paste-before-kill})
+and @code{interprogram-cut-function} (see below).
 
 If @var{replace} is non-@code{nil}, then @code{kill-new} replaces the
 first element of the kill ring with @var{string}, rather than pushing
@@ -1169,8 +1171,10 @@ Low-Level Kill Ring
 kill ring and makes the yanking pointer point to the combined entry.
 Normally @var{string} goes at the end of the entry, but if
 @var{before-p} is non-@code{nil}, it goes at the beginning.  This
-function also invokes the value of @code{interprogram-cut-function}
-(see below).
+function calls @code{kill-new} as a subroutine, thus causing the
+values of @code{interprogram-cut-function} and possibly
+@code{interprogram-paste-function} (see below) to be invoked by
+extension.
 @end defun
 
 @defvar interprogram-paste-function
diff --git a/lisp/simple.el b/lisp/simple.el
index 15c4a92804..8d04471a63 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -4341,12 +4341,11 @@ kill-ring-yank-pointer
   "The tail of the kill ring whose car is the last thing yanked.")
 
 (defcustom save-interprogram-paste-before-kill nil
-  "Save clipboard strings into kill ring before replacing them.
-When one selects something in another program to paste it into Emacs,
-but kills something in Emacs before actually pasting it,
-this selection is gone unless this variable is non-nil,
-in which case the other program's selection is saved in the `kill-ring'
-before the Emacs kill and one can still paste it using \\[yank] \\[yank-pop]."
+  "Save existing clipboard text into kill ring before replacing it.
+A non-nil value ensures that Emacs kill operations do not
+irrevocably overwrite existing clipboard text by saving it to the
+`kill-ring' prior to the kill.  Such text can subsequently be
+retrieved via \\[yank] \\[yank-pop]]."
   :type 'boolean
   :group 'killing
   :version "23.2")
@@ -4366,7 +4365,7 @@ kill-new
 the front of the kill ring, rather than being added to the list.
 
 When `save-interprogram-paste-before-kill' and `interprogram-paste-function'
-are non-nil, saves the interprogram paste string(s) into `kill-ring' before
+are non-nil, save the interprogram paste string(s) into `kill-ring' before
 STRING.
 
 When the yank handler has a non-nil PARAM element, the original STRING
@@ -4402,20 +4401,24 @@ kill-new
   (if interprogram-cut-function
       (funcall interprogram-cut-function string)))
 
-;; It has been argued that this should work similar to `self-insert-command'
-;; which merges insertions in undo-list in groups of 20 (hard-coded in cmds.c).
+;; It has been argued that this should work like `self-insert-command'
+;; which merges insertions in `buffer-undo-list' in groups of 20
+;; (hard-coded in `undo-auto-amalgamate').
 (defcustom kill-append-merge-undo nil
-  "Whether appending to kill ring also makes \\[undo] restore both pieces of text simultaneously."
+  "Amalgamate appending kills with the last kill for undo.
+When non-nil, appending or prepending text to the last kill makes
+\\[undo] restore both pieces of text simultaneously."
   :type 'boolean
   :group 'killing
   :version "25.1")
 
 (defun kill-append (string before-p)
   "Append STRING to the end of the latest kill in the kill ring.
-If BEFORE-P is non-nil, prepend STRING to the kill.
-Also removes the last undo boundary in the current buffer,
- depending on `kill-append-merge-undo'.
-If `interprogram-cut-function' is set, pass the resulting kill to it."
+If BEFORE-P is non-nil, prepend STRING to the kill instead.
+If `interprogram-cut-function' is non-nil, call it with the
+resulting kill.
+If `kill-append-merge-undo' is non-nil, remove the last undo
+boundary in the current buffer."
   (let* ((cur (car kill-ring)))
     (kill-new (if before-p (concat string cur) (concat cur string))
 	      (or (= (length cur) 0)
-- 
2.17.0

"Basil L. Contovounesios" <[email-masked]> writes:

> Patch addressing this to follow.

I attach two patches.

The first makes current-kill disable interprogram-paste-function in
addition to interprogram-cut-function before calling kill-new.

The second suggests potential clarifications in related documentation,
both in '(elisp) Low-Level Kill Ring' and simple.el docstrings.
Hopefully someone can further improve upon these.

Thanks,

-- 
Basil