refactor(cdk/private): set up private package and style loader

Creates a new `cdk/private` package in which we can put shared code that isn't meant to be public and creates a new style loader service that can be used to load structural styles for components.

Author: crisbeto

.ng-dev/commit-message.mts

@@ -31,6 +31,7 @@ export const commitMessage: CommitMessageConfig = {
     'cdk/overlay',
     'cdk/platform',
     'cdk/portal',
+    'cdk/private',
     'cdk/schematics',
     'cdk/scrolling',
     'cdk/stepper',

scripts/check-entry-point-setup.js

@@ -23,6 +23,7 @@ const packagesDir = join(__dirname, '../src');
  */
 const excludeGlobs = [
   'cdk/testing/private',
+  'cdk/private',
   '*/schematics/**',
   // The protractor testing entry-point is no longer publicly available,
   // but exists in the repository until it can be removed in g3.

src/cdk/config.bzl

@@ -26,6 +26,7 @@ CDK_ENTRYPOINTS = [
     "testing",
     "testing/testbed",
     "testing/selenium-webdriver",
+    "private",
 ]
 
 # List of all entry-point targets of the Angular Material package.

src/cdk/private/BUILD.bazel

@@ -0,0 +1,24 @@
+load("//tools:defaults.bzl", "markdown_to_html", "ng_module")
+
+package(default_visibility = ["//visibility:public"])
+
+ng_module(
+    name = "private",
+    srcs = glob(
+        ["**/*.ts"],
+        exclude = ["**/*.spec.ts"],
+    ),
+    deps = [
+        "@npm//@angular/core",
+    ],
+)
+
+markdown_to_html(
+    name = "overview",
+    srcs = [":private.md"],
+)
+
+filegroup(
+    name = "source-files",
+    srcs = glob(["**/*.ts"]),
+)

src/cdk/private/index.ts

@@ -0,0 +1,9 @@
+/**
+ * @license
+ * Copyright Google LLC 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
+ */
+
+export * from './public-api';

src/cdk/private/private.md

@@ -0,0 +1 @@
+Private utilities meant to be used only within the CDK and Material.

src/cdk/private/public-api.ts

@@ -0,0 +1,9 @@
+/**
+ * @license
+ * Copyright Google LLC 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
+ */
+
+export * from './style-loader';

src/cdk/private/style-loader.ts

@@ -0,0 +1,65 @@
+/**
+ * @license
+ * Copyright Google LLC 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 {
+  ApplicationRef,
+  ComponentRef,
+  createComponent,
+  EnvironmentInjector,
+  inject,
+  Injectable,
+  Type,
+} from '@angular/core';
+
+/** Apps in which we've loaded styles. */
+const appsWithLoaders = new WeakMap<
+  ApplicationRef,
+  {
+    /** Style loaders that have been added. */
+    loaders: Set<Type<unknown>>;
+
+    /** References to the instantiated loaders. */
+    refs: ComponentRef<unknown>[];
+  }
+>();
+
+/**
+ * Service that loads structural styles dynamically
+ * and ensures that they're only loaded once per app.
+ */
+@Injectable({providedIn: 'root'})
+export class _CdkPrivateStyleLoader {
+  private _appRef = inject(ApplicationRef);
+  private _environmentInjector = inject(EnvironmentInjector);
+
+  /**
+   * Loads a set of styles.
+   * @param loader Component which will be instantiated to load the styles.
+   */
+  load(loader: Type<unknown>): void {
+    let data = appsWithLoaders.get(this._appRef);
+
+    // If we haven't loaded for this app before, we have to initialize it.
+    if (!data) {
+      data = {loaders: new Set(), refs: []};
+      appsWithLoaders.set(this._appRef, data);
+
+      // When the app is destroyed, we need to clean up all the related loaders.
+      this._appRef.onDestroy(() => {
+        appsWithLoaders.get(this._appRef)?.refs.forEach(ref => ref.destroy());
+        appsWithLoaders.delete(this._appRef);
+      });
+    }
+
+    // If the loader hasn't been loaded before, we need to instatiate it.
+    if (!data.loaders.has(loader)) {
+      data.loaders.add(loader);
+      data.refs.push(createComponent(loader, {environmentInjector: this._environmentInjector}));
+    }
+  }
+}

tools/public_api_guard/cdk/private.md

@@ -0,0 +1,21 @@
+## API Report File for "components-srcs"
+
+> Do not edit this file. It is a report generated by [API Extractor](https://api-extractor.com/).
+
+```ts
+
+import * as i0 from '@angular/core';
+import { Type } from '@angular/core';
+
+// @public
+export class _CdkPrivateStyleLoader {
+    load(loader: Type<unknown>): void;
+    // (undocumented)
+    static ɵfac: i0.ɵɵFactoryDeclaration<_CdkPrivateStyleLoader, never>;
+    // (undocumented)
+    static ɵprov: i0.ɵɵInjectableDeclaration<_CdkPrivateStyleLoader>;
+}
+
+// (No @packageDocumentation comment for this package)
+
+```