refs: break out ref conflict checks

Create new function find_descendant_ref, to hold one of the ref
conflict checks used in verify_refname_available. Multiple backends
will need this function, so move it to the common code.

Also move rename_ref_available to the common code, because alternate
backends might need it and it has no files-backend-specific code.

Signed-off-by: David Turner <dturner@twopensource.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Jeff King <peff@peff.net>

refs.c

@@ -1029,3 +1029,47 @@ int ref_is_hidden(const char *refname)
 	}
 	return 0;
 }
+
+const char *find_descendant_ref(const char *dirname,
+				const struct string_list *extras,
+				const struct string_list *skip)
+{
+	int pos;
+
+	if (!extras)
+		return NULL;
+
+	/*
+	 * Look at the place where dirname would be inserted into
+	 * extras. If there is an entry at that position that starts
+	 * with dirname (remember, dirname includes the trailing
+	 * slash) and is not in skip, then we have a conflict.
+	 */
+	for (pos = string_list_find_insert_index(extras, dirname, 0);
+	     pos < extras->nr; pos++) {
+		const char *extra_refname = extras->items[pos].string;
+
+		if (!starts_with(extra_refname, dirname))
+			break;
+
+		if (!skip || !string_list_has_string(skip, extra_refname))
+			return extra_refname;
+	}
+	return NULL;
+}
+
+int rename_ref_available(const char *oldname, const char *newname)
+{
+	struct string_list skip = STRING_LIST_INIT_NODUP;
+	struct strbuf err = STRBUF_INIT;
+	int ret;
+
+	string_list_insert(&skip, oldname);
+	ret = !verify_refname_available(newname, NULL, &skip, &err);
+	if (!ret)
+		error("%s", err.buf);
+
+	string_list_clear(&skip, 0);
+	strbuf_release(&err);
+	return ret;
+}

refs/files-backend.c

@@ -728,6 +728,7 @@ static int verify_refname_available_dir(const char *refname,
 					struct strbuf *err)
 {
 	const char *slash;
+	const char *extra_refname;
 	int pos;
 	struct strbuf dirname = STRBUF_INIT;
 	int ret = -1;
@@ -833,32 +834,12 @@ static int verify_refname_available_dir(const char *refname,
 		}
 	}
 
-	if (extras) {
-		/*
-		 * Check for entries in extras that start with
-		 * "$refname/". We do that by looking for the place
-		 * where "$refname/" would be inserted in extras. If
-		 * there is an entry at that position that starts with
-		 * "$refname/" and is not in skip, then we have a
-		 * conflict.
-		 */
-		for (pos = string_list_find_insert_index(extras, dirname.buf, 0);
-		     pos < extras->nr; pos++) {
-			const char *extra_refname = extras->items[pos].string;
-
-			if (!starts_with(extra_refname, dirname.buf))
-				break;
-
-			if (!skip || !string_list_has_string(skip, extra_refname)) {
-				strbuf_addf(err, "cannot process '%s' and '%s' at the same time",
-					    refname, extra_refname);
-				goto cleanup;
-			}
-		}
-	}
-
-	/* No conflicts were found */
-	ret = 0;
+	extra_refname = find_descendant_ref(dirname.buf, extras, skip);
+	if (extra_refname)
+		strbuf_addf(err, "cannot process '%s' and '%s' at the same time",
+			    refname, extra_refname);
+	else
+		ret = 0;
 
 cleanup:
 	strbuf_release(&dirname);
@@ -2473,22 +2454,6 @@ int verify_refname_available(const char *newname,
 	return 0;
 }
 
-static int rename_ref_available(const char *oldname, const char *newname)
-{
-	struct string_list skip = STRING_LIST_INIT_NODUP;
-	struct strbuf err = STRBUF_INIT;
-	int ret;
-
-	string_list_insert(&skip, oldname);
-	ret = !verify_refname_available(newname, NULL, &skip, &err);
-	if (!ret)
-		error("%s", err.buf);
-
-	string_list_clear(&skip, 0);
-	strbuf_release(&err);
-	return ret;
-}
-
 static int write_ref_to_lockfile(struct ref_lock *lock,
 				 const unsigned char *sha1, struct strbuf *err);
 static int commit_ref_update(struct ref_lock *lock,

refs/refs-internal.h

@@ -181,4 +181,20 @@ int files_log_ref_write(const char *refname, const unsigned char *old_sha1,
 			const unsigned char *new_sha1, const char *msg,
 			int flags, struct strbuf *err);
 
+/*
+ * Check for entries in extras that are within the specified
+ * directory, where dirname is a reference directory name including
+ * the trailing slash (e.g., "refs/heads/foo/"). Ignore any
+ * conflicting references that are found in skip. If there is a
+ * conflicting reference, return its name.
+ *
+ * extras and skip must be sorted lists of reference names. Either one
+ * can be NULL, signifying the empty list.
+ */
+const char *find_descendant_ref(const char *dirname,
+				const struct string_list *extras,
+				const struct string_list *skip);
+
+int rename_ref_available(const char *oldname, const char *newname);
+
 #endif /* REFS_REFS_INTERNAL_H */