refactor: provide and use light-weight token for button-toggle group

goldens/size-test.yaml

@@ -2,3 +2,4 @@ material/list/nav-list: 130473
 material/radio/without-group: 121448
 material/menu/without-lazy-content: 210751
 material/datepicker/range-picker/without-form-field: 330101
+material/button-toggle/standalone: 119400

integration/size-test/material/button-toggle/BUILD.bazel

@@ -0,0 +1,7 @@
+load("//integration/size-test:index.bzl", "size_test")
+
+size_test(
+    name = "standalone",
+    file = "standalone.ts",
+    deps = ["//src/material/button-toggle"],
+)

integration/size-test/material/button-toggle/standalone.ts

@@ -0,0 +1,23 @@
+import {Component, NgModule} from '@angular/core';
+import {platformBrowser} from '@angular/platform-browser';
+import {MatButtonToggleModule} from '@angular/material/button-toggle';
+
+/**
+ * Basic component using a standalone `MatButtonToggle`. Other parts of the button-toggle
+ * module such as `MatButtonToggleGroup` are not used and should be tree-shaken away.
+ */
+@Component({
+  template: `
+    <mat-button-toggle>Center text</mat-button-toggle>
+  `,
+})
+export class TestComponent {}
+
+@NgModule({
+  imports: [MatButtonToggleModule],
+  declarations: [TestComponent],
+  bootstrap: [TestComponent],
+})
+export class AppModule {}
+
+platformBrowser().bootstrapModule(AppModule);

src/material/button-toggle/button-toggle.ts

@@ -61,7 +61,13 @@ export interface MatButtonToggleDefaultOptions {
 export const MAT_BUTTON_TOGGLE_DEFAULT_OPTIONS =
     new InjectionToken<MatButtonToggleDefaultOptions>('MAT_BUTTON_TOGGLE_DEFAULT_OPTIONS');
 
-
+/**
+ * Injection token that can be used to reference instances of `MatButtonToggleGroup`.
+ * It serves as alternative token to the actual `MatButtonToggleGroup` class which
+ * could cause unnecessary retention of the class and its component metadata.
+ */
+export const MAT_BUTTON_TOGGLE_GROUP =
+    new InjectionToken<MatButtonToggleGroup>('MatButtonToggleGroup');
 
 /**
  * Provider Expression that allows mat-button-toggle-group to register as a ControlValueAccessor.
@@ -89,7 +95,10 @@ export class MatButtonToggleChange {
 /** Exclusive selection button toggle group that behaves like a radio-button group. */
 @Directive({
   selector: 'mat-button-toggle-group',
-  providers: [MAT_BUTTON_TOGGLE_GROUP_VALUE_ACCESSOR],
+  providers: [
+    MAT_BUTTON_TOGGLE_GROUP_VALUE_ACCESSOR,
+    {provide: MAT_BUTTON_TOGGLE_GROUP, useExisting: MatButtonToggleGroup},
+  ],
   host: {
     'role': 'group',
     'class': 'mat-button-toggle-group',
@@ -476,7 +485,7 @@ export class MatButtonToggle extends _MatButtonToggleMixinBase implements OnInit
   @Output() readonly change: EventEmitter<MatButtonToggleChange> =
       new EventEmitter<MatButtonToggleChange>();
 
-  constructor(@Optional() toggleGroup: MatButtonToggleGroup,
+  constructor(@Optional() @Inject(MAT_BUTTON_TOGGLE_GROUP) toggleGroup: MatButtonToggleGroup,
               private _changeDetectorRef: ChangeDetectorRef,
               private _elementRef: ElementRef<HTMLElement>,
               private _focusMonitor: FocusMonitor,

tools/public_api_guard/material/button-toggle.d.ts

@@ -1,5 +1,7 @@
 export declare const MAT_BUTTON_TOGGLE_DEFAULT_OPTIONS: InjectionToken<MatButtonToggleDefaultOptions>;
 
+export declare const MAT_BUTTON_TOGGLE_GROUP: InjectionToken<MatButtonToggleGroup>;
+
 export declare const MAT_BUTTON_TOGGLE_GROUP_VALUE_ACCESSOR: any;
 
 export declare class MatButtonToggle extends _MatButtonToggleMixinBase implements OnInit, AfterViewInit, CanDisableRipple, OnDestroy {