Alternate solution to #868

federation-js/src/composition/compose.ts

@@ -48,7 +48,7 @@ import {
 import { validateSDL } from 'graphql/validation/validate';
 import { compositionRules } from './rules';
 import { printSupergraphSdl } from '../service/printSupergraphSdl';
-import { mapGetOrSet, mapValues } from '../utilities';
+import { mapGetOrSet, mapValues, filterMap } from '../utilities';
 
 const EmptyQueryDefinition = {
   kind: Kind.OBJECT_TYPE_DEFINITION,
@@ -677,11 +677,7 @@ export function addFederationMetadataToSchemaNodes({
   }
 
   for (const [typeName, fieldsToDirectivesMap] of typeNameToFieldDirectivesMap.entries()) {
-    // It's plausible we're dealing with an incomplete schema here which might not
-    // account for all the types we saw when inspecting SDL. In the case that a
-    // type is extended with no base definition anywhere, it won't exist in the schema.
-    const type = schema.getType(typeName) as GraphQLObjectType | undefined;
-    if (!type) continue;
+    const type = schema.getType(typeName) as GraphQLObjectType;
 
     for (const [
       fieldName,
@@ -766,14 +762,22 @@ export function composeServices(services: ServiceDefinition[]): CompositionResul
 
   schema = lexicographicSortSchema(schema);
 
+  // Now that we have a constructed schema, we can filter this map based on types
+  // that made it into the schema successfully. Types that didn't make it into the
+  // schema will have related composition errors.
+  const filteredTypeNameToFieldDirectivesMap = filterMap(
+    typeNameToFieldDirectivesMap,
+    (typeName) => !!schema.getType(typeName),
+  );
+
   addFederationMetadataToSchemaNodes({
     schema,
     typeToServiceMap,
     externalFields,
     keyDirectivesMap,
     valueTypes,
     directiveDefinitionsMap,
-    typeNameToFieldDirectivesMap,
+    typeNameToFieldDirectivesMap: filteredTypeNameToFieldDirectivesMap,
   });
 
   if (errors.length > 0) {

federation-js/src/utilities/filterMap.ts

@@ -0,0 +1,14 @@
+// Filter a Map object (not to be confused with .filter().map())
+export function filterMap<K, V>(
+  map: Map<K, V>,
+  filterFn: (k: K, v: V) => boolean,
+): Map<K, V> {
+  const filteredMap = new Map<K, V>();
+
+  for (const [key, value] of map.entries()) {
+    if (filterFn(key, value)) {
+      filteredMap.set(key, value);
+    }
+  }
+  return filteredMap;
+}

federation-js/src/utilities/index.ts

@@ -2,3 +2,4 @@ export { assert } from './assert';
 export { isNotNullOrUndefined } from './isNotNullOrUndefined';
 export { mapGetOrSet } from './mapGetOrSet';
 export { mapValues } from './mapValues';
+export { filterMap } from './filterMap';