fix(stepper): unable to internationalize labels

Adds a provider that allows for labels inside the stepper to be internationalized.

src/lib/stepper/public_api.ts

@@ -11,4 +11,4 @@ export * from './step-label';
 export * from './stepper';
 export * from './stepper-button';
 export * from './step-header';
-
+export * from './stepper-intl';

src/lib/stepper/step-header.html

@@ -13,6 +13,6 @@
   <!-- It there is no label template, fall back to the text label. -->
   <div class="mat-step-text-label" *ngIf="_stringLabel()">{{label}}</div>
 
-  <div class="mat-step-optional" *ngIf="optional">Optional</div>
+  <div class="mat-step-optional" *ngIf="optional">{{_intl.optionalLabel}}</div>
 </div>
 

src/lib/stepper/step-header.ts

@@ -7,8 +7,17 @@
  */
 
 import {coerceBooleanProperty, coerceNumberProperty} from '@angular/cdk/coercion';
-import {Component, Input, ViewEncapsulation} from '@angular/core';
+import {
+  Component,
+  Input,
+  ViewEncapsulation,
+  ChangeDetectorRef,
+  OnDestroy,
+} from '@angular/core';
+import {MATERIAL_COMPATIBILITY_MODE} from '@angular/material/core';
 import {MatStepLabel} from './step-label';
+import {MatStepperIntl} from './stepper-intl';
+import {Subscription} from 'rxjs/Subscription';
 
 
 @Component({
@@ -23,7 +32,9 @@ import {MatStepLabel} from './step-label';
   encapsulation: ViewEncapsulation.None,
   preserveWhitespaces: false,
 })
-export class MatStepHeader {
+export class MatStepHeader implements OnDestroy {
+  private _intlSubscription: Subscription;
+
   /** Icon for the given step. */
   @Input() icon: string;
 
@@ -62,6 +73,14 @@ export class MatStepHeader {
   }
   private _optional: boolean;
 
+  constructor(public _intl: MatStepperIntl, changeDetectorRef: ChangeDetectorRef) {
+    this._intlSubscription = _intl.changes.subscribe(() => changeDetectorRef.markForCheck());
+  }
+
+  ngOnDestroy() {
+    this._intlSubscription.unsubscribe();
+  }
+
   /** Returns string label of given step if it is a text label. */
   _stringLabel(): string | null {
     return this.label instanceof MatStepLabel ? null : this.label;

src/lib/stepper/stepper-intl.ts

@@ -0,0 +1,24 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {Injectable} from '@angular/core';
+import {Subject} from 'rxjs/Subject';
+
+
+/** Stepper data that is required for internationalization. */
+@Injectable()
+export class MatStepperIntl {
+  /**
+   * Stream that emits whenever the labels here are changed. Use this to notify
+   * components if the labels have changed after initialization.
+   */
+  changes: Subject<void> = new Subject<void>();
+
+  /** Label that is rendered below optional steps. */
+  optionalLabel = 'Optional';
+}

src/lib/stepper/stepper-module.ts

@@ -17,6 +17,7 @@ import {MatStepHeader} from './step-header';
 import {MatStepLabel} from './step-label';
 import {MatHorizontalStepper, MatStep, MatStepper, MatVerticalStepper} from './stepper';
 import {MatStepperNext, MatStepperPrevious} from './stepper-button';
+import {MatStepperIntl} from './stepper-intl';
 
 
 @NgModule({
@@ -41,5 +42,6 @@ import {MatStepperNext, MatStepperPrevious} from './stepper-button';
   ],
   declarations: [MatHorizontalStepper, MatVerticalStepper, MatStep, MatStepLabel, MatStepper,
     MatStepperNext, MatStepperPrevious, MatStepHeader],
+  providers: [MatStepperIntl],
 })
 export class MatStepperModule {}

src/lib/stepper/stepper.md

@@ -7,8 +7,8 @@ that drives a stepped workflow. Material stepper extends the CDK stepper and has
 styling.
 
 ### Stepper variants
-There are two stepper components: `mat-horizontal-stepper` and `mat-vertical-stepper`. They 
-can be used the same way. The only difference is the orientation of stepper. 
+There are two stepper components: `mat-horizontal-stepper` and `mat-vertical-stepper`. They
+can be used the same way. The only difference is the orientation of stepper.
 `mat-horizontal-stepper` selector can be used to create a horizontal stepper, and
 `mat-vertical-stepper` can be used to create a vertical stepper. `mat-step` components need to be
 placed inside either one of the two stepper components.
@@ -26,7 +26,7 @@ If a step's label is only text, then the `label` attribute can be used.
 </mat-vertical-stepper>
 ```
 
-For more complex labels, add a template with the `matStepLabel` directive inside the 
+For more complex labels, add a template with the `matStepLabel` directive inside the
 `mat-step`.
 ```html
 <mat-vertical-stepper>
@@ -49,22 +49,22 @@ There are two button directives to support navigation between different steps:
       <button mat-button matStepperNext>Next</button>
     </div>
   </mat-step>
-</mat-horizontal-stepper>  
+</mat-horizontal-stepper>
 ```
 
 ### Linear stepper
 The `linear` attribute can be set on `mat-horizontal-stepper` and `mat-vertical-stepper` to create
 a linear stepper that requires the user to complete previous steps before proceeding
 to following steps. For each `mat-step`, the `stepControl` attribute can be set to the top level
-`AbstractControl` that is used to check the validity of the step. 
+`AbstractControl` that is used to check the validity of the step.
 
 There are two possible approaches. One is using a single form for stepper, and the other is
 using a different form for each step.
 
 #### Using a single form
 When using a single form for the stepper, `matStepperPrevious` and `matStepperNext` have to be
 set to `type="button"` in order to prevent submission of the form before all steps
-are completed. 
+are completed.
 
 ```html
 <form [formGroup]="formGroup">
@@ -83,7 +83,7 @@ are completed.
       </div>
     </mat-step>
     ...
-  </mat-horizontal-stepper> 
+  </mat-horizontal-stepper>
 </form>
 ```
 
@@ -106,11 +106,11 @@ are completed.
 
 #### Optional step
 If completion of a step in linear stepper is not required, then the `optional` attribute can be set
-on `mat-step`. 
+on `mat-step`.
 
 #### Editable step
 By default, steps are editable, which means users can return to previously completed steps and
-edit their responses. `editable="true"` can be set on `mat-step` to change the default. 
+edit their responses. `editable="true"` can be set on `mat-step` to change the default.
 
 #### Completed step
 By default, the `completed` attribute of a step returns `true` if the step is valid (in case of
@@ -124,11 +124,25 @@ this default `completed` behavior by setting the `completed` attribute as needed
 - <kbd>TAB</kbd>: Focuses the next tabbable element
 - <kbd>TAB</kbd>+<kbd>SHIFT</kbd>: Focuses the previous tabbable element
 
+### Localizing labels
+Labels used by the stepper are provided through `MatStepperIntl`. Localization of these messages
+can be done by providing a subclass with translated values in your application root module.
+
+```ts
+@NgModule({
+  imports: [MatStepperModule],
+  providers: [
+    {provide: MatStepperIntl, useClass: MyIntl},
+  ],
+})
+export class MyApp {}
+```
+
 ### Accessibility
 The stepper is treated as a tabbed view for accessibility purposes, so it is given
 `role="tablist"` by default. The header of step that can be clicked to select the step
 is given `role="tab"`, and the content that can be expanded upon selection is given
 `role="tabpanel"`. `aria-selected` attribute of step header and `aria-expanded` attribute of
 step content is automatically set based on step selection change.
 
-The stepper and each step should be given a meaningful label via `aria-label` or `aria-labelledby`.
+The stepper and each step should be given a meaningful label via `aria-label` or `aria-labelledby`.

src/lib/stepper/stepper.spec.ts

@@ -2,14 +2,14 @@ import {Directionality} from '@angular/cdk/bidi';
 import {ENTER, LEFT_ARROW, RIGHT_ARROW, SPACE} from '@angular/cdk/keycodes';
 import {dispatchKeyboardEvent} from '@angular/cdk/testing';
 import {Component, DebugElement} from '@angular/core';
-import {async, ComponentFixture, TestBed} from '@angular/core/testing';
+import {async, ComponentFixture, TestBed, inject} from '@angular/core/testing';
 import {FormControl, FormGroup, ReactiveFormsModule, Validators} from '@angular/forms';
 import {By} from '@angular/platform-browser';
 import {NoopAnimationsModule} from '@angular/platform-browser/animations';
 import {MatStepperModule} from './index';
 import {MatHorizontalStepper, MatStepper, MatVerticalStepper} from './stepper';
 import {MatStepperNext, MatStepperPrevious} from './stepper-button';
-
+import {MatStepperIntl} from './stepper-intl';
 
 const VALID_REGEX = /valid/;
 
@@ -96,6 +96,21 @@ describe('MatHorizontalStepper', () => {
     it('should set done icon if step is not editable and is completed', () => {
       assertCorrectStepIcon(fixture, false, 'done');
     });
+
+    it('should re-render when the i18n labels change',
+      inject([MatStepperIntl], (intl: MatStepperIntl) => {
+        const header = fixture.debugElement.queryAll(By.css('mat-step-header'))[2].nativeElement;
+        const optionalLabel = header.querySelector('.mat-step-optional');
+
+        expect(optionalLabel).toBeTruthy();
+        expect(optionalLabel.textContent).toBe('Optional');
+
+        intl.optionalLabel = 'Valgfri';
+        intl.changes.next();
+        fixture.detectChanges();
+
+        expect(optionalLabel.textContent).toBe('Valgfri');
+      }));
   });
 
   describe('RTL', () => {
@@ -684,7 +699,7 @@ function assertCorrectStepIcon(fixture: ComponentFixture<any>,
           <button mat-button matStepperNext>Next</button>
         </div>
       </mat-step>
-      <mat-step [label]="inputLabel">
+      <mat-step [label]="inputLabel" optional>
         Content 3
         <div>
           <button mat-button matStepperPrevious>Back</button>