Update selection path with type refinement

Author: tobias-tengler

src/HotChocolate/Fusion-vnext/src/Fusion.Execution/Planning/OperationDefinitionBuilder.cs

@@ -12,6 +12,7 @@ internal sealed class OperationDefinitionBuilder
     private string? _name;
     private string? _description;
     private Lookup? _lookup;
+    private bool _isAbstractLookup;
     private string? _requirementKey;
     private SelectionSetNode? _selectionSet;
 
@@ -40,9 +41,10 @@ public OperationDefinitionBuilder SetDescription(string? description)
         return this;
     }
 
-    public OperationDefinitionBuilder SetLookup(Lookup? lookup, string? requirementKey)
+    public OperationDefinitionBuilder SetLookup(Lookup? lookup, bool isAbstractLookup, string? requirementKey)
     {
         _lookup = lookup;
+        _isAbstractLookup = isAbstractLookup;
         _requirementKey = requirementKey;
         return this;
     }
@@ -88,6 +90,11 @@ public OperationDefinitionBuilder SetSelectionSet(SelectionSetNode selectionSet)
             indexBuilder.Register(selectionSet);
             index = indexBuilder;
             selectionPath = selectionPath.AppendField(_lookup.FieldName);
+
+            if (_isAbstractLookup)
+            {
+                selectionPath = selectionPath.AppendFragment(_lookup.FieldType);
+            }
         }
 
         var definition = new OperationDefinitionNode(

src/HotChocolate/Fusion-vnext/src/Fusion.Execution/Planning/OperationPlanner.cs

@@ -293,10 +293,11 @@ lookup is null
                 requirements = requirements.Add(argumentRequirementKey, operationRequirement);
             }
 
-            // If the lookup returns an abstract type, we might need to insert a type refinement
-            // around our selection set.
+            var isAbstractLookup = false;
             if (_schema.Types.TryGetType(lookup.FieldType, out var lookupFieldType)
-                && lookupFieldType != workItem.SelectionSet.Type)
+                && lookupFieldType != workItem.SelectionSet.Type
+                && !resolvable.Selections.All(s => s is InlineFragmentNode inlineFragment
+                    && inlineFragment.TypeCondition?.Name.Value == workItem.SelectionSet.Type.Name))
             {
                 var typeRefinement =
                     new InlineFragmentNode(
@@ -313,9 +314,11 @@ lookup is null
                 index = indexBuilder;
 
                 operationBuilder.SetSelectionSet(selectionSetWithTypeRefinement);
+
+                isAbstractLookup = true;
             }
 
-            operationBuilder.SetLookup(lookup, requirementKey);
+            operationBuilder.SetLookup(lookup, isAbstractLookup, requirementKey);
         }
 
         (var definition, index, var source) = operationBuilder.Build(index);
@@ -686,7 +689,32 @@ private void PlanFieldWithRequirement(
             requirements = requirements.Add(argumentRequirementKey, operationRequirement);
         }
 
-        operationBuilder.SetLookup(workItem.Lookup, requirementKey);
+        var isAbstractLookup = false;
+        if (_schema.Types.TryGetType(lookup.FieldType, out var lookupFieldType)
+            && lookupFieldType != selectionSetStub.Type
+            && !selectionSetNode.Selections.All(s => s is InlineFragmentNode inlineFragment
+                && inlineFragment.TypeCondition?.Name.Value == selectionSetStub.Type.Name))
+        {
+            var typeRefinement =
+                new InlineFragmentNode(
+                    null,
+                    new NamedTypeNode(selectionSetStub.Type.Name),
+                    [],
+                    selectionSetNode);
+            var selectionSetWithTypeRefinement = new SelectionSetNode(null, [typeRefinement]);
+
+            var indexBuilder = index.ToBuilder();
+
+            indexBuilder.Register(selectionSetNode, selectionSetWithTypeRefinement);
+
+            index = indexBuilder;
+
+            operationBuilder.SetSelectionSet(selectionSetWithTypeRefinement);
+
+            isAbstractLookup = true;
+        }
+
+        operationBuilder.SetLookup(workItem.Lookup, isAbstractLookup, requirementKey);
 
         var (definition, _, source) = operationBuilder.Build(index);