Fixed collect fields issue.

src/Core/Core.Tests/Execution/ResolverContextTests.cs

@@ -1,6 +1,10 @@
 using System.Threading.Tasks;
 using Xunit;
 using Snapshooter.Xunit;
+using HotChocolate.Resolvers;
+using System.Collections.Generic;
+using HotChocolate.Types;
+using System.Linq;
 
 namespace HotChocolate.Execution
 {
@@ -53,5 +57,72 @@ public async Task AccessVariables_Failes_When_Variable_Not_Exists()
             // assert
             result.MatchSnapshot();
         }
+
+        [Fact]
+        public async Task CollectFields()
+        {
+            // arrange
+            var list = new List<IFieldSelection>();
+
+            ISchema schema = SchemaBuilder.New()
+                .AddDocumentFromString(
+                    @"
+                    type Query {
+                        foo: Foo
+                    }
+
+                    type Foo {
+                        bar: Bar
+                    }
+
+                    type Bar {
+                        baz: String
+                    }")
+                .Use(next => context =>
+                {
+                    if (context.Field.Type.NamedType() is ObjectType type)
+                    {
+                        foreach (IFieldSelection selection in context.CollectFields(type))
+                        {
+                            CollectSelections(context, selection, list);
+                        }
+                    }
+                    return Task.CompletedTask;
+                })
+                .Create();
+
+            // act
+            await schema.MakeExecutable().ExecuteAsync(
+            @"{
+                foo {
+                    bar {
+                        baz
+                    }
+                }
+            }");
+
+            // assert
+            list.Select(t => t.Selection.Name.Value).ToList().MatchSnapshot();
+        }
+
+        private static void CollectSelections(
+            IResolverContext context,
+            IFieldSelection selection,
+            ICollection<IFieldSelection> collected)
+        {
+            if (selection.Field.Type.IsLeafType())
+            {
+                collected.Add(selection);
+            }
+
+            if (selection.Field.Type.NamedType() is ObjectType objectType)
+            {
+                foreach (IFieldSelection child in context.CollectFields(
+                    objectType, selection.Selection.SelectionSet))
+                {
+                    CollectSelections(context, child, collected);
+                }
+            }
+        }
     }
 }

src/Core/Core.Tests/Execution/__snapshots__/ResolverContextTests.CollectFields.snap

@@ -0,0 +1,3 @@
+[
+  "baz"
+]

src/Core/Core/Execution/Utilities/ResolverContext.cs

@@ -224,13 +224,11 @@ public async Task<T> ResolveAsync<T>()
 
         public IReadOnlyCollection<FieldSelection> CollectFields(
             ObjectType typeContext) =>
-            _executionContext.CollectFields(
-                typeContext, FieldSelection.SelectionSet, Path);
+            CollectFields(typeContext, FieldSelection.SelectionSet);
 
         public IReadOnlyCollection<FieldSelection> CollectFields(
             ObjectType typeContext, SelectionSetNode selectionSet) =>
-            _executionContext.CollectFields(
-                typeContext, FieldSelection.SelectionSet, Path);
+            _executionContext.CollectFields(typeContext, selectionSet, Path);
 
         IReadOnlyCollection<IFieldSelection> IResolverContext.CollectFields(
             ObjectType typeContext) => CollectFields(typeContext);