Disallow empty section and variable names

It is possible to break your repository config by creating an invalid key.  The
config parser in turn chokes on it:

  $ git init
  Initialized empty Git repository in /tmp/gittest/.git/
  $ git config .foo false
  $ git config core.bare
  fatal: bad config file line 6 in .git/config

This patch makes git-config reject keys which start or end with a dot and adds
tests for these cases.

Signed-off-by: Libor Pechacek <lpechacek@suse.cz>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

config.c

@@ -1120,11 +1120,16 @@ int git_config_parse_key(const char *key, char **store_key, int *baselen_)
 	 * key name separated by a dot, we have to know where the dot is.
 	 */
 
-	if (last_dot == NULL) {
+	if (last_dot == NULL || last_dot == key) {
 		error("key does not contain a section: %s", key);
 		return -2;
 	}
 
+	if (!last_dot[1]) {
+		error("key does not contain variable name: %s", key);
+		return -2;
+	}
+
 	baselen = last_dot - key;
 	if (baselen_)
 		*baselen_ = baselen;

t/t1300-repo-config.sh

@@ -889,6 +889,10 @@ test_expect_success 'key sanity-checking' '
 	test_must_fail git config foo.1bar &&
 	test_must_fail git config foo."ba
 				z".bar &&
+	test_must_fail git config . false &&
+	test_must_fail git config .foo false &&
+	test_must_fail git config foo. false &&
+	test_must_fail git config .foo. false &&
 	git config foo.bar true &&
 	git config foo."ba =z".bar false
 '