Allow to use @provide with interfaces

Author: vitramir

packages/apollo-federation/src/composition/compose.ts

@@ -131,7 +131,9 @@ export function buildMapsFromServiceList(serviceList: ServiceDefinition[]) {
     for (let definition of typeDefsWithoutExternalFields.definitions) {
       if (
         definition.kind === Kind.OBJECT_TYPE_DEFINITION ||
-        definition.kind === Kind.OBJECT_TYPE_EXTENSION
+        definition.kind === Kind.OBJECT_TYPE_EXTENSION ||
+        definition.kind === Kind.INTERFACE_TYPE_DEFINITION ||
+        definition.kind === Kind.INTERFACE_TYPE_EXTENSION
       ) {
         const typeName = definition.name.value;
 

packages/apollo-federation/src/composition/utils.ts

@@ -16,6 +16,7 @@ import {
   GraphQLError,
   GraphQLSchema,
   isObjectType,
+  isInterfaceType,
   GraphQLObjectType,
   getNamedType,
   GraphQLField,
@@ -219,7 +220,7 @@ export function findFieldsThatReturnType({
   schema: GraphQLSchema;
   typeToFind: GraphQLNamedType;
 }): GraphQLField<any, any>[] {
-  if (!isObjectType(typeToFind)) return [];
+  if (!isObjectType(typeToFind) && !isInterfaceType(typeToFind)) return [];
 
   const fieldsThatReturnType: GraphQLField<any, any>[] = [];
   const types = schema.getTypeMap();

packages/apollo-federation/src/composition/validate/postComposition/externalUnused.ts

@@ -62,29 +62,37 @@ export const externalUnused = (schema: GraphQLSchema) => {
               reviews: [Review]
             }
           */
-          const hasMatchingProvidesOnAnotherType = findFieldsThatReturnType({
-            schema,
-            typeToFind: parentType,
-          }).some(field =>
-            findDirectivesOnTypeOrField(field.astNode, 'provides').some(
-              directive => {
-                if (!directive.arguments) return false;
-                const selections =
-                  isStringValueNode(directive.arguments[0].value) &&
-                  parseSelections(directive.arguments[0].value.value);
-                // find the selections which are fields with names matching
-                // our external field name
-                return (
-                  selections &&
-                  selections.some(
-                    selection =>
-                      selection.kind === Kind.FIELD &&
-                      selection.name.value === externalFieldName,
-                  )
-                );
-              },
-            ),
-          );
+          const hasMatchingProvidesOnAnotherType = [
+            parentType,
+            ...parentType.getInterfaces(),
+          ]
+            .map(searchType =>
+              findFieldsThatReturnType({
+                schema,
+                typeToFind: searchType,
+              }),
+            )
+            .flat()
+            .some(field =>
+              findDirectivesOnTypeOrField(field.astNode, 'provides').some(
+                directive => {
+                  if (!directive.arguments) return false;
+                  const selections =
+                    isStringValueNode(directive.arguments[0].value) &&
+                    parseSelections(directive.arguments[0].value.value);
+                  // find the selections which are fields with names matching
+                  // our external field name
+                  return (
+                    selections &&
+                    selections.some(
+                      selection =>
+                        selection.kind === Kind.FIELD &&
+                        selection.name.value === externalFieldName,
+                    )
+                  );
+                },
+              ),
+            );
 
           if (hasMatchingProvidesOnAnotherType) continue;
 

packages/apollo-federation/src/composition/validate/postComposition/providesNotOnEntity.ts

@@ -1,6 +1,7 @@
 import {
   GraphQLSchema,
   isObjectType,
+  isInterfaceType,
   GraphQLError,
   isListType,
   isNonNullType,
@@ -47,7 +48,7 @@ export const providesNotOnEntity = (schema: GraphQLSchema) => {
 
       // field has a @provides directive on it
       if (field.federation && field.federation.provides) {
-        if (!isObjectType(baseType)) {
+        if (!isObjectType(baseType) && !isInterfaceType(baseType)) {
           errors.push(
             errorWithCode(
               'PROVIDES_NOT_ON_ENTITY',