Prevent repo.Lookup() to accept GitLink as a target type

1 files changed, 14 insertions, 0 deletions

diff --git a/LibGit2Sharp/RepositoryExtensions.cs b/LibGit2Sharp/RepositoryExtensions.cs
index c653e9fe..ae62fab2 100644
--- a/LibGit2Sharp/RepositoryExtensions.cs
+++ b/LibGit2Sharp/RepositoryExtensions.cs
@@ -21,6 +21,8 @@ namespace LibGit2Sharp
         /// <returns></returns>
         public static T Lookup<T>(this IRepository repository, string objectish) where T : GitObject
         {
+            EnsureNoGitLink<T>();
+
             return (T)repository.Lookup(objectish, GitObject.TypeToTypeMap[typeof (T)]);
         }
 
@@ -33,9 +35,21 @@ namespace LibGit2Sharp
         /// <returns></returns>
         public static T Lookup<T>(this IRepository repository, ObjectId id) where T : GitObject
         {
+            EnsureNoGitLink<T>();
+
             return (T)repository.Lookup(id, GitObject.TypeToTypeMap[typeof(T)]);
         }
 
+        private static void EnsureNoGitLink<T>() where T : GitObject
+        {
+            if (typeof(T) != typeof(GitLink))
+            {
+                return;
+            }
+
+            throw new ArgumentException("A GitObject of type 'GitLink' cannot be looked up.");
+        }
+
         /// <summary>
         ///   Creates a lightweight tag with the specified name. This tag will point at the commit pointed at by the <see cref = "Repository.Head" />.
         /// </summary>