Add option 'ffap-prefer-remote-file' (bug#78925)

This option only affects absolute filenames that are found by
ffap-file-at-point in buffers with remote default directory.

The handling of relative filenames in above buffers remains
unchanged: ffap-file-at-point returns the relative filename,
which can be converted to a remote absolute filename by
subsequent callers (e.g. ffap) using expand-file-name.

* lisp/ffap.el (ffap-prefer-remote-file): New user option.
(ffap-file-exists-string): Add an optional argument to allow the
check of existence of absolute filename on the remote host.
(ffap-file-at-point): Always find remote files in remote context
if the new option is non-nil.
* test/lisp/ffap-tests.el (ffap-test-remote): Add a test.
* etc/NEWS: Announce the change.

3 files changed, 77 insertions, 25 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 5457ed3c4d4..b3c2287589a 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -2249,6 +2249,12 @@ useful when you want the face attributes to be absolute and not
 'unspecified'.
 
 ---
+*** New user option 'ffap-prefer-remote-file'.
+If non-nil, ffap always finds remote files in buffers with remote
+'default-directory'.  If nil, ffap finds local files first for absolute
+filenames in above buffers.  The default is nil.
+
+---
 ** Flymake
 
 *** Windows without fringes now automatically use margin indicators.
diff --git a/lisp/ffap.el b/lisp/ffap.el
index 10afcd9514a..64c2c780672 100644
--- a/lisp/ffap.el
+++ b/lisp/ffap.el
@@ -199,6 +199,16 @@ Sensible values are nil, \"news\", or \"mailto\"."
                  )
   :group 'ffap)
 
+(defcustom ffap-prefer-remote-file nil
+  "Whether to prefer remote files in remote context.
+If non-nil, ffap always finds remote files in buffers with remote
+`default-directory'.  If nil, ffap finds local files first for absolute
+filenames in above buffers.  Relative filenames are not affected by this
+option."
+  :type 'boolean
+  :group 'ffap
+  :version "31.1")
+
 (defvar ffap-max-region-length 1024
   "Maximum active region length.
 When the region is active and larger than this value,
@@ -488,7 +498,7 @@ Returned values:
 (defvar ffap-compression-suffixes '(".gz" ".Z") ; .z is mostly dead
   "List of suffixes tried by `ffap-file-exists-string'.")
 
-(defun ffap-file-exists-string (file &optional nomodify)
+(defun ffap-file-exists-string (file &optional nomodify remote-host)
   ;; Early jka-compr versions modified file-exists-p to return the
   ;; filename, maybe modified by adding a suffix like ".gz".  That
   ;; broke the interface of file-exists-p, so it was later dropped.
@@ -496,23 +506,33 @@ Returned values:
   "Return FILE (maybe modified) if the file exists, else nil.
 When using jka-compr (a.k.a. `auto-compression-mode'), the returned
 name may have a suffix added from `ffap-compression-suffixes'.
-The optional NOMODIFY argument suppresses the extra search."
-  (cond
-   ((or (not file)                      ; quietly reject nil
-        (zerop (length file)))          ; and also ""
-    nil)
-   ((file-exists-p file) file)          ; try unmodified first
-   ;; three reasons to suppress search:
-   (nomodify nil)
-   ((not (rassq 'jka-compr-handler file-name-handler-alist)) nil)
-   ((member (file-name-extension file t) ffap-compression-suffixes) nil)
-   (t                                   ; ok, do the search
-    (let ((list ffap-compression-suffixes) try ret)
-      (while list
-        (if (file-exists-p (setq try (concat file (car list))))
-            (setq ret try list nil)
-          (setq list (cdr list))))
-      ret))))
+The optional NOMODIFY argument suppresses the extra search.
+
+The optional argument REMOTE-HOST, if non-nil, should be a string
+returned by `file-remote-p'.  If it is non-nil and FILE is absolute,
+check whether FILE exists on REMOTE-HOST.  The returned name uses
+REMOTE-HOST as the prefix if the file exists."
+  (let ((non-essential t))
+    (cond
+     ((or (not file)                    ; quietly reject nil
+          (zerop (length file)))        ; and also ""
+      nil)
+     ((and remote-host                  ; prepend remote host to file
+           (file-name-absolute-p file)
+           (setq file (concat remote-host file))
+           nil))
+     ((file-exists-p file) file)
+     ;; three reasons to suppress search:
+     (nomodify nil)
+     ((not (rassq 'jka-compr-handler file-name-handler-alist)) nil)
+     ((member (file-name-extension file t) ffap-compression-suffixes) nil)
+     (t                                 ; ok, do the search
+      (let ((list ffap-compression-suffixes) try ret)
+        (while list
+          (if (file-exists-p (setq try (concat file (car list))))
+              (setq ret try list nil)
+            (setq list (cdr list))))
+        ret)))))
 
 (defun ffap-file-remote-p (filename)
   "If FILENAME looks remote, return it (maybe slightly improved)."
@@ -1465,6 +1485,8 @@ which may actually result in an URL rather than a filename."
               string))
          (abs (file-name-absolute-p name))
          (default-directory default-directory)
+         (remote-p (and ffap-prefer-remote-file
+                        (file-remote-p default-directory)))
          (oname name))
     (unwind-protect
         (cond
@@ -1484,10 +1506,11 @@ which may actually result in an URL rather than a filename."
          ;; Accept remote names without actual checking (too slow):
          ((and abs (ffap-file-remote-p name)))
          ;; Ok, not remote, try the existence test even if it is absolute:
-         ((and abs (ffap-file-exists-string name)))
+         ((and abs (ffap-file-exists-string name nil remote-p)))
          ;; Try stripping off line numbers.
          ((and abs (string-match ":[0-9]" name)
-               (ffap-file-exists-string (substring name 0 (match-beginning 0)))))
+               (ffap-file-exists-string (substring name 0 (match-beginning 0))
+                                        nil remote-p)))
          ;; If it contains a colon, get rid of it (and return if exists)
          ((and (string-match path-separator name)
                (let ((this-name (ffap-string-at-point 'nocolon)))
@@ -1495,7 +1518,7 @@ which may actually result in an URL rather than a filename."
                  ;; the empty string.
                  (when (> (length this-name) 0)
                    (setq name this-name)
-                   (ffap-file-exists-string name)))))
+                   (ffap-file-exists-string name nil remote-p)))))
          ;; File does not exist, try the alist:
          ((let ((alist ffap-alist) tem try case-fold-search)
             (while (and alist (not try))
@@ -1510,7 +1533,7 @@ which may actually result in an URL rather than a filename."
                        (setq try (or
                                   (ffap-url-p try) ; not a file!
                                   (ffap-file-remote-p try)
-                                  (ffap-file-exists-string try))))))
+                                  (ffap-file-exists-string try nil remote-p))))))
             try))
          ;; Try adding a leading "/" (common omission in ftp file names).
          ;; Note that this uses oname, which still has any colon part.
@@ -1543,17 +1566,18 @@ which may actually result in an URL rather than a filename."
                (string-match ffap-dired-wildcards name)
                abs
                (ffap-file-exists-string (file-name-directory
-                                         (directory-file-name name)))
+                                         (directory-file-name name))
+                                        nil remote-p)
                name))
          ;; Try all parent directories by deleting the trailing directory
          ;; name until existing directory is found or name stops changing
          ((let ((dir name))
             (while (and dir
-                        (not (ffap-file-exists-string dir))
+                        (not (ffap-file-exists-string dir nil remote-p))
                         (not (equal dir (setq dir (file-name-directory
                                                    (directory-file-name dir)))))))
             (and (not (string= dir "/"))
-                 (ffap-file-exists-string dir))))
+                 (ffap-file-exists-string dir nil remote-p))))
          )
       (set-match-data data))))
 
diff --git a/test/lisp/ffap-tests.el b/test/lisp/ffap-tests.el
index ea5e745bfaf..2bf5d8c79cd 100644
--- a/test/lisp/ffap-tests.el
+++ b/test/lisp/ffap-tests.el
@@ -25,6 +25,7 @@
 
 (require 'cl-lib)
 (require 'ert)
+(require 'tramp)
 (require 'ert-x)
 (require 'ffap)
 
@@ -289,6 +290,27 @@ End of search list.
     (should (member (expand-file-name "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/15.0.0/include")
                     (ffap--c-path)))))
 
+(ert-deftest ffap-test-remote ()
+  (skip-unless
+   (ignore-errors
+     (and
+      (file-remote-p ert-remote-temporary-file-directory)
+      (file-directory-p ert-remote-temporary-file-directory)
+      (file-writable-p ert-remote-temporary-file-directory))))
+  (let* ((ffap-prefer-remote-file t)
+         (default-directory
+          (expand-file-name ert-remote-temporary-file-directory))
+         (test-file (expand-file-name "ffap-test" default-directory)))
+    (with-temp-buffer
+      (ignore-errors (make-empty-file test-file))
+      (insert (file-local-name test-file))
+      (should (equal (ffap-file-at-point) test-file))
+      (erase-buffer)
+      (insert (concat "/usr/bin:" (file-local-name test-file)))
+      (should (equal (ffap-file-at-point) test-file))
+      (delete-file test-file)
+      (should (equal (ffap-file-at-point) default-directory)))))
+
 (provide 'ffap-tests)
 
 ;;; ffap-tests.el ends here