Insert type refinement for abstract lookups

Author: tobias-tengler

src/HotChocolate/Fusion-vnext/src/Fusion.Execution.Types/Metadata/Lookup.cs

@@ -17,7 +17,7 @@ public sealed class Lookup : INeedsCompletion
     /// </summary>
     /// <param name="schemaName">The name of the source schema.</param>
     /// <param name="declaringTypeName">The name of the type that declares the field.</param>
-    /// <param name="name">The name of the lookup field.</param>
+    /// <param name="fieldName">The name of the lookup field.</param>
     /// <param name="arguments">The arguments that represent field requirements.</param>
     /// <param name="fields">The paths to the field that are required.</param>
     /// <exception cref="ArgumentException">
@@ -30,13 +30,13 @@ public sealed class Lookup : INeedsCompletion
     public Lookup(
         string schemaName,
         string declaringTypeName,
-        string name,
+        string fieldName,
         ImmutableArray<LookupArgument> arguments,
         ImmutableArray<IValueSelectionNode> fields)
     {
         ArgumentException.ThrowIfNullOrEmpty(schemaName);
         ArgumentException.ThrowIfNullOrEmpty(declaringTypeName);
-        ArgumentException.ThrowIfNullOrEmpty(name);
+        ArgumentException.ThrowIfNullOrEmpty(fieldName);
 
         if (arguments.Length == 0)
         {
@@ -50,7 +50,7 @@ public Lookup(
 
         _declaringTypeName = declaringTypeName;
         SchemaName = schemaName;
-        Name = name;
+        FieldName = fieldName;
         Arguments = arguments;
         Fields = fields;
     }
@@ -63,7 +63,12 @@ public Lookup(
     /// <summary>
     /// Gets the name of the lookup field.
     /// </summary>
-    public string Name { get; }
+    public string FieldName { get; }
+
+    /// <summary>
+    /// Get the name of lookup field type.
+    /// </summary>
+    public string FieldType => _declaringTypeName;
 
     /// <summary>
     /// Gets the arguments that represent field requirements.

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

@@ -76,7 +76,7 @@ public OperationDefinitionBuilder SetSelectionSet(SelectionSetNode selectionSet)
             }
 
             var lookupField = new FieldNode(
-                new NameNode(_lookup.Name),
+                new NameNode(_lookup.FieldName),
                 null,
                 [],
                 arguments,
@@ -87,7 +87,7 @@ public OperationDefinitionBuilder SetSelectionSet(SelectionSetNode selectionSet)
             var indexBuilder = index.ToBuilder();
             indexBuilder.Register(selectionSet);
             index = indexBuilder;
-            selectionPath = selectionPath.AppendField(_lookup.Name);
+            selectionPath = selectionPath.AppendField(_lookup.FieldName);
         }
 
         var definition = new OperationDefinitionNode(

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

@@ -295,6 +295,28 @@ 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.
+            if (_schema.Types.TryGetType(lookup.FieldType, out var lookupFieldType)
+                && lookupFieldType != workItem.SelectionSet.Type)
+            {
+                var typeRefinement =
+                    new InlineFragmentNode(
+                        null,
+                        new NamedTypeNode(workItem.SelectionSet.Type.Name),
+                        [],
+                        resolvable);
+                var selectionSetWithTypeRefinement = new SelectionSetNode(null, [typeRefinement]);
+
+                var indexBuilder = index.ToBuilder();
+
+                indexBuilder.Register(resolvable, selectionSetWithTypeRefinement);
+
+                index = indexBuilder;
+
+                operationBuilder.SetSelectionSet(selectionSetWithTypeRefinement);
+            }
+
             operationBuilder.SetLookup(lookup, requirementKey);
         }
 

src/HotChocolate/Fusion-vnext/test/Fusion.Execution.Tests/Planning/__snapshots__/OperationPlannerTests.Plan_Simple_Interface_Lookup.yaml

@@ -1,13 +1,13 @@
 operation:
   - document: >-
-      query GetTopProducts {
-        topProduct {
-          id
-          name
-          price
-          id @fusion__requirement
-        }
+    query GetTopProducts {
+      topProduct {
+        id
+        name
+        price
+        id @fusion__requirement
       }
+    }
     name: GetTopProducts
     hash: 123
 nodes:
@@ -27,7 +27,9 @@ nodes:
         $__fusion_1_id: ID!
       ) {
         node(id: $__fusion_1_id) {
-          price
+          ... on Product {
+            price
+          }
         }
       }
     source: $.node

src/HotChocolate/Fusion-vnext/test/Fusion.Execution.Tests/Planning/__snapshots__/OperationPlannerTests.Plan_Simple_Union_Lookup.yaml

@@ -1,13 +1,13 @@
 operation:
   - document: >-
-      query GetTopProducts {
-        topProduct {
-          id
-          name
-          price
-          id @fusion__requirement
-        }
+    query GetTopProducts {
+      topProduct {
+        id
+        name
+        price
+        id @fusion__requirement
       }
+    }
     name: GetTopProducts
     hash: 123
 nodes:
@@ -27,7 +27,9 @@ nodes:
         $__fusion_1_id: ID!
       ) {
         lookupUnionById(id: $__fusion_1_id) {
-          price
+          ... on Product {
+            price
+          }
         }
       }
     source: $.lookupUnionById