angular/angular-cli · warning

Project " " uses a custom coverage reporter " ". This…

Error message

Project "${projectName}" uses a custom coverage reporter "${type}". This reporter cannot be automatically mapped to Vitest. Please check the Vitest documentation for equivalent coverage reporters.

What it means

During the Karma-to-Vitest migration, extractCoverageSettings maps Karma coverage reporters to Vitest-supported ones. When a karma.conf.js declares a coverage reporter type not in SUPPORTED_COVERAGE_REPORTERS, this warning tells you the reporter cannot be auto-mapped and you must pick an equivalent Vitest/istanbul reporter yourself.

Solutions

1. Open the project's karma.conf.js and note the custom coverageReporter.type
2. Set an equivalent supported reporter in the generated Vitest coverage config (e.g. via vitest-base.config.ts or the test builder's coverageReporters option: ['html','lcov','text'])
3. Replace CI-specific reporters with nyc/istanbul equivalents supported by Vitest (e.g. cobertura -> 'clover'/'lcov' plus a conversion step, teamcity -> 'text' parsed by CI)
4. Re-run or complete the migration and verify coverage output matches your CI expectations

Example fix

// before (karma.conf.js)
coverageReporter: { type: 'teamcity' }
// after (vitest config / builder options)
test: { coverage: { reporter: ['text', 'lcov'] } }

// before migrating, check your karma reporters
const types = (karmaConfig.coverageReporter?.type || []);
const supported = new Set(['clover','cobertura','lcov','lcovonly','html','json','json-summary','text','text-summary','teamcity','none']);
const unsupported = [].concat(types).filter(t => !supported.has(t));
if (unsupported.length) console.warn('Manual coverage reporter mapping needed:', unsupported);

When it happens

Trigger: Running the migrate-karma-to-vitest migration (via processKarmaConfig -> extractCoverageSettings) on a project whose karma.conf.js coverageReporter.type is a custom value not in the supported set (e.g. 'json-summary' variants, 'lcovonly', 'teamcity', or custom reporter names).

Common situations: Projects with customized karma-coverage setups (html+lcovonly combos, CI-specific reporters like teamcity or cobertura, third-party reporters) migrating from Karma/ Jasmine to Vitest on Angular CLI upgrades.

Related errors

• - ${file}
• Project " " uses a custom Karma configuration file " "…
• The following Karma configuration files require manual…
• Cannot add a Vitest configuration as builder for "test"…
• - x

AI-assisted analysis of angular/angular-cli@bb72145f9a (2026-08-30). Data as JSON: /api/errors/b18126f04296b786. Report an issue: GitHub.

Appendix: source

Thrown at packages/schematics/angular/migrations/migrate-karma-to-vitest/karma-processor.ts:86

  // Extract coverage reporters
  const covReporters = (coverageReporter as Record<string, unknown>)['reporters'];
  if (Array.isArray(covReporters)) {
    const mappedCovReporters: string[] = [];
    for (const r of covReporters) {
      let type: string | undefined;
      if (typeof r === 'object' && r !== null && 'type' in r) {
        if (typeof r['type'] === 'string') {
          type = r['type'];
        }
      } else if (typeof r === 'string') {
        type = r;
      }

      if (type) {
        if (SUPPORTED_COVERAGE_REPORTERS.has(type)) {
          mappedCovReporters.push(type);
        } else {
          context.logger.warn(
            `Project "${projectName}" uses a custom coverage reporter "${type}". ` +
              `This reporter cannot be automatically mapped to Vitest. ` +
              `Please check the Vitest documentation for equivalent coverage reporters.`,
          );
        }
      }
    }
    if (mappedCovReporters.length > 0) {
      options['coverageReporters'] = [...new Set(mappedCovReporters)];
    }
  }

  // Extract coverage thresholds
  const check = (coverageReporter as Record<string, unknown>)['check'];
  if (typeof check === 'object' && check !== null) {
    const global = (check as Record<string, unknown>)['global'];
    if (typeof global === 'object' && global !== null) {
      const thresholds: Record<string, number> = {};

View on GitHub (pinned to bb72145f9a)