fix(@schematics/angular): defer karma config deletion in Karma to Vitest migration

This commit resolves a race condition in the Karma-to-Vitest migration where shared configuration files were deleted prematurely within the schematic transaction. Previously, the routine erased the target file upon discovering it was identical to boilerplate, which blinded other referring projects to extraction metadata.

The solution introduces analysis object caching so AST parsing occurs exactly once per discrete path. Deletion operations are deferred and batch-executed at the end of workspace processing. This mechanism guarantees continuous readability across iterating dependencies and yields operational speed improvements via memoized checks.

Author: clydin

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

@@ -119,42 +119,47 @@ function extractCoverageSettings(
   }
 }
 
+export interface KarmaConfigProcessingResult {
+  analysis: KarmaConfigAnalysis;
+  isRemovable: boolean;
+}
+
 export async function processKarmaConfig(
   karmaConfig: string,
   options: Record<string, json.JsonValue | undefined>,
   projectName: string,
   context: SchematicContext,
   tree: Tree,
-  removableKarmaConfigs: Map<string, boolean>,
+  cache: Map<string, KarmaConfigProcessingResult>,
   needDevkitPlugin: boolean,
   manualMigrationFiles: string[],
 ): Promise<void> {
-  if (tree.exists(karmaConfig)) {
+  let cachedResult = cache.get(karmaConfig);
+
+  if (!cachedResult && tree.exists(karmaConfig)) {
     const content = tree.readText(karmaConfig);
     const analysis = analyzeKarmaConfig(content);
 
-    extractReporters(analysis, options, projectName, context);
-    extractCoverageSettings(analysis, options, projectName, context);
-
-    let isRemovable = removableKarmaConfigs.get(karmaConfig);
-    if (isRemovable === undefined) {
-      if (analysis.hasUnsupportedValues) {
-        isRemovable = false;
-      } else {
-        const diff = await compareKarmaConfigToDefault(
-          analysis,
-          projectName,
-          karmaConfig,
-          needDevkitPlugin,
-        );
-        isRemovable = !hasDifferences(diff) && diff.isReliable;
-      }
-      removableKarmaConfigs.set(karmaConfig, isRemovable);
+    let isRemovable = false;
+    if (!analysis.hasUnsupportedValues) {
+      const diff = await compareKarmaConfigToDefault(
+        analysis,
+        projectName,
+        karmaConfig,
+        needDevkitPlugin,
+      );
+      isRemovable = !hasDifferences(diff) && diff.isReliable;
     }
 
-    if (isRemovable) {
-      tree.delete(karmaConfig);
-    } else {
+    cachedResult = { analysis, isRemovable };
+    cache.set(karmaConfig, cachedResult);
+  }
+
+  if (cachedResult) {
+    extractReporters(cachedResult.analysis, options, projectName, context);
+    extractCoverageSettings(cachedResult.analysis, options, projectName, context);
+
+    if (!cachedResult.isRemovable) {
       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 ` +
@@ -164,5 +169,6 @@ export async function processKarmaConfig(
       manualMigrationFiles.push(karmaConfig);
     }
   }
+
   delete options['karmaConfig'];
 }

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

@@ -14,14 +14,14 @@ import { latestVersions } from '../../utility/latest-versions';
 import { TargetDefinition, allTargetOptions, updateWorkspace } from '../../utility/workspace';
 import { Builders } from '../../utility/workspace-models';
 import { BUILD_OPTIONS_KEYS } from './constants';
-import { processKarmaConfig } from './karma-processor';
+import { KarmaConfigProcessingResult, processKarmaConfig } from './karma-processor';
 
 async function processTestTargetOptions(
   testTarget: TargetDefinition,
   projectName: string,
   context: SchematicContext,
   tree: Tree,
-  removableKarmaConfigs: Map<string, boolean>,
+  removableKarmaConfigs: Map<string, KarmaConfigProcessingResult>,
   customBuildOptions: Record<string, Record<string, json.JsonValue | undefined>>,
   needDevkitPlugin: boolean,
   manualMigrationFiles: string[],
@@ -122,7 +122,7 @@ async function processTestTargetOptions(
 function updateProjects(tree: Tree, context: SchematicContext): Rule {
   return updateWorkspace(async (workspace) => {
     let needsCoverage = false;
-    const removableKarmaConfigs = new Map<string, boolean>();
+    const removableKarmaConfigs = new Map<string, KarmaConfigProcessingResult>();
     const migratedProjects: string[] = [];
     const skippedNonApplications: string[] = [];
     const skippedMissingAppBuilder: string[] = [];
@@ -235,6 +235,13 @@ function updateProjects(tree: Tree, context: SchematicContext): Rule {
       migratedProjects.push(projectName);
     }
 
+    // Perform cleanup of removable karma config files
+    for (const [configPath, result] of removableKarmaConfigs) {
+      if (result.isRemovable && tree.exists(configPath)) {
+        tree.delete(configPath);
+      }
+    }
+
     // Log summary
     context.logger.info('\n--- Karma to Vitest Migration Summary ---');
     context.logger.info(`Projects migrated: ${migratedProjects.length}`);

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

@@ -322,6 +322,7 @@ module.exports = function (config) {
     const newTree = await schematicRunner.runSchematic('migrate-karma-to-vitest', {}, tree);
     expect(newTree.exists('karma.conf.js')).toBeFalse();
   });
+
   it('should shift main compilation entry file directly into setupFiles array', async () => {
     const { projects } = tree.readJson('/angular.json') as any;
     projects.app.targets.test.options.main = 'src/test.ts';
@@ -333,6 +334,7 @@ module.exports = function (config) {
     expect(newProjects.app.targets.test.options.setupFiles).toEqual(['src/test.ts']);
     expect(newProjects.app.targets.test.options.main).toBeUndefined();
   });
+
   it('should generate unique testing configuration name preventing collision overwrites', async () => {
     const { projects } = tree.readJson('/angular.json') as any;
     projects.app.targets.build.configurations = {
@@ -350,6 +352,7 @@ module.exports = function (config) {
     ]);
     expect(newProjects.app.targets.test.options.buildTarget).toBe(':build:testing-2');
   });
+
   it('should inject @vitest/coverage-v8 whenever coverage presence is detected', async () => {
     const { projects } = tree.readJson('/angular.json') as any;
     projects.app.targets.test.options.codeCoverage = true;
@@ -360,4 +363,61 @@ module.exports = function (config) {
 
     expect(devDependencies['@vitest/coverage-v8']).toBe(latestVersions['@vitest/coverage-v8']);
   });
+
+  it('should successfully extract settings across multiple projects sharing the same removable karma config', async () => {
+    const { projects } = tree.readJson('/angular.json') as any;
+    projects.app.targets.test.builder = '@angular-devkit/build-angular:karma';
+
+    // Add a second project sharing the exact same configuration
+    projects.app2 = {
+      ...JSON.parse(JSON.stringify(projects.app)),
+      root: 'app2',
+    };
+
+    tree.overwrite('/angular.json', JSON.stringify({ version: 1, projects }));
+
+    const DEFAULT_KARMA_CONFIG = `
+module.exports = function (config) {
+  config.set({
+    basePath: '',
+    frameworks: ['jasmine', '@angular-devkit/build-angular'],
+    plugins: [
+      require('karma-jasmine'),
+      require('karma-chrome-launcher'),
+      require('karma-jasmine-html-reporter'),
+      require('karma-coverage'),
+      require('@angular-devkit/build-angular/plugins/karma')
+    ],
+    client: {
+      jasmine: {},
+    },
+    jasmineHtmlReporter: {
+      suppressAll: true
+    },
+    coverageReporter: {
+      dir: require('path').join(__dirname, './coverage/app'),
+      subdir: '.',
+      reporters: [
+        { type: 'html' },
+        { type: 'text-summary' }
+      ]
+    },
+    reporters: ['progress', 'kjhtml'],
+    browsers: ['Chrome'],
+    restartOnFileChange: true
+  });
+};
+`;
+    tree.create('karma.conf.js', DEFAULT_KARMA_CONFIG);
+
+    const newTree = await schematicRunner.runSchematic('migrate-karma-to-vitest', {}, tree);
+    const { projects: newProjects } = newTree.readJson('/angular.json') as any;
+
+    // Assert BOTH projects got the extraction logic mapped correctly
+    expect(newProjects.app.targets.test.options.reporters).toEqual(['default']);
+    expect(newProjects.app2.targets.test.options.reporters).toEqual(['default']);
+
+    // Assert that the deletion deferred successfully until BOTH extracted the data
+    expect(newTree.exists('karma.conf.js')).toBeFalse();
+  });
 });