fix(gateway): merge selection sets of @requires fields

packages/apollo-gateway/src/FieldSet.ts

@@ -10,6 +10,7 @@ import {
   GraphQLObjectType,
 } from 'graphql';
 import { getResponseName } from './utilities/graphql';
+import _ from 'lodash';
 
 export interface Field<
   TParent extends GraphQLCompositeType = GraphQLCompositeType
@@ -147,6 +148,38 @@ function mergeSelectionSets(fieldNodes: FieldNode[]): SelectionSetNode {
 
   return {
     kind: 'SelectionSet',
-    selections,
+    selections: mergeFieldNodeSelectionSets(selections),
   };
 }
+
+function mergeFieldNodeSelectionSets(
+  selectionNodes: SelectionNode[],
+): SelectionNode[] {
+  const [fieldNodes, fragmentNodes] = _(selectionNodes)
+    .partition(
+      (node: SelectionNode): node is FieldNode => node.kind === 'Field',
+    )
+    .value();
+
+  const [aliasedFieldNodes, nonAliasedFieldNodes] = _(fieldNodes)
+    .partition((node) => node.alias)
+    .value();
+
+  const mergedFieldNodes = _(nonAliasedFieldNodes)
+    .groupBy((node) => node.name.value)
+    .values()
+    .map((nodesWithSameName) => {
+      const node = nodesWithSameName[0];
+      if (node.selectionSet) {
+        node.selectionSet.selections = mergeFieldNodeSelectionSets(
+          nodesWithSameName.flatMap(
+            (node) => node.selectionSet?.selections || [],
+          ),
+        );
+      }
+      return node;
+    })
+    .value();
+
+  return [...mergedFieldNodes, ...aliasedFieldNodes, ...fragmentNodes];
+}

packages/apollo-gateway/src/__tests__/integration/complex-key.test.ts

@@ -168,7 +168,6 @@ it('works fetches data correctly with complex / nested @key fields', async () =>
                 organization {
                   id
                   __typename
-                  id
                 }
               }
             }