config: complain about --local outside of a git repo

The "--local" option instructs git-config to read or modify
the repository-level config. This doesn't make any sense if
you're not actually in a repository.

Older versions of Git would blindly try to read or write
".git/config". For reading, this would result in a quiet
failure, since there was no config to read (and thus no
matching config value). Writing would generally fail
noisily, since ".git" was unlikely to exist. But since
b1ef400ee (setup_git_env: avoid blind fall-back to ".git",
2016-10-20), we catch this in the call to git_pathdup() and
die with an assertion.

Dying is the right thing to do, but we should catch the
problem early and give a more human-friendly error message.

Note that even without --local, git-config will sometimes
default to using local repository config (e.g., when
writing). These cases are already protected by similar
checks, and covered by a test in t1308.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/config.c

@@ -496,6 +496,9 @@ int cmd_config(int argc, const char **argv, const char *prefix)
 		usage_with_options(builtin_config_usage, builtin_config_options);
 	}
 
+	if (use_local_config && nongit)
+		die(_("--local can only be used inside a git repository"));
+
 	if (given_config_source.file &&
 			!strcmp(given_config_source.file, "-")) {
 		given_config_source.file = NULL;

t/t1300-repo-config.sh

@@ -1539,7 +1539,7 @@ test_expect_success !MINGW '--show-origin blob ref' '
 	test_cmp expect output
 '
 
-test_expect_failure '--local requires a repo' '
+test_expect_success '--local requires a repo' '
 	# we expect 128 to ensure that we do not simply
 	# fail to find anything and return code "1"
 	test_expect_code 128 nongit git config --local foo.bar