Merge list fields correctly (#6109)

* Merge list fields correctly

* Changesets

* Tests

Author: ardatan

.changeset/brown-beers-relax.md

@@ -0,0 +1,5 @@
+---
+"@graphql-tools/federation": patch
+---
+
+Show responses in debug logging with `DEBUG` env var

.changeset/red-balloons-cheer.md

@@ -0,0 +1,5 @@
+---
+"@graphql-tools/delegate": patch
+---
+
+Merge list fields correctly

.changeset/tall-icons-poke.md

@@ -0,0 +1,5 @@
+---
+"@graphql-tools/stitch": patch
+---
+
+Exclude fields with `__typename` while extracting missing fields for the type merging

packages/delegate/src/mergeFields.ts

@@ -145,7 +145,17 @@ function handleResolverResult(
     const sourcePropValue = resolverResult[responseKey];
     if (sourcePropValue != null || existingPropValue == null) {
       if (existingPropValue != null && typeof existingPropValue === 'object') {
-        object[responseKey] = mergeDeep([existingPropValue, sourcePropValue]);
+        if (
+          Array.isArray(existingPropValue) &&
+          Array.isArray(sourcePropValue) &&
+          existingPropValue.length === sourcePropValue.length
+        ) {
+          object[responseKey] = existingPropValue.map((existingElement, index) =>
+            mergeDeep([existingElement, sourcePropValue[index]]),
+          );
+        } else {
+          object[responseKey] = mergeDeep([existingPropValue, sourcePropValue]);
+        }
       } else {
         object[responseKey] = sourcePropValue;
       }

packages/federation/src/supergraph.ts

@@ -692,12 +692,14 @@ export function getSubschemasFromSupergraphSdl({
     let executor: Executor = onExecutor({ subgraphName, endpoint, subgraphSchema: schema });
     if (globalThis.process?.env?.['DEBUG']) {
       const origExecutor = executor;
-      executor = function debugExecutor(execReq) {
+      executor = async function debugExecutor(execReq) {
         console.log(`Executing ${subgraphName} with args:`, {
           document: print(execReq.document),
-          variables: execReq.variables,
+          variables: JSON.stringify(execReq.variables, null, 2),
         });
-        return origExecutor(execReq);
+        const res = await origExecutor(execReq);
+        console.log(`Response from ${subgraphName}:`, JSON.stringify(res, null, 2));
+        return res;
       };
     }
     subschemaMap.set(subgraphName, {

packages/federation/test/.gitignore

@@ -0,0 +1 @@
+ignored-hidden

packages/stitch/src/getFieldsNotInSubschema.ts

@@ -82,8 +82,13 @@ export function extractUnavailableFields(field: GraphQLField<any, any>, fieldNod
     }
     const subFields = fieldType.getFields();
     const unavailableSelections: SelectionNode[] = [];
+    let hasTypeName = false;
     for (const selection of fieldNode.selectionSet.selections) {
       if (selection.kind === Kind.FIELD) {
+        if (selection.name.value === '__typename') {
+          hasTypeName = true;
+          continue;
+        }
         const selectionField = subFields[selection.name.value];
         if (!selectionField) {
           unavailableSelections.push(selection);
@@ -103,6 +108,15 @@ export function extractUnavailableFields(field: GraphQLField<any, any>, fieldNod
         // TODO: Support for inline fragments
       }
     }
+    if (unavailableSelections.length && hasTypeName) {
+      unavailableSelections.unshift({
+        kind: Kind.FIELD,
+        name: {
+          kind: Kind.NAME,
+          value: '__typename',
+        },
+      });
+    }
     return unavailableSelections;
   }
   return [];

packages/stitch/tests/extractUnavailableFields.test.ts

@@ -0,0 +1,112 @@
+import { getOperationAST, isObjectType, Kind, parse, print, SelectionSetNode } from 'graphql';
+import { makeExecutableSchema } from '@graphql-tools/schema';
+import { stripWhitespaces } from '../../merge/tests/utils';
+import { extractUnavailableFields } from '../src/getFieldsNotInSubschema';
+
+describe('extractUnavailableFields', () => {
+  it('should extract correct fields', () => {
+    const schema = makeExecutableSchema({
+      typeDefs: /* GraphQL */ `
+        type Query {
+          user: User
+        }
+        type User {
+          id: ID!
+          name: String!
+        }
+      `,
+    });
+    const userQuery = /* GraphQL */ `
+      query {
+        user {
+          id
+          name
+          email
+          friends {
+            id
+            name
+            email
+          }
+        }
+      }
+    `;
+    const userQueryDoc = parse(userQuery, { noLocation: true });
+    const operationAst = getOperationAST(userQueryDoc, null);
+    if (!operationAst) {
+      throw new Error('Operation AST not found');
+    }
+    const selectionSet = operationAst.selectionSet;
+    const userSelection = selectionSet.selections[0];
+    if (userSelection.kind !== 'Field') {
+      throw new Error('User selection not found');
+    }
+    const queryType = schema.getType('Query');
+    if (!isObjectType(queryType)) {
+      throw new Error('Query type not found');
+    }
+    const userField = queryType.getFields()['user'];
+    if (!userField) {
+      throw new Error('User field not found');
+    }
+    const unavailableFields = extractUnavailableFields(userField, userSelection);
+    const extractedSelectionSet: SelectionSetNode = {
+      kind: Kind.SELECTION_SET,
+      selections: unavailableFields,
+    };
+    expect(stripWhitespaces(print(extractedSelectionSet))).toBe(
+      `{ email friends { id name email } }`,
+    );
+  });
+  it('excludes the fields only with __typename', () => {
+    const schema = makeExecutableSchema({
+      typeDefs: /* GraphQL */ `
+        type Query {
+          user: User
+        }
+        type User {
+          id: ID!
+          name: String!
+          friends: [User]
+        }
+      `,
+    });
+    const userQuery = /* GraphQL */ `
+      query {
+        user {
+          __typename
+          id
+          name
+          friends {
+            __typename
+            id
+            name
+          }
+        }
+      }
+    `;
+    const userQueryDoc = parse(userQuery, { noLocation: true });
+    const operationAst = getOperationAST(userQueryDoc, null);
+    if (!operationAst) {
+      throw new Error('Operation AST not found');
+    }
+    const selectionSet = operationAst.selectionSet;
+    const userSelection = selectionSet.selections[0];
+    if (userSelection.kind !== 'Field') {
+      throw new Error('User selection not found');
+    }
+    const queryType = schema.getType('Query');
+    if (!isObjectType(queryType)) {
+      throw new Error('Query type not found');
+    }
+    const userField = queryType.getFields()['user'];
+    if (!userField) {
+      throw new Error('User field not found');
+    }
+    const unavailableFields = extractUnavailableFields(userField, userSelection);
+    const extractedSelectionSet: SelectionSetNode = {
+      kind: Kind.SELECTION_SET,
+      selections: unavailableFields,
+    };
+    expect(stripWhitespaces(print(extractedSelectionSet))).toBe('');
+  });
+});