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>

cache.h

@@ -415,6 +415,9 @@ extern const char *resolve_ref(const char *path, unsigned char *sha1, int, int *
 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);
 

refs.c

@@ -643,6 +643,30 @@ int check_ref_format(const char *ref)
 	}
 }
 
+const char *ref_rev_parse_rules[] = {
+	"%.*s",
+	"refs/%.*s",
+	"refs/tags/%.*s",
+	"refs/heads/%.*s",
+	"refs/remotes/%.*s",
+	"refs/remotes/%.*s/HEAD",
+	NULL
+};
+
+int refname_match(const char *abbrev_name, const char *full_name, const char **rules)
+{
+	const char **p;
+	const int abbrev_name_len = strlen(abbrev_name);
+
+	for (p = rules; *p; p++) {
+		if (!strcmp(full_name, mkpath(*p, abbrev_name_len, abbrev_name))) {
+			return 1;
+		}
+	}
+
+	return 0;
+}
+
 static struct ref_lock *verify_lock(struct ref_lock *lock,
 	const unsigned char *old_sha1, int mustexist)
 {

sha1_name.c

@@ -239,23 +239,13 @@ static int ambiguous_path(const char *path, int len)
 	return slash;
 }
 
-static const char *ref_fmt[] = {
-	"%.*s",
-	"refs/%.*s",
-	"refs/tags/%.*s",
-	"refs/heads/%.*s",
-	"refs/remotes/%.*s",
-	"refs/remotes/%.*s/HEAD",
-	NULL
-};
-
 int dwim_ref(const char *str, int len, unsigned char *sha1, char **ref)
 {
 	const char **p, *r;
 	int refs_found = 0;
 
 	*ref = NULL;
-	for (p = ref_fmt; *p; p++) {
+	for (p = ref_rev_parse_rules; *p; p++) {
 		unsigned char sha1_from_ref[20];
 		unsigned char *this_result;
 
@@ -277,7 +267,7 @@ int dwim_log(const char *str, int len, unsigned char *sha1, char **log)
 	int logs_found = 0;
 
 	*log = NULL;
-	for (p = ref_fmt; *p; p++) {
+	for (p = ref_rev_parse_rules; *p; p++) {
 		struct stat st;
 		unsigned char hash[20];
 		char path[PATH_MAX];