Showcase issue without unions

src/HotChocolate/Fusion/test/Core.Tests/DemoIntegrationTests.cs

@@ -16,6 +16,79 @@ public class DemoIntegrationTests(ITestOutputHelper output)
 {
     private readonly Func<ICompositionLog> _logFactory = () => new TestCompositionLog(output);
 
+    [Fact]
+    public async Task Test()
+    {
+        // arrange
+        var subgraphA = await TestSubgraph.CreateAsync(
+            """
+            interface Node {
+              id: ID!
+            }
+
+            type Query {
+              productsA: [Product]
+              productsB: [Product]
+              node(id: ID!): Node
+              nodes(ids: [ID!]!): [Node]!
+            }
+
+            type Product implements Node {
+              id: ID!
+              name: String!
+            }
+            """);
+
+        var subgraphB = await TestSubgraph.CreateAsync(
+            """
+            interface Node {
+              id: ID!
+            }
+
+            type Query {
+              node(id: ID!): Node
+              nodes(ids: [ID!]!): [Node]!
+            }
+
+            type Product implements Node {
+              id: ID!
+              price: Float!
+              reviewCount: Int!
+            }
+            """);
+
+        using var subgraphs = new TestSubgraphCollection(output, [subgraphA, subgraphB]);
+        var executor = await subgraphs.GetExecutorAsync();
+        var request = Parse("""
+                      query {
+                        productsA {
+                          id
+                          name
+                          price
+                          reviewCount
+                        }
+                        productsB {
+                          id
+                          name
+                          price
+                          reviewCount
+                        }
+                      }
+                      """);
+
+        // act
+        var result = await executor.ExecuteAsync(
+            OperationRequestBuilder
+                .New()
+                .SetDocument(request)
+                .Build());
+
+        // assert
+        var snapshot = new Snapshot();
+        CollectSnapshotData(snapshot, request, result);
+        await snapshot.MatchMarkdownAsync();
+    }
+
     [Fact]
     public async Task Authors_And_Reviews_AutoCompose()
     {

src/HotChocolate/Fusion/test/Core.Tests/__snapshots__/DemoIntegrationTests.Test.md

@@ -0,0 +1,191 @@
+# Test
+
+## Result
+
+```json
+{
+  "errors": [
+    {
+      "message": "Cannot return null for non-nullable field.",
+      "locations": [
+        {
+          "line": 11,
+          "column": 5
+        }
+      ],
+      "path": [
+        "productsB",
+        2,
+        "price"
+      ],
+      "extensions": {
+        "code": "HC0018"
+      }
+    },
+    {
+      "message": "Cannot return null for non-nullable field.",
+      "locations": [
+        {
+          "line": 11,
+          "column": 5
+        }
+      ],
+      "path": [
+        "productsB",
+        1,
+        "price"
+      ],
+      "extensions": {
+        "code": "HC0018"
+      }
+    },
+    {
+      "message": "Cannot return null for non-nullable field.",
+      "locations": [
+        {
+          "line": 11,
+          "column": 5
+        }
+      ],
+      "path": [
+        "productsB",
+        0,
+        "price"
+      ],
+      "extensions": {
+        "code": "HC0018"
+      }
+    }
+  ],
+  "data": {
+    "productsA": [
+      {
+        "id": "1",
+        "name": "string",
+        "price": 123.456,
+        "reviewCount": 123
+      },
+      {
+        "id": "2",
+        "name": "string",
+        "price": 123.456,
+        "reviewCount": 123
+      },
+      {
+        "id": "3",
+        "name": "string",
+        "price": 123.456,
+        "reviewCount": 123
+      }
+    ],
+    "productsB": [
+      null,
+      null,
+      null
+    ]
+  }
+}
+```
+
+## Request
+
+```graphql
+{
+  productsA {
+    id
+    name
+    price
+    reviewCount
+  }
+  productsB {
+    id
+    name
+    price
+    reviewCount
+  }
+}
+```
+
+## QueryPlan Hash
+
+```text
+57DE21D1B552226339A985FBFA65E0DA2E33703C
+```
+
+## QueryPlan
+
+```json
+{
+  "document": "{ productsA { id name price reviewCount } productsB { id name price reviewCount } }",
+  "rootNode": {
+    "type": "Sequence",
+    "nodes": [
+      {
+        "type": "Resolve",
+        "subgraph": "Subgraph_1",
+        "document": "query fetch_productsA_productsB_1 { productsA { id name __fusion_exports__1: id } productsB { id name __fusion_exports__2: id } }",
+        "selectionSetId": 0,
+        "provides": [
+          {
+            "variable": "__fusion_exports__1"
+          },
+          {
+            "variable": "__fusion_exports__2"
+          }
+        ]
+      },
+      {
+        "type": "Compose",
+        "selectionSetIds": [
+          0
+        ]
+      },
+      {
+        "type": "Parallel",
+        "nodes": [
+          {
+            "type": "ResolveByKeyBatch",
+            "subgraph": "Subgraph_2",
+            "document": "query fetch_productsA_productsB_2($__fusion_exports__1: [ID!]!) { nodes(ids: $__fusion_exports__1) { ... on Product { price reviewCount __fusion_exports__1: id } } }",
+            "selectionSetId": 1,
+            "path": [
+              "nodes"
+            ],
+            "requires": [
+              {
+                "variable": "__fusion_exports__1"
+              }
+            ]
+          },
+          {
+            "type": "ResolveByKeyBatch",
+            "subgraph": "Subgraph_2",
+            "document": "query fetch_productsA_productsB_3($__fusion_exports__2: [ID!]!) { nodes(ids: $__fusion_exports__2) { ... on Product { price reviewCount __fusion_exports__2: id } } }",
+            "selectionSetId": 2,
+            "path": [
+              "nodes"
+            ],
+            "requires": [
+              {
+                "variable": "__fusion_exports__2"
+              }
+            ]
+          }
+        ]
+      },
+      {
+        "type": "Compose",
+        "selectionSetIds": [
+          1,
+          2
+        ]
+      }
+    ]
+  },
+  "state": {
+    "__fusion_exports__1": "Product_id",
+    "__fusion_exports__2": "Product_id"
+  }
+}
+```
+