make alias lookup a public, procedural function

This converts git_config_alias to the public alias_lookup
function. Because of the nature of our config parser, we
still have to rely on setting static data. However, that
interface is wrapped so that you can just say

  value = alias_lookup(key);

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

1 files changed, 22 insertions, 0 deletions

diff --git a/alias.c b/alias.c
new file mode 100644
index 000000000..116cac87c
--- /dev/null
+++ b/alias.c
@@ -0,0 +1,22 @@
+#include "cache.h"
+
+static const char *alias_key;
+static char *alias_val;
+static int alias_lookup_cb(const char *k, const char *v)
+{
+	if (!prefixcmp(k, "alias.") && !strcmp(k+6, alias_key)) {
+		if (!v)
+			return config_error_nonbool(k);
+		alias_val = xstrdup(v);
+		return 0;
+	}
+	return 0;
+}
+
+char *alias_lookup(const char *alias)
+{
+	alias_key = alias;
+	alias_val = NULL;
+	git_config(alias_lookup_cb);
+	return alias_val;
+}