bug#70959: Tramp connection property can interact weirdly with cache

[Dmitry Gutov <dmitry@gutov.dev>]

Hi Michael,

On 18/05/2024 21:43, Michael Albinus wrote:
> Try the following patch and the config as shown above.
> 
> 
> diff --git a/lisp/tramp.el b/lisp/tramp.el
> index f024ebec..814d33e6 100644
> --- a/lisp/tramp.el
> +++ b/lisp/tramp.el
> @@ -4847,6 +4847,8 @@ a connection-local variable."
>     (when (process-command proc)
>       (tramp-message vec 6 "%s" (string-join (process-command proc) " "))))
> 
> +(defvar tramp-direct-async-process nil)
> +
>   (defun tramp-direct-async-process-p (&rest args)
>     "Whether direct async `make-process' can be called."
>     (let ((v (tramp-dissect-file-name default-directory))
> @@ -4855,7 +4857,7 @@ a connection-local variable."
>       (and ;; The method supports it.
>            (tramp-get-method-parameter v 'tramp-direct-async)
>   	 ;; It has been indicated.
> -         (tramp-get-connection-property v "direct-async-process")
> +	 (connection-local-value tramp-direct-async-process)

Do you think we could also make it so

  (setq tramp-direct-async-process t)

in the user config also works? Affecting all connections, naturally.

Not sure if we'll want to advertise it as a proper way to apply this 
config, but I'd probably use this shortcut myself, and especially during 
testing.

E.g. the change below (or equivalent):

diff --git a/lisp/net/tramp.el b/lisp/net/tramp.el
index 18116229337..1864ef6541d 100644
--- a/lisp/net/tramp.el
+++ b/lisp/net/tramp.el
@@ -4878,9 +4878,7 @@ tramp-direct-async-process-p
           (tramp-get-method-parameter v 'tramp-direct-async)
  	 ;; It has been indicated.  We don't use the global value of
  	 ;; `tramp-direct-async-process'.
-	 (or (and (tramp-compat-connection-local-p tramp-direct-async-process)
-		  (tramp-compat-connection-local-value
-		   tramp-direct-async-process))
+	 (or (with-connection-local-variables tramp-direct-async-process)
  	     ;; Deprecated setting.
               (tramp-get-connection-property v "direct-async-process"))
  	 ;; There's no multi-hop.