Provide the OID whose lookup failed in the error

Author: tiennou

ObjectiveGit/Categories/NSError+Git.h

@@ -29,8 +29,12 @@
 
 #import <Foundation/Foundation.h>
 
+/// The error domain used by Objective-Git
 extern NSString * const GTGitErrorDomain;
 
+/// Error userinfo keys
+extern NSString * const GTGitErrorOID;
+
 @interface NSError (Git)
 
 /// Describes the given libgit2 error code, using any message provided by

ObjectiveGit/Categories/NSError+Git.m

@@ -31,6 +31,7 @@
 #import "git2/errors.h"
 
 NSString * const GTGitErrorDomain = @"GTGitErrorDomain";
+NSString * const GTGitErrorOID = @"GTOID";
 
 @implementation NSError (Git)
 

ObjectiveGit/GTRepository.m

@@ -290,7 +290,10 @@ - (id)lookUpObjectByGitOid:(const git_oid *)oid objectType:(GTObjectType)type er
 		if (error != NULL) {
 			char oid_str[GIT_OID_HEXSZ+1];
 			git_oid_tostr(oid_str, sizeof(oid_str), oid);
-			*error = [NSError git_errorFor:gitError description:@"Failed to lookup object %s in repository.", oid_str];
+			*error = [NSError git_errorFor:gitError
+							   description:@"Failed to lookup object"
+								  userInfo:@{GTGitErrorOID: [GTOID oidWithGitOid:oid]}
+							 failureReason:@"The object %s couldn't be found in the repository.", oid_str];
 		}
 		return nil;
 	}