Merge branch 'js/maint-submodule-checkout' into maint

* js/maint-submodule-checkout:
  Fix 'git checkout <submodule>' to update the index

builtin-checkout.c

@@ -53,9 +53,6 @@ static int update_some(const unsigned char *sha1, const char *base, int baselen,
 	int len;
 	struct cache_entry *ce;
 
-	if (S_ISGITLINK(mode))
-		return 0;
-
 	if (S_ISDIR(mode))
 		return READ_TREE_RECURSIVE;
 

t/t2013-checkout-submodule.sh

@@ -0,0 +1,42 @@
+#!/bin/sh
+
+test_description='checkout can handle submodules'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	mkdir submodule &&
+	(cd submodule &&
+	 git init &&
+	 test_commit first) &&
+	git add submodule &&
+	test_tick &&
+	git commit -m superproject &&
+	(cd submodule &&
+	 test_commit second) &&
+	git add submodule &&
+	test_tick &&
+	git commit -m updated.superproject
+'
+
+test_expect_success '"reset <submodule>" updates the index' '
+	git update-index --refresh &&
+	git diff-files --quiet &&
+	git diff-index --quiet --cached HEAD &&
+	test_must_fail git reset HEAD^ submodule &&
+	test_must_fail git diff-files --quiet &&
+	git reset submodule &&
+	git diff-files --quiet
+'
+
+test_expect_success '"checkout <submodule>" updates the index only' '
+	git update-index --refresh &&
+	git diff-files --quiet &&
+	git diff-index --quiet --cached HEAD &&
+	git checkout HEAD^ submodule &&
+	test_must_fail git diff-files --quiet &&
+	git checkout HEAD submodule &&
+	git diff-files --quiet
+'
+
+test_done