Getting X selection reliably (Re: idea for capture anywhere in x)

[Max Nikulin <manikulin@gmail.com>]

On 26/10/2022 11:58, Ihor Radchenko wrote:
> 
> Yes. From org-capture-templates docstring:
> 
>    %x          Content of the X clipboard.

Ihor, I am afraid there are a couple of pitfalls with "%x" for Samuel 
since he prefers to keep Emacs hidden so can not check result.

1. If something goes wrong, e.g. some application does not put 
highlighted text to PRIMARY selection then wrong source (CLIPBOARD) or 
empty string may be silently captured. I would prefer explicit source 
however it will not protect against stale selection from the same source.

Simulate empty selection:
echo | xsel -bi ; echo | xsel -i ; killall xsel

2. Jean pointed out that Emacs ignores X selection if it does not have 
an X frame. It was almost buried in the haystack of "SQL instead of Org" 
noise. It happens if Emacs is running as a daemon. I am unsure which way 
Samuel starts Emacs (xinit, systemd user session, systemd socket 
activation, manually, etc.)

What I do not like that error text is captured and no error is returned 
to emacsclient, so checks must be performed in advance.

My suggestion:
~/examples/org/capture-daemon.el
---- >8 ----
(defun nm-check-selection (selection)
   (let ((display (org-string-nw-p (getenv "DISPLAY"))))
     (if display
         (server-select-display display)
       (error "No DISPLAY")))
   (if (org-get-x-clipboard selection)
       t
     (error "No %S selection" selection)))

(custom-set-variables
  '(org-capture-templates
    '(("x" "%x (test)" entry
       (file "/tmp/capture-test.org")
       "* Entry
%U

%x
"
       :immediate-finish t)
      ("p" "primary" entry
       (file "/tmp/capture-test.org")
       "* Primary
%U

%(org-get-x-clipboard 'PRIMARY)
"
        :immediate-finish t))))

(require 'org-capture)
---- 8< ----

emacs -Q -L ~/src/org-mode/lisp/ \
    -L /usr/share/emacs/site-lisp/elpa/htmlize-1.55/ \
    --daemon --load ~/examples/org/capture-daemon.el

emacsclient --eval "(nm-check-selection 'PRIMARY)" \
    --eval '(org-capture nil "p")'

the latter command has non-zero exit code in the case of empty selection.