Subject: bug#58608: 29.0.50; Nasty bug with pasting primary selection in term buffers

From: Phil Sainty <[email-masked]>
Date: Wed, 19 Oct 2022 13:53:09 +1300

The `deactivate-mark' call in `term-send-raw-string' is the direct
cause of the unwanted change to the selection.  In more detail...

In line mode middle click calls `mouse-yank-primary', but in char mode
middle click calls:

(defun term-mouse-paste (click)
   "Insert the primary selection at the position clicked on."
   (interactive "e")
   ;; Give temporary modes such as isearch a chance to turn off.
   (run-hooks 'mouse-leave-buffer-hook)
   (setq this-command 'yank)
   (mouse-set-point click)
   (term-send-raw-string (gui-get-primary-selection)))

I traced the following:

(trace-function 'mouse-set-point nil
		(lambda () (format " [%s]" (gui-get-primary-selection))))

(trace-function 'term-mouse-paste nil
		(lambda () (format " [%s]" (gui-get-primary-selection))))

(trace-function 'gui-get-primary-selection)

(trace-function 'term-send-raw-string)

Notice that I'm triggering `gui-get-primary-selection' more often
than it would otherwise be called, by also calling it for context.

My terminal buffer contained the line "this is a test" and I selected
"this" with the mouse, and then middle clicked after the word "test".

We see `term-mouse-paste' passing `term-send-raw-string' the word
"this" after obtaining it from `gui-get-primary-selection'; but then,
after the return of `term-send-raw-string' but *before* the return of
`term-mouse-paste', my call-for-context to `gui-get-primary-selection'
fires, returning the longer string "this is a test".

======================================================================
1 -> (term-mouse-paste (mouse-2 (#<window 8 on *terminal*> 457 (191 . 
226) 421854684 nil 457 (21 . 12) nil (65 . 10) (9 . 18)))) [this]
| 2 -> (gui-get-primary-selection)
| 2 <- gui-get-primary-selection: #("this" 0 1 (font-lock-face term 
fontified t) 1 2 (font-lock-face term fontified t) 2 3 (font-lock-face 
term fontified t) 3 4 (font-lock-face term fontified t))
| 2 -> (mouse-set-point (mouse-2 (#<window 8 on *terminal*> 457 (191 . 
226) 421854684 nil 457 (21 . 12) nil (65 . 10) (9 . 18)))) [this]
| | 3 -> (gui-get-primary-selection)
| | 3 <- gui-get-primary-selection: #("this" 0 1 (font-lock-face term 
fontified t) 1 2 (font-lock-face term fontified t) 2 3 (font-lock-face 
term fontified t) 3 4 (font-lock-face term fontified t))
| 2 <- mouse-set-point: 457 [this]
| 2 -> (gui-get-primary-selection)
| 2 <- gui-get-primary-selection: #("this" 0 1 (font-lock-face term 
fontified t) 1 2 (font-lock-face term fontified t) 2 3 (font-lock-face 
term fontified t) 3 4 (font-lock-face term fontified t))
| 2 -> (term-send-raw-string #("this" 0 1 (font-lock-face term fontified 
t) 1 2 (font-lock-face term fontified t) 2 3 (font-lock-face term 
fontified t) 3 4 (font-lock-face term fontified t)))
| 2 <- term-send-raw-string: nil
| 2 -> (gui-get-primary-selection)
| 2 <- gui-get-primary-selection: #("this is a test" 0 1 (font-lock-face 
term fontified t) 1 2 (font-lock-face term fontified t) 2 3 
(font-lock-face term fontified t) 3 4 (font-lock-face term fontified t) 
4 5 (font-lock-face term fontified t) 5 6 (font-lock-face term fontified 
t) 6 7 (font-lock-face term fontified t) 7 8 (font-lock-face term 
fontified t) 8 9 (font-lock-face term fontified t) 9 10 (font-lock-face 
term fontified t) 10 11 (font-lock-face term fontified t) 11 12 
(font-lock-face term fontified t) 12 13 (font-lock-face term fontified 
t) 13 14 (font-lock-face term fontified t))
1 <- term-mouse-paste: nil [this is a test]
======================================================================

So immediately after (term-send-raw-string (gui-get-primary-selection))
has inserted "this" a second (gui-get-primary-selection) is returning
"this is a test"; so `term-send-raw-string' itself seems like a factor.

I then added some messaging like so:

(defun term-mouse-paste (click)
   "Insert the primary selection at the position clicked on."
   (interactive "e")
   ;; Give temporary modes such as isearch a chance to turn off.
   (run-hooks 'mouse-leave-buffer-hook)
   (setq this-command 'yank)
   (mouse-set-point click)
   (message "before: %s" (gui-get-primary-selection))
   (term-send-raw-string (gui-get-primary-selection))
   (message "after: %s" (gui-get-primary-selection)))

(defun term-send-raw-string (chars)
   (message "0: %s" (gui-get-primary-selection))
   (deactivate-mark)
   (message "1: %s" (gui-get-primary-selection))
   ...)

Which gave me these *Messages*:

before: this
0: this
1: this is a test
after: this is a test

So the `deactivate-mark' call in `term-send-raw-string' causes the
unwanted change to the selection.

-Phil