Make application configurable in 'with-connection-local-variables'

* doc/lispref/variables.texi (Connection Local Variables):
Explain 'connection-local-default-application'.

* etc/NEWS: Mention 'connection-local-default-application'.

* lisp/files-x.el (connection-local-default-application): New variable.
(connection-local-criteria-for-default-directory): Use it.  (Bug#54405)

* test/lisp/files-x-tests.el
(files-x-test-with-connection-local-variables): Extend test.

4 files changed, 72 insertions, 9 deletions

diff --git a/doc/lispref/variables.texi b/doc/lispref/variables.texi
index d991ae9e277..cd39e6b6470 100644
--- a/doc/lispref/variables.texi
+++ b/doc/lispref/variables.texi
@@ -2418,6 +2418,37 @@ are unwound.  Example:
 @end example
 @end defmac
 
+@defvar connection-local-default-application
+The default application, a symbol, to be applied in
+@code{with-connection-local-variables}.  It defaults to @code{tramp},
+but in case you want to overwrite Tramp's settings temporarily, you
+could let-bind it like
+
+@example
+@group
+(connection-local-set-profile-variables
+  'my-remote-perl
+  '((perl-command-name . "/usr/local/bin/perl5")
+    (perl-command-switch . "-e %s")))
+@end group
+
+@group
+(connection-local-set-profiles
+  '(:application 'my-app :protocol "ssh" :machine "remotehost")
+  'my-remote-perl)
+@end group
+
+@group
+(let ((default-directory "/ssh:remotehost:/working/dir/")
+      (connection-local-default-application 'my-app))
+  (with-connection-local-variables
+    do something useful))
+@end group
+@end example
+
+This variable must not be changed globally.
+@end defvar
+
 @defvar enable-connection-local-variables
 If @code{nil}, connection-local variables are ignored.  This variable
 shall be changed temporarily only in special modes.
diff --git a/etc/NEWS b/etc/NEWS
index e2546bb3ca5..c20d683710d 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -269,12 +269,22 @@ defaults to t, which makes Emacs use the toolkit tooltips.  The
 existing GTK-specific option 'x-gtk-use-system-tooltips' is now an
 alias of this new option.
 
+** Connection-local variables
+
 +++
-** Some connection-local variables are now user options.
+*** Some connection-local variables are now user options.
 The variables 'connection-local-profile-alist' and
 'connection-local-criteria-alist' are now user options, in order to
 make it more convenient to inspect and modify them.
 
++++
+*** The default connection-local application can be changed temporarily.
+Running 'with-connection-local-variables' defaults to application
+'tramp'.  This can be changed by let-binding
+'connection-local-default-application' to another symbol.  This is
+useful when running code in a buffer, where Tramp has already set some
+connection local variables.
+
 ---
 ** New minor mode 'pixel-scroll-precision-mode'.
 When enabled, and if your mouse supports it, you can scroll the
@@ -647,7 +657,7 @@ It narrows to the current node.
 
 +++
 *** 'eudc-expansion-overwrites-query' to 'eudc-expansion-save-query-as-kill'.
-Rename 'eudc-expansion-overwrites-query' to
+'eudc-expansion-overwrites-query' is renamed to
 'eudc-expansion-save-query-as-kill' to reflect the actual behaviour of
 the customization variable.
 
@@ -933,7 +943,7 @@ the thumbnail file.
 ** Dired
 
 *** New user option 'dired-mouse-drag-files'.
-If non-nil, dragging filenames with the mouse in a Dired buffer will
+If non-nil, dragging file names with the mouse in a Dired buffer will
 initiate a drag-and-drop session allowing them to be opened in other
 programs.
 
@@ -1000,7 +1010,7 @@ and friends.
 
 ---
 *** Tramp supports abbreviating remote home directories now.
-When calling 'abbreviate-file-name' on a Tramp filename, the result
+When calling 'abbreviate-file-name' on a Tramp file name, the result
 will abbreviate the user's home directory, for example by abbreviating
 "/ssh:user@host:/home/user" to "/ssh:user@host:~".
 
diff --git a/lisp/files-x.el b/lisp/files-x.el
index 319bfe05655..0ae9fb076eb 100644
--- a/lisp/files-x.el
+++ b/lisp/files-x.el
@@ -722,14 +722,18 @@ will not be changed."
         (copy-tree connection-local-variables-alist)))
    (hack-local-variables-apply)))
 
+(defvar connection-local-default-application 'tramp
+  "Default application in connection-local functions, a symbol.
+This variable must not be changed globally.")
+
 (defsubst connection-local-criteria-for-default-directory (&optional application)
   "Return a connection-local criteria, which represents `default-directory'.
-If APPLICATION is nil, the symbol `tramp' is used."
+If APPLICATION is nil, `connection-local-default-application' is used."
   (when (file-remote-p default-directory)
-    `(:application ,(or application 'tramp)
-       :protocol   ,(file-remote-p default-directory 'method)
-       :user       ,(file-remote-p default-directory 'user)
-       :machine    ,(file-remote-p default-directory 'host))))
+    `(:application ,(or application connection-local-default-application)
+      :protocol    ,(file-remote-p default-directory 'method)
+      :user        ,(file-remote-p default-directory 'user)
+      :machine     ,(file-remote-p default-directory 'host))))
 
 ;;;###autoload
 (defmacro with-connection-local-variables (&rest body)
diff --git a/test/lisp/files-x-tests.el b/test/lisp/files-x-tests.el
index 60787e1cd3d..7ee2f0c1a65 100644
--- a/test/lisp/files-x-tests.el
+++ b/test/lisp/files-x-tests.el
@@ -325,6 +325,9 @@
         (should-not (boundp 'remote-shell-file-name))
         (should (string-equal (symbol-value 'remote-null-device) "null"))
 
+        (connection-local-set-profiles
+         files-x-test--application 'remote-bash)
+
 	(with-connection-local-variables
 	 ;; All connection-local variables are set.  They apply in
 	 ;; reverse order in `connection-local-variables-alist'.
@@ -347,6 +350,21 @@
          (should
           (string-equal (symbol-value 'remote-shell-file-name) "/bin/ksh"))
          (should
+          (string-equal (symbol-value 'remote-null-device) "/dev/null"))
+
+         ;; Run another instance of `with-connection-local-variables'
+         ;; with a different application.
+         (let ((connection-local-default-application (cadr files-x-test--application)))
+	   (with-connection-local-variables
+            ;; The proper variable values are set.
+            (should
+             (string-equal (symbol-value 'remote-shell-file-name) "/bin/bash"))
+            (should
+             (string-equal (symbol-value 'remote-null-device) "/dev/null"))))
+         ;; The variable values are reset.
+         (should
+          (string-equal (symbol-value 'remote-shell-file-name) "/bin/ksh"))
+         (should
           (string-equal (symbol-value 'remote-null-device) "/dev/null")))
 
 	;; Everything is rewound.  The old variable values are reset.