Add custom desktop minor mode handler for lsp-deferred

Use lsp-deferred instead of lsp-mode even in the case that lsp-mode
appears in the list of minor modes for a file in a user's desktop file
by adding the buffer-local variable lsp--buffer-deferred (which tracks
whether a given buffer was started using lsp-deferred) to the variable
desktop-locals-to-save so that it is persisted in a user's desktop
file, and adding a custom handler to desktop-minor-mode-handlers which
uses this persisted variable to determine whether to use lsp-deferred
of lsp-mode when re-opening a file from the desktop file.

Author: LaurenceWarne

lsp-mode.el

@@ -31,6 +31,7 @@
 (require 'cl-lib)
 (require 'compile)
 (require 'dash)
+(require 'desktop)
 (require 'epg)
 (require 'ewoc)
 (require 'f)
@@ -9124,6 +9125,13 @@ This avoids overloading the server with many files when starting Emacs."
                                      (unless (lsp--init-if-visible)
                                        (add-hook 'window-configuration-change-hook #'lsp--init-if-visible nil t))))))))
 
+(add-to-list 'desktop-locals-to-save 'lsp--buffer-deferred)
+(add-to-list 'desktop-minor-mode-handlers
+             '(lsp-mode . (lambda (desktop-buffer-locals)
+                            (if (alist-get 'lsp--buffer-deferred desktop-buffer-locals)
+                                (lsp-deferred)
+                              (lsp-mode)))))
+
 
 
 (defvar lsp-file-truename-cache (ht))