feat(@schematics/angular): add migrate-karma-to-vitest update migration

Migrate projects using the Karma unit-test builder to the new
@angular/build:unit-test builder with Vitest.

This migration automatically updates target builders, translates builder options
(such as coverage and browsers format), moves custom build options to dedicated
configurations to prevent loss of custom settings, cleans up default
configuration files, and installs required Vitest runner packages.

Author: clydin

packages/schematics/angular/migrations/migrate-karma-to-vitest/migration.ts

@@ -0,0 +1,213 @@
+/**
+ * @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.dev/license
+ */
+
+import type { json } from '@angular-devkit/core';
+import { Rule, SchematicContext, Tree, chain } from '@angular-devkit/schematics';
+import { DependencyType, ExistingBehavior, addDependency } from '../../utility/dependency';
+import { latestVersions } from '../../utility/latest-versions';
+import { allTargetOptions, updateWorkspace } from '../../utility/workspace';
+import { Builders } from '../../utility/workspace-models';
+import { analyzeKarmaConfig } from '../karma/karma-config-analyzer';
+import { compareKarmaConfigToDefault, hasDifferences } from '../karma/karma-config-comparer';
+
+function updateProjects(tree: Tree, context: SchematicContext): Rule {
+  return updateWorkspace(async (workspace) => {
+    let hasMigratedAny = false;
+    let needsCoverage = false;
+    const removableKarmaConfigs = new Map<string, boolean>();
+
+    for (const [projectName, project] of workspace.projects) {
+      // Find the test target to migrate
+      const testTarget = project.targets.get('test');
+      if (!testTarget) {
+        continue;
+      }
+
+      let isKarma = false;
+      let needDevkitPlugin = false;
+      // Check if target uses legacy Karma builders
+      switch (testTarget.builder) {
+        case Builders.Karma:
+          isKarma = true;
+          needDevkitPlugin = true;
+          break;
+        case Builders.BuildKarma:
+          isKarma = true;
+          break;
+      }
+
+      if (!isKarma) {
+        continue;
+      }
+
+      // Store custom build options to move to a new build configuration if needed
+      // Match Karma behavior where AOT was disabled by default
+      const customBuildOptions: Record<string, json.JsonValue | undefined> = {
+        aot: false,
+        optimization: false,
+        extractLicenses: false,
+      };
+      // List of build options that are supported by the new unit-test builder
+      const buildOptionsKeys = [
+        'assets',
+        'styles',
+        'scripts',
+        'polyfills',
+        'inlineStyleLanguage',
+        'stylePreprocessorOptions',
+        'externalDependencies',
+        'loader',
+        'define',
+        'fileReplacements',
+        'webWorkerTsConfig',
+        'aot',
+      ];
+
+      for (const [, options] of allTargetOptions(testTarget, false)) {
+        // Collect custom build options
+        for (const key of buildOptionsKeys) {
+          if (options[key] !== undefined) {
+            customBuildOptions[key] = options[key];
+            delete options[key];
+          }
+        }
+
+        // Map Karma options to Unit-Test options
+        if (options['codeCoverage'] !== undefined) {
+          options['coverage'] = options['codeCoverage'];
+          delete options['codeCoverage'];
+        }
+
+        if (options['codeCoverageExclude'] !== undefined) {
+          options['coverageExclude'] = options['codeCoverageExclude'];
+          delete options['codeCoverageExclude'];
+        }
+
+        if (options['coverage'] === true || options['coverageExclude'] !== undefined) {
+          needsCoverage = true;
+        }
+
+        if (options['sourceMap'] !== undefined) {
+          context.logger.info(
+            `Project "${projectName}" has "sourceMap" set for tests. ` +
+              `In unit-test builder with Vitest, source maps are always enabled. The option has been removed.`,
+          );
+          delete options['sourceMap'];
+        }
+
+        // Convert browser list to array format if it is a comma-separated string
+        const browsers = options['browsers'];
+        if (typeof browsers === 'string') {
+          options['browsers'] = browsers.split(',').map((b) => b.trim());
+        } else if (browsers === false) {
+          options['browsers'] = [];
+        }
+
+        // Check if the karma configuration file can be safely removed
+        const karmaConfig = options['karmaConfig'];
+        if (typeof karmaConfig === 'string') {
+          let isRemovable = removableKarmaConfigs.get(karmaConfig);
+          if (isRemovable === undefined && tree.exists(karmaConfig)) {
+            const content = tree.readText(karmaConfig);
+            const analysis = analyzeKarmaConfig(content);
+
+            if (analysis.hasUnsupportedValues) {
+              isRemovable = false;
+            } else {
+              const diff = await compareKarmaConfigToDefault(
+                analysis,
+                projectName,
+                karmaConfig,
+                needDevkitPlugin,
+              );
+              isRemovable = !hasDifferences(diff) && diff.isReliable;
+            }
+            removableKarmaConfigs.set(karmaConfig, isRemovable);
+          }
+
+          if (isRemovable) {
+            tree.delete(karmaConfig);
+          } else {
+            context.logger.warn(
+              `Project "${projectName}" uses a custom Karma configuration file "${karmaConfig}". ` +
+                `Tests have been migrated to use Vitest, but you may need to manually migrate custom settings ` +
+                `from this Karma config to a Vitest config (e.g. vitest.config.ts).`,
+            );
+          }
+        }
+
+        // Map the main entry file to the setupFiles of the unit-test builder
+        const mainFile = options['main'];
+        if (typeof mainFile === 'string') {
+          options['setupFiles'] = [...((options['setupFiles'] as string[]) || []), mainFile];
+
+          context.logger.info(
+            `Project "${projectName}" uses a "main" entry file for tests: "${mainFile}". ` +
+              `This has been mapped to the unit-test builder "setupFiles" array. ` +
+              `Please ensure you remove any TestBed.initTestEnvironment calls from this file ` +
+              `as the builder now handles test environment initialization automatically.`,
+          );
+        }
+        delete options['main'];
+      }
+
+      // If we have custom build options, create a testing configuration
+      if (Object.keys(customBuildOptions).length > 0) {
+        const buildTarget = project.targets.get('build');
+        if (buildTarget) {
+          buildTarget.configurations ??= {};
+
+          let configName = 'testing';
+          if (buildTarget.configurations[configName]) {
+            let counter = 1;
+            while (buildTarget.configurations[`${configName}-${counter}`]) {
+              counter++;
+            }
+            configName = `${configName}-${counter}`;
+          }
+
+          buildTarget.configurations[configName] = { ...customBuildOptions };
+
+          testTarget.options ??= {};
+          testTarget.options['buildTarget'] = `:build:${configName}`;
+        }
+      }
+
+      // Update builder
+      testTarget.builder = '@angular/build:unit-test';
+      testTarget.options ??= {};
+      testTarget.options['runner'] = 'vitest';
+
+      hasMigratedAny = true;
+    }
+
+    if (hasMigratedAny) {
+      const rules = [
+        addDependency('vitest', latestVersions['vitest'], {
+          type: DependencyType.Dev,
+          existing: ExistingBehavior.Skip,
+        }),
+      ];
+
+      if (needsCoverage) {
+        rules.push(
+          addDependency('@vitest/coverage-v8', latestVersions['@vitest/coverage-v8'], {
+            type: DependencyType.Dev,
+            existing: ExistingBehavior.Skip,
+          }),
+        );
+      }
+
+      return chain(rules);
+    }
+  });
+}
+
+export default function (): Rule {
+  return updateProjects;
+}