recursive submodules: test for relative paths

"git submodule update --init --recursive" uses full path to refer to
the true location of the repository in the "gitdir:" pointer for
nested submodules; the command used to use relative paths.

This was reported by Norio Nomura in $gmane/290280.

The root cause for that bug is in using recursive submodules as
their relative path handling was broken in ee8838d (2015-09-08,
submodule: rewrite `module_clone` shell function in C).

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7400-submodule-basic.sh

@@ -818,6 +818,47 @@ test_expect_success 'submodule add --name allows to replace a submodule with ano
 	)
 '
 
+test_expect_failure 'recursive relative submodules stay relative' '
+	test_when_finished "rm -rf super clone2 subsub sub3" &&
+	mkdir subsub &&
+	(
+		cd subsub &&
+		git init &&
+		>t &&
+		git add t &&
+		git commit -m "initial commit"
+	) &&
+	mkdir sub3 &&
+	(
+		cd sub3 &&
+		git init &&
+		>t &&
+		git add t &&
+		git commit -m "initial commit" &&
+		git submodule add ../subsub dirdir/subsub &&
+		git commit -m "add submodule subsub"
+	) &&
+	mkdir super &&
+	(
+		cd super &&
+		git init &&
+		>t &&
+		git add t &&
+		git commit -m "initial commit" &&
+		git submodule add ../sub3 &&
+		git commit -m "add submodule sub"
+	) &&
+	git clone super clone2 &&
+	(
+		cd clone2 &&
+		git submodule update --init --recursive &&
+		echo "gitdir: ../.git/modules/sub3" >./sub3/.git_expect &&
+		echo "gitdir: ../../../.git/modules/sub3/modules/dirdir/subsub" >./sub3/dirdir/subsub/.git_expect
+	) &&
+	test_cmp clone2/sub3/.git_expect clone2/sub3/.git &&
+	test_cmp clone2/sub3/dirdir/subsub/.git_expect clone2/sub3/dirdir/subsub/.git
+'
+
 test_expect_success 'submodule add with an existing name fails unless forced' '
 	(
 		cd addtest2 &&