fix(core): improve error msg for invalid KeyValueDiffer.diff arg (#15489)

Closes #15402

packages/core/src/change_detection/differs/default_iterable_differ.ts

@@ -157,7 +157,8 @@ export class DefaultIterableDiffer<V> implements IterableDiffer<V>, IterableChan
   diff(collection: NgIterable<V>): DefaultIterableDiffer<V> {
     if (collection == null) collection = [];
     if (!isListLikeIterable(collection)) {
-      throw new Error(`Error trying to diff '${collection}'`);
+      throw new Error(
+          `Error trying to diff '${stringify(collection)}'. Only arrays and iterables are allowed`);
     }
 
     if (this.check(collection)) {

packages/core/src/change_detection/differs/default_keyvalue_differ.ts

@@ -9,7 +9,6 @@
 import {looseIdentical, stringify} from '../../util';
 import {isJsObject} from '../change_detection_util';
 import {ChangeDetectorRef} from '../change_detector_ref';
-
 import {KeyValueChangeRecord, KeyValueChanges, KeyValueDiffer, KeyValueDifferFactory} from './keyvalue_differs';
 
 
@@ -82,7 +81,8 @@ export class DefaultKeyValueDiffer<K, V> implements KeyValueDiffer<K, V>, KeyVal
     if (!map) {
       map = new Map();
     } else if (!(map instanceof Map || isJsObject(map))) {
-      throw new Error(`Error trying to diff '${map}'`);
+      throw new Error(
+          `Error trying to diff '${stringify(map)}'. Only maps and objects are allowed`);
     }
 
     return this.check(map) ? this : null;

packages/core/test/change_detection/differs/default_iterable_differ_spec.ts

@@ -472,7 +472,7 @@ export function main() {
         });
 
         it('should throw when given an invalid collection', () => {
-          expect(() => differ.diff('invalid')).toThrowError('Error trying to diff \'invalid\'');
+          expect(() => differ.diff('invalid')).toThrowError(/Error trying to diff 'invalid'/);
         });
       });
     });

packages/core/test/change_detection/differs/default_keyvalue_differ_spec.ts

@@ -220,8 +220,7 @@ export function main() {
         });
 
         it('should throw when given an invalid collection', () => {
-          expect(() => differ.diff(<any>'invalid'))
-              .toThrowError('Error trying to diff \'invalid\'');
+          expect(() => differ.diff(<any>'invalid')).toThrowError(/Error trying to diff 'invalid'/);
         });
       });
     });