Add helpers to dynamically assign connection-local values

* lisp/files-x.el (connection-local-criteria)
(connection-local-profile-name-for-setq): New variables.
(with-connection-local-variables-1): ... let-bind them here.
(connection-local-update-profile-variables)
(connection-local-profile-name-for-criteria): New functions.
(with-connection-local-application-variables, setq-connection-local):
New macros.

* test/lisp/files-x-tests.el: Require 'tramp-integration'
(files-x-test--variable5, remote-lazy-var): New variables.
(files-x-test-hack-connection-local-variables-apply): Expand checks.
(files-x-test-with-connection-local-variables): Remove
'hack-connection-local-variables-apply' check (it belongs in the above
test), and expand some other checks.
(files-x-test--get-lazy-var, files-x-test--set-lazy-var): New
functions.
(files-x-test-connection-local-update-profile-variables)
(files-x-test-setq-connection-local): New tests.

* doc/lispref/variables.texi (Connection Local Variables): Split into
two subsections and document the new features.

* etc/NEWS: Announce 'setq-connection-local'.

1 files changed, 98 insertions, 5 deletions

diff --git a/lisp/files-x.el b/lisp/files-x.el
index 0131d495f27..3516592fc3e 100644
--- a/lisp/files-x.el
+++ b/lisp/files-x.el
@@ -620,6 +620,18 @@ PROFILES is a list of connection profiles (symbols)."
   :group 'tramp
   :version "29.1")
 
+(defvar connection-local-criteria nil
+  "The current connection-local criteria, or nil.
+This is set while executing the body of
+`with-connection-local-variables'.")
+
+(defvar connection-local-profile-name-for-setq nil
+  "The current connection-local profile name, or nil.
+This is the name of the profile to use when setting variables via
+`setq-connection-local'.  Its value is derived from
+`connection-local-criteria' and is set while executing the body
+of `with-connection-local-variables'.")
+
 (defsubst connection-local-normalize-criteria (criteria)
   "Normalize plist CRITERIA according to properties.
 Return a reordered plist."
@@ -696,6 +708,23 @@ in order."
   (customize-set-variable
    'connection-local-profile-alist connection-local-profile-alist))
 
+;;;###autoload
+(defun connection-local-update-profile-variables (profile variables)
+  "Update the variable settings for PROFILE in-place.
+VARIABLES is a list that declares connection-local variables for
+the connection profile.  An element in VARIABLES is an alist
+whose elements are of the form (VAR . VALUE).
+
+Unlike `connection-local-set-profile-variables' (which see), this
+function preserves the values of any existing variable
+definitions that aren't listed in VARIABLES."
+  (when-let ((existing-variables
+              (nreverse (connection-local-get-profile-variables profile))))
+    (dolist (var variables)
+      (setf (alist-get (car var) existing-variables) (cdr var)))
+    (setq variables (nreverse existing-variables)))
+  (connection-local-set-profile-variables profile variables))
+
 (defun hack-connection-local-variables (criteria)
   "Read connection-local variables according to CRITERIA.
 Store the connection-local variables in buffer local
@@ -738,6 +767,15 @@ If APPLICATION is nil, `connection-local-default-application' is used."
       :user        ,(file-remote-p default-directory 'user)
       :machine     ,(file-remote-p default-directory 'host))))
 
+(defun connection-local-profile-name-for-criteria (criteria)
+  "Get a connection-local profile name based on CRITERIA."
+  (when criteria
+    (let (print-level print-length)
+      (intern (concat
+               "autogenerated-connection-local-profile/"
+               (prin1-to-string
+                (connection-local-normalize-criteria criteria)))))))
+
 ;;;###autoload
 (defmacro with-connection-local-variables (&rest body)
   "Apply connection-local variables according to `default-directory'.
@@ -746,15 +784,27 @@ Execute BODY, and unwind connection-local variables."
   `(with-connection-local-variables-1 (lambda () ,@body)))
 
 ;;;###autoload
+(defmacro with-connection-local-application-variables (application &rest body)
+  "Apply connection-local variables for APPLICATION in `default-directory'.
+Execute BODY, and unwind connection-local variables."
+  (declare (debug t) (indent 1))
+  `(let ((connection-local-default-application ,application))
+     (with-connection-local-variables-1 (lambda () ,@body))))
+
+;;;###autoload
 (defun with-connection-local-variables-1 (body-fun)
   "Apply connection-local variables according to `default-directory'.
 Call BODY-FUN with no args, and then unwind connection-local variables."
   (if (file-remote-p default-directory)
-      (let ((enable-connection-local-variables t)
-            (old-buffer-local-variables (buffer-local-variables))
-	    connection-local-variables-alist)
-	(hack-connection-local-variables-apply
-	 (connection-local-criteria-for-default-directory))
+      (let* ((enable-connection-local-variables t)
+             (connection-local-criteria
+              (connection-local-criteria-for-default-directory))
+             (connection-local-profile-name-for-setq
+              (connection-local-profile-name-for-criteria
+               connection-local-criteria))
+             (old-buffer-local-variables (buffer-local-variables))
+	     connection-local-variables-alist)
+	(hack-connection-local-variables-apply connection-local-criteria)
 	(unwind-protect
             (funcall body-fun)
 	  ;; Cleanup.
@@ -767,6 +817,49 @@ Call BODY-FUN with no args, and then unwind connection-local variables."
     (funcall body-fun)))
 
 ;;;###autoload
+(defmacro setq-connection-local (&rest pairs)
+  "Set each VARIABLE connection-locally to VALUE.
+
+When `connection-local-profile-name-for-setq' is set, assign each
+variable's value on that connection profile, and set that profile
+for `connection-local-criteria'.  You can use this in combination
+with `with-connection-local-variables', as in
+
+  (with-connection-local-variables
+    (setq-connection-local VARIABLE VALUE))
+
+If there's no connection-local profile to use, just set the
+variables normally, as with `setq'.
+
+The variables are literal symbols and should not be quoted.  The
+second VALUE is not computed until after the first VARIABLE is
+set, and so on; each VALUE can use the new value of variables set
+earlier in the `setq-connection-local'.  The return value of the
+`setq-connection-local' form is the value of the last VALUE.
+
+\(fn [VARIABLE VALUE]...)"
+  (declare (debug setq))
+  (unless (zerop (mod (length pairs) 2))
+    (error "PAIRS must have an even number of variable/value members"))
+  (let ((set-expr nil)
+        (profile-vars nil))
+    (while pairs
+      (unless (symbolp (car pairs))
+        (error "Attempting to set a non-symbol: %s" (car pairs)))
+      (push `(set ',(car pairs) ,(cadr pairs)) set-expr)
+      (push `(cons ',(car pairs) ,(car pairs)) profile-vars)
+      (setq pairs (cddr pairs)))
+    `(prog1
+         ,(macroexp-progn (nreverse set-expr))
+       (when connection-local-profile-name-for-setq
+         (connection-local-update-profile-variables
+          connection-local-profile-name-for-setq
+          (list ,@(nreverse profile-vars)))
+         (connection-local-set-profiles
+          connection-local-criteria
+          connection-local-profile-name-for-setq)))))
+
+;;;###autoload
 (defun path-separator ()
   "The connection-local value of `path-separator'."
   (with-connection-local-variables path-separator))