feat(forms): add equalsTo validator (#14052)

PR Close: #14052

modules/@angular/forms/src/validators.ts

@@ -12,7 +12,7 @@ import {toPromise} from 'rxjs/operator/toPromise';
 import {AsyncValidatorFn, Validator, ValidatorFn} from './directives/validators';
 import {StringMapWrapper} from './facade/collection';
 import {isPresent} from './facade/lang';
-import {AbstractControl} from './model';
+import {AbstractControl, FormControl, FormGroup} from './model';
 import {isPromise} from './private_import_core';
 
 function isEmptyInputValue(value: any): boolean {
@@ -63,6 +63,30 @@ const EMAIL_REGEXP =
  * @stable
  */
 export class Validators {
+  /**
+   * Validator that compares the value of the given FormControls
+   */
+  static equalsTo(...fieldPaths: string[]): ValidatorFn {
+    return function(control: FormControl): {[key: string]: any} {
+      if (fieldPaths.length < 1) {
+        throw new Error('You must compare to at least 1 other field');
+      }
+
+      for (let fieldName of fieldPaths) {
+        let field = (<FormGroup>control.parent).get(fieldName);
+        if (!field) {
+          throw new Error(
+              `Field: ${fieldName} undefined, are you sure that ${fieldName} exists in the group`);
+        }
+
+        if (field.value !== control.value) {
+          return {'equalsTo': {'unequalField': fieldName}};
+        }
+      }
+      return null;
+    };
+  }
+
   /**
    * Validator that requires controls to have a non-empty value.
    */

modules/@angular/forms/test/validators_spec.ts

@@ -8,7 +8,7 @@
 
 import {fakeAsync, tick} from '@angular/core/testing';
 import {describe, expect, it} from '@angular/core/testing/testing_internal';
-import {AbstractControl, FormArray, FormControl, Validators} from '@angular/forms';
+import {AbstractControl, FormArray, FormControl, FormGroup, Validators} from '@angular/forms';
 import {Observable} from 'rxjs/Observable';
 
 import {normalizeAsyncValidator} from '../src/directives/normalize_validator';
@@ -36,6 +36,44 @@ export function main() {
   }
 
   describe('Validators', () => {
+    describe('equalsTo', () => {
+      it('should not error when equal', () => {
+        let group = new FormGroup({f1: new FormControl('a'), f2: new FormControl('a')});
+        let validator = Validators.equalsTo('f2');
+        expect(validator(group.controls['f1'])).toBeNull();
+      });
+
+      it('should error when not equal', () => {
+        let group = new FormGroup({f1: new FormControl('a'), f2: new FormControl('b')});
+        let validator = Validators.equalsTo('f2');
+        expect(validator(group.controls['f1'])).toEqual({equalsTo: {unequalField: 'f2'}});
+      });
+
+      it('should throw if passed a form control', () => {
+        let validator = Validators.equalsTo('f1', 'f2');
+        // cast it to any so we don't get TS errors
+        expect(() => validator(<any>new FormGroup({f1: new FormControl('')}))).toThrow();
+      });
+
+      it('should throw if passed a form array', () => {
+        let validator = Validators.equalsTo('f1', 'f2');
+        // cast it to any so we don't get TS errors
+        expect(() => validator(<any>new FormArray([]))).toThrow();
+      });
+
+      it('should throw if not passed any field to compare', () => {
+        let validator = Validators.equalsTo();
+        expect(() => validator(new FormControl('a'))).toThrow();
+      });
+
+      it('should throw if field passed does not exist in the group', () => {
+        let group = new FormGroup({f1: new FormControl('a'), f2: new FormControl('b')});
+        let validator = Validators.equalsTo('f3', 'f4');
+        // cast it to any so we don't get TS errors
+        expect(() => validator(new FormControl('a'))).toThrow();
+      });
+    });
+
     describe('required', () => {
       it('should error on an empty string',
          () => { expect(Validators.required(new FormControl(''))).toEqual({'required': true}); });

tools/public_api_guard/forms/index.d.ts

@@ -543,6 +543,7 @@ export declare class Validators {
     static email(control: AbstractControl): {
         [key: string]: boolean;
     };
+    static equalsTo(...fieldPaths: string[]): ValidatorFn;
     static maxLength(maxLength: number): ValidatorFn;
     static minLength(minLength: number): ValidatorFn;
     static nullValidator(c: AbstractControl): {