Add 'git rev-parse --show-toplevel' option.

Shows the absolute path of the top-level working directory.

Signed-off-by: Steven Drake <sdrake@xnet.co.nz>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-rev-parse.txt

@@ -112,6 +112,9 @@ OPTIONS
 --remotes::
 	Show tag refs found in `$GIT_DIR/refs/remotes`.
 
+--show-toplevel::
+	Show the absolute path of the top-level directory.
+
 --show-prefix::
 	When the command is invoked from a subdirectory, show the
 	path of the current directory relative to the top-level

builtin-rev-parse.c

@@ -581,6 +581,12 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
 				for_each_remote_ref(show_reference, NULL);
 				continue;
 			}
+			if (!strcmp(arg, "--show-toplevel")) {
+				const char *work_tree = get_git_work_tree();
+				if (work_tree)
+					puts(work_tree);
+				continue;
+			}
 			if (!strcmp(arg, "--show-prefix")) {
 				if (prefix)
 					puts(prefix);