fix(forms): improve error message for invalid value accessors

improve error message for invalid value accessors when accessor is not provided as array
angular · Feb 24, 2022 · c104e66 · c104e66
1 parent bad5096
commit c104e66
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Showing 2 changed files with 10 additions and 5 deletions.
diff --git a/packages/forms/src/directives/shared.ts b/packages/forms/src/directives/shared.ts
@@ -272,16 +272,18 @@ function _noControlError(dir: NgControl) {
   return _throwError(dir, 'There is no FormControl instance attached to form control element with');
 }
 
-function _throwError(dir: AbstractControlDirective, message: string): void {
+function _throwError(dir: AbstractControlDirective, message: string, extraMessage?: string): void {
   let messageEnd: string;
   if (dir.path!.length > 1) {
     messageEnd = `path: '${dir.path!.join(' -> ')}'`;
   } else if (dir.path![0]) {
     messageEnd = `name: '${dir.path}'`;
   } else {
-    messageEnd = 'unspecified name attribute';
+    messageEnd = 'unspecified name attribute.';
   }
-  throw new Error(`${message} ${messageEnd}`);
+
+  extraMessage = extraMessage ? '\n' + extraMessage : '';
+  throw new Error(`${message} ${messageEnd}${extraMessage}`);
 }
 
 export function isPropertyUpdated(changes: {[key: string]: any}, viewModel: any): boolean {
@@ -315,7 +317,9 @@ export function selectValueAccessor(
   if (!valueAccessors) return null;
 
   if (!Array.isArray(valueAccessors) && (typeof ngDevMode === 'undefined' || ngDevMode))
-    _throwError(dir, 'Value accessor was not provided as an array for form control with');
+    _throwError(
+        dir, 'Value accessor was not provided as an array for form control with',
+        'Please make sure that the `NG_VALUE_ACCESSOR` token is configured as a multi provider (with the `multi: true` property).');
 
   let defaultAccessor: ControlValueAccessor|undefined = undefined;
   let builtinAccessor: ControlValueAccessor|undefined = undefined;

diff --git a/packages/forms/test/directives_spec.ts b/packages/forms/test/directives_spec.ts
@@ -11,6 +11,7 @@ import {fakeAsync, flushMicrotasks, tick} from '@angular/core/testing';
 import {AbstractControl, CheckboxControlValueAccessor, ControlValueAccessor, DefaultValueAccessor, FormArray, FormArrayName, FormControl, FormControlDirective, FormControlName, FormGroup, FormGroupDirective, FormGroupName, NgControl, NgForm, NgModel, NgModelGroup, SelectControlValueAccessor, SelectMultipleControlValueAccessor, ValidationErrors, Validator, Validators} from '@angular/forms';
 import {selectValueAccessor} from '@angular/forms/src/directives/shared';
 import {composeValidators} from '@angular/forms/src/validators';
+
 import {asyncValidator} from './util';
 
 class DummyControlValueAccessor implements ControlValueAccessor {
@@ -53,7 +54,7 @@ class CustomValidatorDirective implements Validator {
         it('should throw when accessor is not provided as array', () => {
           expect(() => selectValueAccessor(dir, {} as any[]))
               .toThrowError(
-                  `Value accessor was not provided as an array for form control with unspecified name attribute`);
+                  'Value accessor was not provided as an array for form control with unspecified name attribute.\nPlease make sure that the `NG_VALUE_ACCESSOR` token is configured as a multi provider (with the `multi: true` property).');
         });
 
         it('should return the default value accessor when no other provided', () => {