angular/angular-cli · warning

Unable to update custom karma configuration file ("${karmaCo

Error message

Unable to update custom karma configuration file ("${karmaConfigFile}"). Reason: ${error.message}
References to the "@angular-devkit/build-angular" package within the file may need to be removed manually.

What it means

During the use-application-builder migration, custom karma.conf files are rewritten to drop references to @angular-devkit/build-angular. If rewriting (require() of the config or tree.overwrite) fails, this warning reports the reason and tells you the references may need manual removal.

Source

Thrown at packages/schematics/angular/migrations/use-application-builder/migration.ts:326

          continue;
        }

        try {
          const originalKarmaConfigText = tree.readText(karmaConfigFile);
          const updatedKarmaConfigText = originalKarmaConfigText
            .replaceAll(`require('@angular-devkit/build-angular/plugins/karma'),`, '')
            .replaceAll(`require('@angular-devkit/build-angular/plugins/karma')`, '');

          if (updatedKarmaConfigText.includes('@angular-devkit/build-angular/plugins')) {
            throw new Error(
              'Migration does not support found usage of "@angular-devkit/build-angular".',
            );
          } else {
            tree.overwrite(karmaConfigFile, updatedKarmaConfigText);
          }
        } catch (error) {
          const reason = error instanceof Error ? `Reason: ${error.message}` : '';
          context.logger.warn(
            `Unable to update custom karma configuration file ("${karmaConfigFile}"). ` +
              reason +
              '\nReferences to the "@angular-devkit/build-angular" package within the file may need to be removed manually.',
          );
        }
      }
    }

    return chain(rules);
  });
}

function deleteFile(path: string): Rule {
  return (tree) => {
    tree.delete(path);
  };
}

View on GitHub (pinned to bb72145f9a)

Solutions

1. Open the named karma config file and manually remove/replace references to @angular-devkit/build-angular (e.g. switch to @angular/build unit-test builder).
2. Simplify the karma.conf (remove conditional/dynamic code) and re-run the migration.
3. Convert exotic syntax (ESM/TS) in the config to plain CommonJS JS.
4. Ensure the file is writable and not read-only.

Example fix

// before (karma.conf.js)
const { customKarma } = require('@angular-devkit/build-angular');
// after
module.exports = function (config) { config.set({ basePath: '', frameworks: ['jasmine'] }); };

const src = fs.readFileSync(karmaConfigFile, 'utf8'); if (src.includes('@angular-devkit/build-angular')) console.warn(`${karmaConfigFile} references build-angular; expect migration rewrite`);

function isErrorWithMessage(e: unknown): e is Error { return e instanceof Error; }

try { tree.overwrite(karmaConfigFile, updatedKarmaConfigText); } catch (error) { const reason = error instanceof Error ? `Reason: ${error.message}` : ''; logger.warn(`Unable to update custom karma configuration file ("${karmaConfigFile}"). ${reason}`); }

When it happens

Trigger: The karma config transformation throws — e.g. the karma.conf.js uses syntax the transformer cannot handle, executes code at load time that throws, or the file cannot be parsed/written.

Common situations: Highly customized karma.conf.js with conditional logic, imports of local modules, or ES module syntax where CJS is expected; karma.conf TypeScript variants; files with unusual encodings.

Related errors

• Cannot update project "${projectName}" to use the applicatio
• Project "${options.project}" is configured to use Karma. Ple
• Failed to automatically update types in "${tsConfigPath}". P
• Project "${projectName}" uses the "kjhtml" reporter. This ha
• Project "${projectName}" uses a custom Karma reporter "${r}"

AI-assisted analysis of angular/angular-cli@bb72145f9a (2026-08-30). Data as JSON: /api/errors/035855963955db45. Report an issue: GitHub.