[Fusion] Fix planning of nested fields under abstract node lookup

src/HotChocolate/Fusion/src/Fusion.Execution/Planning/Partitioners/SelectionSetByTypePartitioner.cs

@@ -2,7 +2,6 @@
 using System.Diagnostics.CodeAnalysis;
 using HotChocolate.Fusion.Types;
 using HotChocolate.Language;
-using HotChocolate.Language.Visitors;
 using HotChocolate.Types;
 
 namespace HotChocolate.Fusion.Planning.Partitioners;
@@ -145,42 +144,52 @@ private void AddSelectionsForConcreteType(
 
         if (cloneSelectionSets)
         {
-            var rewrittenSelections = new List<ISelectionNode>(selections.Count);
-
             foreach (var selection in selections)
             {
-                var rewrittenSelection = SyntaxRewriter.Create(
-                    node =>
-                    {
-                        if (node is SelectionSetNode selectionSetNode)
-                        {
-                            var newSelectionSet = new SelectionSetNode(selectionSetNode.Selections);
-
-                            // Since we're cloning the selection set,
-                            // we also need to keep track of the original
-                            // selection set the cloned one belongs to,
-                            // so we can later insert requirements in the original one.
-                            context.SelectionSetIndexBuilder.RegisterCloned(
-                                selectionSetNode,
-                                newSelectionSet);
-
-                            return newSelectionSet;
-                        }
-
-                        return node;
-                    }).Rewrite(selection)!;
-
-                rewrittenSelections.Add(rewrittenSelection);
+                typeSelections.Add(CloneSelection(selection, context.SelectionSetIndexBuilder));
             }
-
-            typeSelections.AddRange(rewrittenSelections);
         }
         else
         {
             typeSelections.AddRange(selections);
         }
     }
 
+    // Walks the selection top-down, cloning every nested SelectionSetNode so that
+    // each clone can be registered against its original in the index. We can't use
+    // the bottom-up SyntaxRewriter for this, because by the time it reaches an outer
+    // SelectionSetNode its children have already been replaced, leaving the rewriter
+    // with a freshly allocated node that isn't tracked in the index.
+    private static ISelectionNode CloneSelection(
+        ISelectionNode selection,
+        SelectionSetIndexBuilder indexBuilder)
+    {
+        return selection switch
+        {
+            FieldNode field when field.SelectionSet is not null
+                => field.WithSelectionSet(CloneSelectionSet(field.SelectionSet, indexBuilder)),
+            InlineFragmentNode fragment
+                => fragment.WithSelectionSet(CloneSelectionSet(fragment.SelectionSet, indexBuilder)),
+            _ => selection
+        };
+    }
+
+    private static SelectionSetNode CloneSelectionSet(
+        SelectionSetNode original,
+        SelectionSetIndexBuilder indexBuilder)
+    {
+        var clonedSelections = new ISelectionNode[original.Selections.Count];
+
+        for (var i = 0; i < original.Selections.Count; i++)
+        {
+            clonedSelections[i] = CloneSelection(original.Selections[i], indexBuilder);
+        }
+
+        var cloned = new SelectionSetNode(clonedSelections);
+        indexBuilder.RegisterCloned(original, cloned);
+        return cloned;
+    }
+
     private static List<ISelectionNode> GetSelectionsWithPath(
         Stack<InlineFragmentNode> fragmentPath,
         List<ISelectionNode> selections,

src/HotChocolate/Fusion/test/Fusion.AspNetCore.Tests/GlobalObjectIdentificationTests.cs

@@ -3,8 +3,6 @@
 
 namespace HotChocolate.Fusion;
 
-// TODO:
-// - Selections on interface, all types of interfaces are on same subgraph and there's only node lookup
 public class GlobalObjectIdentificationTests : FusionTestBase
 {
     [Fact]
@@ -1475,4 +1473,163 @@ ... on Discussion {
         // assert
         await MatchSnapshotAsync(gateway, request, result);
     }
+
+    [Fact]
+    public async Task Node_Field_Interface_Selection_All_Implementations_In_Same_Subgraph_Only_Node_Lookup()
+    {
+        // arrange
+        using var serverA = CreateSourceSchema(
+            "A",
+            """
+            type Query {
+              node(id: ID!): Node @lookup
+            }
+
+            interface Node {
+              id: ID!
+            }
+
+            interface IOrder {
+              id: ID!
+              name: String!
+            }
+
+            type Order1 implements Node & IOrder {
+              id: ID!
+              name: String!
+            }
+
+            type Order2 implements Node & IOrder {
+              id: ID!
+              name: String!
+            }
+            """);
+
+        using var gateway = await CreateCompositeSchemaAsync(
+        [
+            ("A", serverA)
+        ]);
+
+        // act
+        using var client = GraphQLHttpClient.Create(gateway.CreateClient());
+
+        var request = new OperationRequest(
+            """
+            {
+              # Order1:1
+              node(id: "T3JkZXIxOjE=") {
+                ... on IOrder {
+                  name
+                }
+              }
+            }
+            """);
+
+        using var result = await client.PostAsync(
+            request,
+            new Uri("http://localhost:5000/graphql"));
+
+        // assert
+        await MatchSnapshotAsync(gateway, request, result);
+    }
+
+    [Fact]
+    public async Task Node_Field_Interface_Selection_With_Nested_Field_From_Other_Subgraph()
+    {
+        // arrange
+        using var serverA = CreateSourceSchema(
+            "A",
+            """
+            type Query {
+              node(id: ID!): Node @lookup @shareable
+              order1ById(id: ID!): Order1 @lookup
+              order2ById(id: ID!): Order2 @lookup
+              orders: [IOrder!]!
+            }
+
+            interface Node {
+              id: ID!
+            }
+
+            interface IOrder {
+              id: ID!
+              name: String!
+              product: Product!
+            }
+
+            type Order1 implements Node & IOrder {
+              id: ID!
+              name: String!
+              product: Product!
+            }
+
+            type Order2 implements Node & IOrder {
+              id: ID!
+              name: String!
+              product: Product!
+            }
+
+            type Product {
+              id: ID! @shareable
+            }
+            """);
+
+        using var serverB = CreateSourceSchema(
+            "B",
+            """
+            type Query {
+              node(id: ID!): Node @lookup @shareable
+              products: [Product!]!
+              productById(id: ID!): Product @lookup @internal
+            }
+
+            interface Node {
+              id: ID!
+            }
+
+            type Product implements Node {
+              id: ID! @shareable
+              name: String!
+              comments: [Comment!]!
+            }
+
+            type Comment {
+              content: String!
+            }
+            """);
+
+        using var gateway = await CreateCompositeSchemaAsync(
+        [
+            ("A", serverA),
+            ("B", serverB)
+        ]);
+
+        // act
+        using var client = GraphQLHttpClient.Create(gateway.CreateClient());
+
+        var request = new OperationRequest(
+            """
+            {
+              # Order1:1
+              node(id: "T3JkZXIxOjE=") {
+                ... on IOrder {
+                  name
+                  product {
+                    name
+                    comments {
+                      content
+                    }
+                  }
+                }
+              }
+            }
+            """);
+
+        using var result = await client.PostAsync(
+            request,
+            new Uri("http://localhost:5000/graphql"));
+
+        // assert
+        await MatchSnapshotAsync(gateway, request, result);
+    }
 }

src/HotChocolate/Fusion/test/Fusion.AspNetCore.Tests/__snapshots__/GlobalObjectIdentificationTests.Node_Field_Interface_Selection_All_Implementations_In_Same_Subgraph_Only_Node_Lookup.yaml

@@ -0,0 +1,135 @@
+title: Node_Field_Interface_Selection_All_Implementations_In_Same_Subgraph_Only_Node_Lookup
+request:
+  document: |
+    {
+      node(id: "T3JkZXIxOjE=") {
+        ... on IOrder {
+          name
+        }
+      }
+    }
+response:
+  body: |
+    {
+      "data": {
+        "node": {
+          "name": "Order1: T3JkZXIxOjE="
+        }
+      }
+    }
+sourceSchemas:
+  - name: A
+    schema: |
+      schema {
+        query: Query
+      }
+
+      type Query {
+        node(id: ID!): Node @lookup
+      }
+
+      type Order1 implements Node & IOrder {
+        id: ID!
+        name: String!
+      }
+
+      type Order2 implements Node & IOrder {
+        id: ID!
+        name: String!
+      }
+
+      interface IOrder {
+        id: ID!
+        name: String!
+      }
+
+      interface Node {
+        id: ID!
+      }
+    interactions:
+      - request:
+          accept: application/graphql-response+json; charset=utf-8, application/json; charset=utf-8, application/jsonl; charset=utf-8, text/event-stream; charset=utf-8
+          document: |
+            query Op_a088b140_4 {
+              node(id: "T3JkZXIxOjE=") {
+                __typename
+                ... on Order1 {
+                  __typename
+                  name
+                }
+              }
+            }
+        response:
+          results:
+            - |
+              {
+                "data": {
+                  "node": {
+                    "__typename": "Order1",
+                    "name": "Order1: T3JkZXIxOjE="
+                  }
+                }
+              }
+operationPlan:
+  operation:
+    - document: |
+        {
+          node(id: "T3JkZXIxOjE=") {
+            __typename @fusion__requirement
+            ... on IOrder {
+              name
+            }
+          }
+        }
+      hash: a088b140315a0c889324bbc829bbc277
+      searchSpace: 1
+      expandedNodes: 1
+  nodes:
+    - id: 1
+      type: Node
+      idValue: "T3JkZXIxOjE="
+      responseName: node
+      branches:
+        - Order1: 4
+        - Order2: 3
+      fallback: 2
+    - id: 2
+      type: Operation
+      operation: |
+        query Op_a088b140_2 {
+          node(id: "T3JkZXIxOjE=") {
+            __typename
+          }
+        }
+      dependencies:
+        - id: 1
+    - id: 3
+      type: Operation
+      schema: A
+      operation: |
+        query Op_a088b140_3 {
+          node(id: "T3JkZXIxOjE=") {
+            __typename
+            ... on Order2 {
+              __typename
+              name
+            }
+          }
+        }
+      dependencies:
+        - id: 1
+    - id: 4
+      type: Operation
+      schema: A
+      operation: |
+        query Op_a088b140_4 {
+          node(id: "T3JkZXIxOjE=") {
+            __typename
+            ... on Order1 {
+              __typename
+              name
+            }
+          }
+        }
+      dependencies:
+        - id: 1