submodules: always use a relative path from gitdir to work tree

Since recently a submodule with name <name> has its git directory in the
.git/modules/<name> directory of the superproject while the work tree
contains a gitfile pointing there. To make that work the git directory has
the core.worktree configuration set in its config file to point back to
the work tree.

That core.worktree is an absolute path set by the initial clone of the
submodule. A relative path is preferable here because it allows the
superproject to be moved around without invalidating that setting, so
compute and set that relative path after cloning or reactivating the
submodule.

This also fixes a bug when moving a submodule around inside the
superproject, as the current code forgot to update the setting to the new
submodule work tree location.

Enhance t7400 to ensure that future versions won't re-add absolute paths
by accident and that moving a superproject won't break submodules.

Signed-off-by: Jens Lehmann <Jens.Lehmann@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-submodule.sh

@@ -169,6 +169,24 @@ module_clone()
 	fi
 
 	echo "gitdir: $rel_gitdir" >"$path/.git"
+
+	a=$(cd "$gitdir" && pwd)/
+	b=$(cd "$path" && pwd)/
+	# Remove all common leading directories after a sanity check
+	if test "${a#$b}" != "$a" || test "${b#$a}" != "$b"; then
+		die "$(eval_gettext "Gitdir '\$a' is part of the submodule path '\$b' or vice versa")"
+	fi
+	while test "${a%%/*}" = "${b%%/*}"
+	do
+		a=${a#*/}
+		b=${b#*/}
+	done
+	# Now chop off the trailing '/'s that were added in the beginning
+	a=${a%/}
+	b=${b%/}
+
+	rel=$(echo $a | sed -e 's|[^/]*|..|g')
+	(clear_local_git_env; cd "$path" && GIT_WORK_TREE=. git config core.worktree "$rel/$b")
 }
 
 #

t/t7400-submodule-basic.sh

@@ -81,6 +81,13 @@ test_expect_success 'submodule add' '
 		test ! -s actual &&
 		echo "gitdir: ../.git/modules/submod" >expect &&
 		test_cmp expect submod/.git &&
+		(
+			cd submod &&
+			git config core.worktree >actual &&
+			echo "../../../submod" >expect &&
+			test_cmp expect actual &&
+			rm -f actual expect
+		) &&
 		git submodule init
 	) &&
 
@@ -500,4 +507,17 @@ test_expect_success 'relative path works with user@host:path' '
 	)
 '
 
+test_expect_success 'moving the superproject does not break submodules' '
+	(
+		cd addtest &&
+		git submodule status >expect
+	)
+	mv addtest addtest2 &&
+	(
+		cd addtest2 &&
+		git submodule status >actual &&
+		test_cmp expect actual
+	)
+'
+
 test_done