feat(gatsby): allow referencing derived types in schema customization

packages/gatsby/src/schema/__tests__/build-schema.js

@@ -36,6 +36,7 @@ jest.mock(`gatsby-cli/lib/reporter`, () => {
     info: jest.fn(),
     warn: jest.fn(),
     error: jest.fn(),
+    panic: jest.fn(console.error),
     activityTimer: () => {
       return {
         start: jest.fn(),
@@ -1395,6 +1396,68 @@ describe(`Build schema`, () => {
         }"
       `)
     })
+
+    it(`Can reference derived types when merging types`, async () => {
+      createTypes(gql`
+        # create initial type composer
+        type TypeCreatedBySourcePlugin implements Node {
+          id: ID!
+          someField: String
+        }
+      `)
+      createTypes([
+        buildInterfaceType({
+          name: `SharedInterface`,
+          fields: {
+            id: `ID!`,
+            child_items: {
+              type: `[SharedInterface]`,
+              args: {
+                // referencing derived type
+                sort: `SharedInterfaceSortInput`,
+              },
+            },
+          },
+          interfaces: [`Node`],
+        }),
+        buildObjectType({
+          name: `TypeCreatedBySourcePlugin`,
+          fields: {
+            id: `ID!`,
+            child_items: {
+              type: `[SharedInterface]`,
+              args: {
+                sort: `SharedInterfaceSortInput`,
+              },
+              resolve: (_, args) => [],
+            },
+          },
+          interfaces: [`Node`, `SharedInterface`],
+        }),
+      ])
+
+      // implicit assertion is that building schema doesn't throw in the process
+      const schema = await buildSchema()
+      expect(printType(schema.getType(`TypeCreatedBySourcePlugin`)))
+        .toMatchInlineSnapshot(`
+        "type TypeCreatedBySourcePlugin implements Node & SharedInterface {
+          id: ID!
+          someField: String
+          child_items(sort: SharedInterfaceSortInput): [SharedInterface]
+          parent: Node
+          children: [Node!]!
+          internal: Internal!
+        }"
+      `)
+
+      expect(printType(schema.getType(`SharedInterfaceSortInput`)))
+        .toMatchInlineSnapshot(`
+        "input SharedInterfaceSortInput {
+          fields: [SharedInterfaceFieldsEnum]
+          order: [SortOrderEnum] = [ASC]
+        }"
+      `)
+    })
   })
 
   it(`allows renaming and merging nested types`, async () => {

packages/gatsby/src/schema/schema.js

@@ -143,21 +143,6 @@ const updateSchemaComposer = async ({
     parentSpan: parentSpan,
   })
   activity.start()
-  if (!process.env.GATSBY_SKIP_WRITING_SCHEMA_TO_FILE) {
-    await printTypeDefinitions({
-      config: printConfig,
-      schemaComposer,
-      parentSpan: activity.span,
-    })
-    if (enginePrintConfig) {
-      // make sure to print schema that will be used when bundling graphql-engine
-      await printTypeDefinitions({
-        config: enginePrintConfig,
-        schemaComposer,
-        parentSpan: activity.span,
-      })
-    }
-  }
   await addSetFieldsOnGraphQLNodeTypeFields({
     schemaComposer,
     parentSpan: activity.span,
@@ -184,6 +169,21 @@ const updateSchemaComposer = async ({
   })
   await addCustomResolveFunctions({ schemaComposer, parentSpan: activity.span })
   attachTracingResolver({ schemaComposer, parentSpan: activity.span })
+  if (!process.env.GATSBY_SKIP_WRITING_SCHEMA_TO_FILE) {
+    await printTypeDefinitions({
+      config: printConfig,
+      schemaComposer,
+      parentSpan: activity.span,
+    })
+    if (enginePrintConfig) {
+      // make sure to print schema that will be used when bundling graphql-engine
+      await printTypeDefinitions({
+        config: enginePrintConfig,
+        schemaComposer,
+        parentSpan: activity.span,
+      })
+    }
+  }
   activity.end()
 }