add refname_match()

We use at least two rulesets for matching abbreviated refnames with
full refnames (starting with 'refs/').  git-rev-parse and git-fetch
use slightly different rules.

This commit introduces a new function refname_match
(const char *abbrev_name, const char *full_name, const char **rules).

abbrev_name is expanded using the rules and matched against full_name.
If a match is found the function returns true.  rules is a NULL-terminate
list of format patterns with "%.*s", for example:

    const char *ref_rev_parse_rules[] = {
               "%.*s",
               "refs/%.*s",
               "refs/tags/%.*s",
               "refs/heads/%.*s",
               "refs/remotes/%.*s",
               "refs/remotes/%.*s/HEAD",
               NULL
    };

Asterisks are included in the format strings because this is the form
required in sha1_name.c.  Sharing the list with the functions there is
a good idea to avoid duplicating the rules.  Hopefully this
facilitates unified matching rules in the future.

This commit makes the rules used by rev-parse for resolving refs to
sha1s available for string comparison.  Before this change, the rules
were buried in get_sha1*() and dwim_ref().

A follow-up commit will refactor the rules used by fetch.

refname_match() will be used for matching refspecs in git-send-pack.

Thanks to Daniel Barkalow <barkalow@iabervon.org> for pointing
out that ref_matches_abbrev in remote.c solves a similar problem
and care should be taken to avoid confusion.

Signed-off-by: Steffen Prohaska <prohaska@zib.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/cache.h b/cache.h
index 33ebccf..38d9a28 100644
--- a/cache.h
+++ b/cache.h
@@ -415,6 +415,9 @@
 extern int dwim_ref(const char *str, int len, unsigned char *sha1, char **ref);
 extern int dwim_log(const char *str, int len, unsigned char *sha1, char **ref);
 
+extern int refname_match(const char *abbrev_name, const char *full_name, const char **rules);
+extern const char *ref_rev_parse_rules[];
+
 extern int create_symref(const char *ref, const char *refs_heads_master, const char *logmsg);
 extern int validate_headref(const char *ref);