submodules: don't stumble over symbolic links when cloning recursively

Since 69c30517 (submodules: refactor computation of relative gitdir path)
cloning a submodule recursively fails for nested submodules when a
symbolic link is part of the path to the work tree of the superproject.

This happens when module_clone() tries to find the relative paths between
the work tree and the git dir. When a symbolic link in current $PWD points
to a directory that is at a different level, then determining the number
of "../" needed to traverse to the superproject's work tree leads to a
wrong result.

As there is no portable way to say "pwd -P", use cd_to_toplevel to remove
the link from $PWD, which fixes this problem.

A test for this issue has been added to t7406.
Reported-by: NBob Halley <halley@play-bow.org>
Signed-off-by: NJens Lehmann <Jens.Lehmann@web.de>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

git-submodule.sh

@@ -149,8 +149,10 @@ module_clone()
 		die "$(eval_gettext "Clone of '\$url' into submodule path '\$path' failed")"
 	fi
 
-	a=$(cd "$gitdir" && pwd)/
-	b=$(cd "$path" && pwd)/
+	# We already are at the root of the work tree but cd_to_toplevel will
+	# resolve any symlinks that might be present in $PWD
+	a=$(cd_to_toplevel && cd "$gitdir" && pwd)/
+	b=$(cd_to_toplevel && cd "$path" && pwd)/
 	# normalize Windows-style absolute paths to POSIX-style absolute paths
 	case $a in [a-zA-Z]:/*) a=/${a%%:*}${a#*:} ;; esac
 	case $b in [a-zA-Z]:/*) b=/${b%%:*}${b#*:} ;; esac

t/t7406-submodule-update.sh

@@ -636,4 +636,17 @@ test_expect_success 'submodule update properly revives a moved submodule' '
 	)
 '
 
+test_expect_success SYMLINKS 'submodule update can handle symbolic links in pwd' '
+	mkdir -p linked/dir &&
+	ln -s linked/dir linkto &&
+	(
+		cd linkto &&
+		git clone "$TRASH_DIRECTORY"/super_update_r2 super &&
+		(
+			cd super &&
+			git submodule update --init --recursive
+		)
+	)
+'
+
 test_done