Ensure 'call-process' interprets INFILE as a local path

* src/callproc.c (get_current_directory): Rename from
'encode_current_directory' and add boolean ENCODE flag.
(Fcall_process): Interpret INFILE relative to the working directory
from which PROGRAM is run, not 'default-directory'.
(call_process): Use 'get_current_directory'.
* src/process.c (Fmake_process): Use 'get_current_directory'.
* src/process.h (get_current_directory): Rename decl from
'encode_current_directory'.
* src/sysdep.c (sys_subshell): Use 'get_current_directory' (bug#49283).

src/callproc.c

@@ -116,11 +116,13 @@ static CHILD_SETUP_TYPE child_setup (int, int, int, char **, char **,
 				     const char *);
 
 /* Return the current buffer's working directory, or the home
-   directory if it's unreachable, as a string suitable for a system call.
-   Signal an error if the result would not be an accessible directory.  */
+   directory if it's unreachable.  If ENCODE is true, return as a string
+   suitable for a system call; otherwise, return a string in its
+   internal representation.  Signal an error if the result would not be
+   an accessible directory.  */
 
 Lisp_Object
-encode_current_directory (void)
+get_current_directory (bool encode)
 {
   Lisp_Object curdir = BVAR (current_buffer, directory);
   Lisp_Object dir = Funhandled_file_name_directory (curdir);
@@ -131,12 +133,12 @@ encode_current_directory (void)
     dir = build_string ("~");
 
   dir = expand_and_dir_to_file (dir);
-  dir = ENCODE_FILE (remove_slash_colon (dir));
+  Lisp_Object encoded_dir = ENCODE_FILE (remove_slash_colon (dir));
 
-  if (! file_accessible_directory_p (dir))
+  if (! file_accessible_directory_p (encoded_dir))
     report_file_error ("Setting current directory", curdir);
 
-  return dir;
+  return encode ? encoded_dir : dir;
 }
 
 /* If P is reapable, record it as a deleted process and kill it.
@@ -225,8 +227,9 @@ DEFUN ("call-process", Fcall_process, Scall_process, 1, MANY, 0,
 The remaining arguments are optional.
 
 The program's input comes from file INFILE (nil means `null-device').
-If you want to make the input come from an Emacs buffer, use
-`call-process-region' instead.
+If INFILE is a relative path, it will be looked for relative to the
+directory where the process is run (see below).  If you want to make the
+input come from an Emacs buffer, use `call-process-region' instead.
 
 Third argument DESTINATION specifies how to handle program's output.
 If DESTINATION is a buffer, or t that stands for the current buffer,
@@ -270,7 +273,9 @@ usage: (call-process PROGRAM &optional INFILE DESTINATION DISPLAY &rest ARGS)  *
 
   if (nargs >= 2 && ! NILP (args[1]))
     {
-      infile = Fexpand_file_name (args[1], BVAR (current_buffer, directory));
+      /* Expand infile relative to the current buffer's current
+	 directory, or its unhandled equivalent ("~").  */
+      infile = Fexpand_file_name (args[1], get_current_directory (false));
       CHECK_STRING (infile);
     }
   else
@@ -439,7 +444,7 @@ call_process (ptrdiff_t nargs, Lisp_Object *args, int filefd,
      buffer's current directory, or its unhandled equivalent.  We
      can't just have the child check for an error when it does the
      chdir, since it's in a vfork.  */
-  current_dir = encode_current_directory ();
+  current_dir = get_current_directory (true);
 
   if (STRINGP (error_file))
     {

src/process.c

@@ -1755,7 +1755,7 @@ usage: (make-process &rest ARGS)  */)
      buffer's current directory, or its unhandled equivalent.  We
      can't just have the child check for an error when it does the
      chdir, since it's in a vfork.  */
-  current_dir = encode_current_directory ();
+  current_dir = get_current_directory (true);
 
   name = Fplist_get (contact, QCname);
   CHECK_STRING (name);

src/process.h

@@ -264,7 +264,7 @@ enum
 
 /* Defined in callproc.c.  */
 
-extern Lisp_Object encode_current_directory (void);
+extern Lisp_Object get_current_directory (bool);
 extern void record_kill_process (struct Lisp_Process *, Lisp_Object);
 
 /* Defined in sysdep.c.  */

src/sysdep.c

@@ -657,7 +657,7 @@ sys_subshell (void)
 #endif
   pid_t pid;
   struct save_signal saved_handlers[5];
-  char *str = SSDATA (encode_current_directory ());
+  char *str = SSDATA (get_current_directory (true));
 
 #ifdef DOS_NT
   pid = 0;