Restore pane_current_path format from portable tmux, it is no longer

used by default and is very useful.

format.c

@@ -741,6 +741,21 @@ format_cb_current_command(struct format_tree *ft, struct format_entry *fe)
 	free(cmd);
 }
 
+/* Callback for pane_current_path. */
+static void
+format_cb_current_path(struct format_tree *ft, struct format_entry *fe)
+{
+	struct window_pane	*wp = ft->wp;
+	char			*cwd;
+
+	if (wp == NULL)
+		return;
+
+	cwd = get_proc_cwd(wp->fd);
+	if (cwd != NULL)
+		fe->value = xstrdup(cwd);
+}
+
 /* Callback for history_bytes. */
 static void
 format_cb_history_bytes(struct format_tree *ft, struct format_entry *fe)
@@ -2722,6 +2737,7 @@ format_defaults_pane(struct format_tree *ft, struct window_pane *wp)
 	format_add(ft, "pane_pid", "%ld", (long) wp->pid);
 	format_add_cb(ft, "pane_start_command", format_cb_start_command);
 	format_add_cb(ft, "pane_current_command", format_cb_current_command);
+	format_add_cb(ft, "pane_current_path", format_cb_current_path);
 
 	format_add(ft, "cursor_x", "%u", wp->base.cx);
 	format_add(ft, "cursor_y", "%u", wp->base.cy);

procname.c

@@ -38,6 +38,7 @@
 
 static struct kinfo_proc *cmp_procs(struct kinfo_proc *, struct kinfo_proc *);
 char	*get_proc_name(int, char *);
+char	*get_proc_cwd(int);
 
 static struct kinfo_proc *
 cmp_procs(struct kinfo_proc *p1, struct kinfo_proc *p2)
@@ -132,3 +133,17 @@ error:
 	free(buf);
 	return (NULL);
 }
+
+char *
+get_proc_cwd(int fd)
+{
+        int             name[] = { CTL_KERN, KERN_PROC_CWD, 0 };
+        static char     path[MAXPATHLEN];
+        size_t          pathlen = sizeof path;
+
+        if ((name[2] = tcgetpgrp(fd)) == -1)
+                return (NULL);
+        if (sysctl(name, 3, path, &pathlen, NULL, 0) != 0)
+                return (NULL);
+        return (path);
+}

tmux.1

@@ -4409,6 +4409,7 @@ The following variables are available, where appropriate:
 .It Li "pane_at_top" Ta "" Ta "1 if pane is at the top of window"
 .It Li "pane_bottom" Ta "" Ta "Bottom of pane"
 .It Li "pane_current_command" Ta "" Ta "Current command if available"
+.It Li "pane_current_path" Ta "" Ta "Current path if available"
 .It Li "pane_dead" Ta "" Ta "1 if pane is dead"
 .It Li "pane_dead_status" Ta "" Ta "Exit status of process in dead pane"
 .It Li "pane_format" Ta "" Ta "1 if format is for a pane"

tmux.h

@@ -2743,6 +2743,7 @@ int		 utf8_cstrhas(const char *, const struct utf8_data *);
 
 /* procname.c */
 char   *get_proc_name(int, char *);
+char   *get_proc_cwd(int);
 
 /* log.c */
 void	log_add_level(void);