FieldsOnCorrectTypeRule: improve type coverage (#2404)

Author: IvanGoncharov

src/polyfills/arrayFrom.js

@@ -2,6 +2,8 @@
 
 import { SYMBOL_ITERATOR } from './symbols';
 
+declare function arrayFrom<T>(arrayLike: Iterable<T>): Array<T>;
+// eslint-disable-next-line no-redeclare
 declare function arrayFrom<T: mixed>(
   arrayLike: mixed,
   mapFn?: (elem: mixed, index: number) => T,

src/validation/rules/FieldsOnCorrectTypeRule.js

@@ -13,6 +13,8 @@ import { type ASTVisitor } from '../../language/visitor';
 import { type GraphQLSchema } from '../../type/schema';
 import {
   type GraphQLOutputType,
+  type GraphQLObjectType,
+  type GraphQLInterfaceType,
   isObjectType,
   isInterfaceType,
   isAbstractType,
@@ -79,7 +81,9 @@ function getSuggestedTypeNames(
     return [];
   }
 
-  const suggestedTypes = new Set();
+  const suggestedTypes: Set<
+    GraphQLObjectType | GraphQLInterfaceType,
+  > = new Set();
   const usageCount = Object.create(null);
   for (const possibleType of schema.getPossibleTypes(type)) {
     if (!possibleType.getFields()[fieldName]) {
@@ -111,10 +115,10 @@ function getSuggestedTypeNames(
       }
 
       // Suggest super types first followed by subtypes
-      if (isAbstractType(typeA) && schema.isSubType(typeA, typeB)) {
+      if (isInterfaceType(typeA) && schema.isSubType(typeA, typeB)) {
         return -1;
       }
-      if (isAbstractType(typeB) && schema.isSubType(typeB, typeA)) {
+      if (isInterfaceType(typeB) && schema.isSubType(typeB, typeA)) {
         return 1;
       }