* process.c (Fstart_process):

* callproc.c (Fcall_process): Handle the case where
Funhandled_file_name_directory returns nil.

doc/lispref/files.texi

@@ -2800,10 +2800,12 @@ making connections when they don't exist.
 @end defun
 
 @defun unhandled-file-name-directory filename
-This function returns the name of a directory that is not magic.  It
-uses the directory part of @var{filename} if that is not magic.  For a
-magic file name, it invokes the file name handler, which therefore
-decides what value to return.
+This function returns the name of a directory that is not magic.
+It uses the directory part of @var{filename} if that is not magic.
+For a magic file name, it invokes the file name handler, which
+therefore decides what value to return.  If @var{filename} is not
+accessible from a local process, then the file name handler should
+indicate it by returning nil.
 
 This is useful for running a subprocess; every subprocess must have a
 non-magic directory to serve as its current directory, and this function

src/ChangeLog

 2008-02-06  Stefan Monnier  <monnier@iro.umontreal.ca>
 
+	* process.c (Fstart_process):
+	* callproc.c (Fcall_process): Handle the case where
+	Funhandled_file_name_directory returns nil.
+
 	* font.h (enum lgstring_indices, enum lglyph_indices): New enums.
 	(LGSTRING_SLOT, LGSTRING_SET_SLOT): New macros.
 	* font.c (check_gstring): Use them and AREF to access the vector before

src/callproc.c

@@ -376,9 +376,12 @@ usage: (call-process PROGRAM &optional INFILE BUFFER DISPLAY &rest ARGS)  */)
 
     GCPRO4 (infile, buffer, current_dir, error_file);
 
-    current_dir
-      = expand_and_dir_to_file (Funhandled_file_name_directory (current_dir),
-				Qnil);
+    current_dir = Funhandled_file_name_directory (current_dir);
+    if (NILP (current_dir))
+      /* If the file name handler says that current_dir is unreachable, use
+	 a sensible default. */
+      current_dir = build_string ("~/");
+    current_dir = expand_and_dir_to_file (current_dir, Qnil);
     if (NILP (Ffile_accessible_directory_p (current_dir)))
       report_file_error ("Setting current directory",
 			 Fcons (current_buffer->directory, Qnil));

src/fileio.c

@@ -532,6 +532,8 @@ A `directly usable' directory name is one that may be used without the
 intervention of any file handler.
 If FILENAME is a directly usable file itself, return
 \(file-name-directory FILENAME).
+If FILENAME refers to a file which is not accessible from a local process,
+then this should return nil.
 The `call-process' and `start-process' functions use this function to
 get a current directory to run processes in.  */)
      (filename)

src/process.c

@@ -1614,9 +1614,12 @@ usage: (start-process NAME BUFFER PROGRAM &rest PROGRAM-ARGS)  */)
 
     GCPRO2 (buffer, current_dir);
 
-    current_dir
-      = expand_and_dir_to_file (Funhandled_file_name_directory (current_dir),
-				Qnil);
+    current_dir = Funhandled_file_name_directory (current_dir);
+    if (NILP (current_dir))
+      /* If the file name handler says that current_dir is unreachable, use
+	 a sensible default. */
+      current_dir = build_string ("~/");
+    current_dir = expand_and_dir_to_file (current_dir, Qnil);
     if (NILP (Ffile_accessible_directory_p (current_dir)))
       report_file_error ("Setting current directory",
 			 Fcons (current_buffer->directory, Qnil));