bug#18371: desktop-read: do not (desktop-clear) when no .emacs.desktop file is found

[Ivan Shmakov]

Package:  emacs
Tags: patch

        As currently implemented, desktop-read calls desktop-clear when
        no .emacs.desktop file is found:

  1114      (if (file-exists-p (desktop-full-file-name))
⋯
  1192        ;; No desktop file found.
  1193        (desktop-clear)
  1194        (let ((default-directory desktop-dirname))
  1195          (run-hooks 'desktop-no-desktop-file-hook))
  1196        (message "No desktop file.")

        While this is likely to be a no-op when desktop-read is called
        from user’s ~/.emacs, – this may actually affect user’s session
        if desktop-read gets called from within an established session.

        And even more so a session containing any “process interaction”
        buffers, – like those one gets with M-x run-scheme or M-x erc.
        (Unless desktop-clear-preserve-buffers is suitably customized
        beforehand, that is.  However, as it seems, that may easily spin
        off the limits of convenience, which may be a bug by itself.)

        Given that desktop-read does /not/ call desktop-clear in the
        “.emacs.desktop is found” branch, and that in that case,
        desktop-read /appends/ to the current session (rather than
        /replacing/ it), I see no good reason to call desktop-clear from
        desktop-read in the other case, either.

        Please thus consider the (trivial) patch MIMEd.

-- 
FSF associate member #7257  http://boycottsystemd.org/  … 3013 B6A0 230E 334A

--- a/lisp/desktop.el
+++ b/lisp/desktop.el
@@ -1190,7 +1190,6 @@
            (desktop-auto-save-enable)
            t))
       ;; No desktop file found.
-      (desktop-clear)
       (let ((default-directory desktop-dirname))
         (run-hooks 'desktop-no-desktop-file-hook))
       (message "No desktop file.")