Fix DateTimeOffset as Variable

Octokit.GraphQL.Core/Core/Syntax/VariableDefinition.cs

@@ -31,6 +31,10 @@ public static string ToTypeName(Type type, bool isNullable)
             {
                 name = "Boolean";
             }
+            else if (type == typeof(DateTimeOffset))
+            {
+                name = "DateTime";
+            }
             else if (type.IsConstructedGenericType && type.GetGenericTypeDefinition() == typeof(IEnumerable<>))
             {
                 var inner = ToTypeName(type.GenericTypeArguments[0], false);

Octokit.GraphQL.IntegrationTests/Queries/ViewerTests.cs

@@ -1,4 +1,6 @@
-using System.Linq;
+using System;
+using System.Collections.Generic;
+using System.Linq;
 using System.Threading.Tasks;
 using Octokit.GraphQL.Core;
 using Octokit.GraphQL.IntegrationTests.Utilities;
@@ -88,5 +90,23 @@ public async Task Viewer_Has_No_OrganizationVerifiedDomainEmails_For_Octokit()
 
             Assert.Empty(emails);
         }
+
+        [IntegrationTest]
+        public async Task DateTime_Filter_Works()
+        {
+            var query = new GraphQL.Query()
+                        .Viewer.ContributionsCollection(from: Variable.Var("start"))
+                        .Select(c => c.User.Name);
+
+            var vars = new Dictionary<string, object>
+            {
+                { "start", new DateTimeOffset(2000, 1, 2, 3, 4, 5, default) }
+            };
+
+            var response = await Connection.Run(query.Compile(), vars);
+
+            // no server error
+            Assert.NotNull(response);
+        }
     }
 }

Octokit.GraphQL.UnitTests/QueryBuilderTests.cs

@@ -317,5 +317,26 @@ ... on User {
 
             Assert.Equal(expected, query.ToString(), ignoreLineEndingDifferences: true);
         }
+
+        [Fact]
+        public void DateTimeOffsetVariable()
+        {
+            var expected = @"query($start: DateTime) {
+  user(login: ""grokys"") {
+    contributionsCollection(from: $start) {
+      latestRestrictedContributionDate
+    }
+  }
+}";
+
+            var expression = new Query()
+                             .User("grokys")
+                             .ContributionsCollection(@from: Variable.Var("start"))
+                             .Select(c => c.LatestRestrictedContributionDate);
+
+            var query = expression.Compile();
+
+            Assert.Equal(expected, query.ToString(), ignoreLineEndingDifferences: true);
+        }
     }
 }