Federation: Add tests with @defer (#6278)

* Federation: Add tests with `@defer`

* Fixes

.changeset/eleven-plums-tell.md

@@ -0,0 +1,7 @@
+---
+'@graphql-tools/delegate': patch
+'@graphql-tools/stitch': patch
+'@graphql-tools/utils': patch
+---
+
+Handle `@defer`

.changeset/nine-mayflies-retire.md

@@ -0,0 +1,5 @@
+---
+'@graphql-tools/federation': patch
+---
+
+Exclude `@defer` in the subgraph requests

packages/delegate/src/prepareGatewayDocument.ts

@@ -222,6 +222,8 @@ function visitSelectionSet(
           if (possibleTypes.length === 0) {
             newSelections.add(selection);
           }
+        } else {
+          newSelections.add(selection);
         }
       } else if (selection.kind === Kind.FRAGMENT_SPREAD) {
         const fragmentName = selection.name.value;

packages/federation/src/supergraph.ts

@@ -872,6 +872,12 @@ export function getStitchingOptionsFromSupergraphSdl(
               document: visit(
                 request.document,
                 visitWithTypeInfo(typeInfo, {
+                  [Kind.DIRECTIVE](node) {
+                    if (node.name.value === 'defer') {
+                      // @defer is not available for the communication between the gw and subgraph
+                      return null;
+                    }
+                  },
                   // To avoid resolving unresolvable interface fields
                   [Kind.FIELD](node) {
                     if (node.name.value !== '__typename') {

packages/federation/test/__snapshots__/defer.test.ts.snap

@@ -0,0 +1,256 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`Defer defers the nested fields: defer-nested-fields 1`] = `
+[
+  {
+    "data": {
+      "users": [
+        {
+          "id": "1",
+          "name": "Ada Lovelace",
+        },
+        {
+          "id": "2",
+          "name": "Alan Turing",
+        },
+      ],
+    },
+    "hasNext": true,
+  },
+  {
+    "hasNext": true,
+    "incremental": [
+      {
+        "data": {
+          "posts": [
+            {
+              "author": {
+                "id": "1",
+                "posts": [
+                  {
+                    "id": "1",
+                    "title": "Hello, World!",
+                  },
+                ],
+              },
+              "id": "1",
+              "title": "Hello, World!",
+            },
+            {
+              "author": {
+                "id": "2",
+                "posts": [
+                  {
+                    "id": "2",
+                    "title": "My Story",
+                  },
+                ],
+              },
+              "id": "2",
+              "title": "My Story",
+            },
+          ],
+        },
+        "path": [],
+      },
+      {
+        "data": {
+          "name": "Ada Lovelace",
+        },
+        "path": [
+          "posts",
+          0,
+          "author",
+        ],
+      },
+      {
+        "data": {
+          "name": "Alan Turing",
+        },
+        "path": [
+          "posts",
+          1,
+          "author",
+        ],
+      },
+    ],
+  },
+  {
+    "hasNext": true,
+    "incremental": [
+      {
+        "data": {
+          "posts": [
+            {
+              "author": {
+                "id": "1",
+              },
+              "id": "1",
+            },
+          ],
+        },
+        "path": [
+          "users",
+          0,
+        ],
+      },
+      {
+        "data": {
+          "posts": [
+            {
+              "author": {
+                "id": "2",
+              },
+              "id": "2",
+            },
+          ],
+        },
+        "path": [
+          "users",
+          1,
+        ],
+      },
+    ],
+  },
+  {
+    "hasNext": false,
+    "incremental": [
+      {
+        "data": {
+          "title": "Hello, World!",
+        },
+        "path": [
+          "users",
+          0,
+          "posts",
+          0,
+        ],
+      },
+      {
+        "data": {
+          "title": "My Story",
+        },
+        "path": [
+          "users",
+          1,
+          "posts",
+          0,
+        ],
+      },
+      {
+        "data": {
+          "name": "Ada Lovelace",
+        },
+        "path": [
+          "users",
+          0,
+          "posts",
+          0,
+          "author",
+        ],
+      },
+      {
+        "data": {
+          "name": "Alan Turing",
+        },
+        "path": [
+          "users",
+          1,
+          "posts",
+          0,
+          "author",
+        ],
+      },
+    ],
+  },
+]
+`;
+
+exports[`Defer defers the root fields: defer-root-fields 1`] = `
+[
+  {
+    "data": {},
+    "hasNext": true,
+  },
+  {
+    "hasNext": true,
+    "incremental": [
+      {
+        "data": {
+          "users": [
+            {
+              "id": "1",
+              "name": "Ada Lovelace",
+              "posts": [
+                {
+                  "author": {
+                    "id": "1",
+                    "name": "Ada Lovelace",
+                  },
+                  "id": "1",
+                  "title": "Hello, World!",
+                },
+              ],
+            },
+            {
+              "id": "2",
+              "name": "Alan Turing",
+              "posts": [
+                {
+                  "author": {
+                    "id": "2",
+                    "name": "Alan Turing",
+                  },
+                  "id": "2",
+                  "title": "My Story",
+                },
+              ],
+            },
+          ],
+        },
+        "path": [],
+      },
+    ],
+  },
+  {
+    "hasNext": false,
+    "incremental": [
+      {
+        "data": {
+          "posts": [
+            {
+              "author": {
+                "id": "1",
+                "name": "Ada Lovelace",
+                "posts": [
+                  {
+                    "id": "1",
+                    "title": "Hello, World!",
+                  },
+                ],
+              },
+              "id": "1",
+              "title": "Hello, World!",
+            },
+            {
+              "author": {
+                "id": "2",
+                "name": "Alan Turing",
+                "posts": [
+                  {
+                    "id": "2",
+                    "title": "My Story",
+                  },
+                ],
+              },
+              "id": "2",
+              "title": "My Story",
+            },
+          ],
+        },
+        "path": [],
+      },
+    ],
+  },
+]
+`;