feat: fetch latest NPM package version except of hardcoding those values

src/schematics/ng-add/index.spec.ts

@@ -58,14 +58,22 @@ describe('ng-add', () => {
     expect(tree.files).toBeDefined();
   });
 
-  test('should add single-spa dependency', async () => {
+  test('should add single-spa to dependencies', async () => {
     const tree = await testRunner
       .runSchematicAsync<NgAddOptions>('ng-add', {}, defaultAppTree)
       .toPromise();
     const packageJSON = JSON.parse(getFileContent(tree, '/package.json'));
     expect(packageJSON.dependencies['single-spa-angular']).toBeDefined();
   });
 
+  test('should add @angular-builders/custom-webpack to devDependencies', async () => {
+    const tree = await testRunner
+      .runSchematicAsync<NgAddOptions>('ng-add', {}, defaultAppTree)
+      .toPromise();
+    const packageJSON = JSON.parse(getFileContent(tree, '/package.json'));
+    expect(packageJSON.devDependencies['@angular-builders/custom-webpack']).toBeDefined();
+  });
+
   test('should add main-single-spa.ts', async () => {
     const tree = await testRunner
       .runSchematicAsync<NgAddOptions>('ng-add', {}, defaultAppTree)

src/schematics/ng-add/index.ts

@@ -11,14 +11,15 @@ import {
   applyTemplates,
   SchematicsException,
 } from '@angular-devkit/schematics';
-import { NodePackageInstallTask } from '@angular-devkit/schematics/tasks';
+
+import { addPackageJsonDependency } from '@schematics/angular/utility/dependencies';
 import { getWorkspace, getWorkspacePath } from '@schematics/angular/utility/config';
-import { normalize, join } from 'path';
 import { WorkspaceProject, Builders, BrowserBuilderOptions } from '@schematics/angular/utility/workspace-models';
 
+import { normalize, join } from 'path';
+
 import { Schema as NgAddOptions } from './schema';
-import * as versions from '../library-versions';
-import { addPackageToPackageJson } from '../utils';
+import { getSingleSpaAngularDependency, getAngularBuildersCustomWebpackDependency } from './npm';
 
 interface CustomWebpackBuilderOptions extends BrowserBuilderOptions {
   customWebpackConfig: {
@@ -28,22 +29,25 @@ interface CustomWebpackBuilderOptions extends BrowserBuilderOptions {
 
 export default function (options: NgAddOptions): Rule {
   return chain([
-    addDependencies(options),
+    addDependencies(),
     createMainEntry(options),
     updateConfiguration(options),
     addNPMScripts(options),
   ]);
 }
 
-export function addDependencies(options: NgAddOptions) {
-  return (host: Tree, context: SchematicContext) => {
-    addPackageToPackageJson(host, 'single-spa-angular', versions.singleSpaAngular);
-    if (atLeastAngular8()) {
-      addPackageToPackageJson(host, '@angular-builders/custom-webpack', versions.angularBuilderCustomWebpack);
+export function addDependencies(): Rule {
+  const dependencies = [
+    getSingleSpaAngularDependency(),
+    getAngularBuildersCustomWebpackDependency(),
+  ];
+
+  return async (tree: Tree, context: SchematicContext) => {
+    for await (const dependency of dependencies) {
+      addPackageJsonDependency(tree, dependency);
+      context.logger.info(`Added '${dependency.name}' as a dependency`);
     }
-    context.addTask(new NodePackageInstallTask());
-    context.logger.info(`Added 'single-spa-angular' as a dependency`);
-  }
+  };
 }
 
 export function createMainEntry(options: NgAddOptions): Rule {

src/schematics/ng-add/npm.ts

@@ -0,0 +1,78 @@
+import * as http from 'http';
+import { NodeDependencyType, NodeDependency } from '@schematics/angular/utility/dependencies';
+
+const LATEST_COMPATIBLE_CUSTOM_WEBPACK_VERSIONS = {
+  // `8.4.1` is the latest version of `@angular-builders/custom-webpack`
+  // that is compatible with Angular 8 and will not change anymore because
+  // 9 version is in active development. We will need to consider choosing
+  // `@angular-builders/custom-webpack` based on the currently used Angular
+  // version.
+  8: '8.4.1',
+};
+
+/**
+ * Actually, there is the `latest-version` package that does the
+ * same stuff, but we'd want these schematics to be lightweight and
+ * less dependent on other packages.
+ */
+function getLatestNodeVersion(name: string) {
+  return new Promise<string>(resolve => {
+    const defaultVersion = 'latest';
+
+    const req = http.get(`http://registry.npmjs.org/${name}`, res => {
+      const chunks: Uint8Array[] = [];
+
+      res.on('data', chunk => {
+        chunks.push(chunk);
+      });
+
+      res.on('end', () => {
+        try {
+          const body = Buffer.concat(chunks).toString();
+          const json = JSON.parse(body);
+          const tags = json['dist-tags'];
+          resolve(tags.latest);
+        } catch {
+          resolve(defaultVersion);
+        }
+      });
+    });
+
+    req.on('error', () => resolve(defaultVersion));
+    req.end();
+  });
+}
+
+/**
+ * We're interested in installing the latest `single-spa-angular` version.
+ */
+export async function getSingleSpaAngularDependency(): Promise<NodeDependency> {
+  const name = 'single-spa-angular';
+  const version = await getLatestNodeVersion(name);
+
+  return {
+    name,
+    version,
+    overwrite: false,
+    type: NodeDependencyType.Default,
+  };
+}
+
+/**
+ * We have to install `@angular-builders/custom-webpack` version compatible with the current
+ * version of Angular. If Angular is 8 then `custom-webpack@8.4.1` has to be installed.
+ */
+export async function getAngularBuildersCustomWebpackDependency(): Promise<NodeDependency> {
+  const { VERSION } = require('@angular/core');
+  const name = '@angular-builders/custom-webpack';
+
+  const version =
+    LATEST_COMPATIBLE_CUSTOM_WEBPACK_VERSIONS[VERSION.major] || (await getLatestNodeVersion(name));
+
+  return {
+    name,
+    version,
+    overwrite: false,
+    type: NodeDependencyType.Dev,
+  };
+}