export before class decorator breaks stryker

[Rubenvdbrink]

Summary
When i use export before any class decorator notation stryker will throw errors.

Does work

@Pipe({ name: 'contactName', standalone: true })
export class ContactNamePipe implements PipeTransform {
    transform(value: Contact) : string {
        return `${value.firstName} ${value.surname}`;
    }
}

this does not work

export @Pipe({ name: 'contactName', standalone: true })
class ContactNamePipe implements PipeTransform {
    transform(value: Contact) : string {
        return `${value.firstName} ${value.surname}`;
    }
}

Stryker config

{
  "$schema": "./node_modules/@stryker-mutator/core/schema/stryker-schema.json",
  "_comment": "This config was generated using 'stryker init'. Please see the guide for more information: https://stryker-mutator.io/docs/stryker-js/guides/angular",
  "mutate": [
    "src/**/*.ts",
    "!src/**/*.spec.ts",
    "!src/test.ts",
    "!src/environments/*.ts"
  ],
  "testRunner": "karma",
  "karma": {
    "configFile": "karma.conf.js",
    "projectType": "angular-cli",
    "config": {
      "browsers": [
        "ChromeHeadless"
      ]
    }
  },
  "reporters": [
    "progress",
    "clear-text",
    "html"
  ],
  "concurrency": 10,
  "concurrency_comment": "Recommended to use about half of your available cores when running stryker with angular",
  "coverageAnalysis": "perTest"
}

Test runner config

// Karma configuration file, see link for more information
// https://karma-runner.github.io/1.0/config/configuration-file.html

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: {
// you can add configuration options for Jasmine here
// the possible options are listed at https://jasmine.github.io/api/edge/Configuration.html
// for example, you can disable the random execution with random: false
// or set a specific seed with seed: 4321
},
clearContext: false // leave Jasmine Spec Runner output visible in browser
},
jasmineHtmlReporter: {
suppressAll: true // removes the duplicated traces
},
coverageReporter: {
dir: require('path').join(__dirname, './coverage/date-picker'),
subdir: '.',
reporters: [
{ type: 'html' },
{ type: 'text-summary' }
]
},
reporters: ['progress', 'kjhtml'],
browsers: ['Chrome'],
restartOnFileChange: true
});
};

Stryker environment

@stryker-mutator/karma-runner@8.2.6

jasmine@5.1.0

Test runner environment

# stryker run

Your Environment

software	version(s)
node	v20.14.0
npm	v10.2.5
Operating System	windows 11 enterprise 10.0.22621

Add stryker.log

11:47:52 (2912) DEBUG ConfigReader Loading config from stryker.config.json
11:47:52 (2912) DEBUG ConfigReader Loaded config: {
  "$schema": "./node_modules/@stryker-mutator/core/schema/stryker-schema.json",
  "_comment": "This config was generated using 'stryker init'. Please see the guide for more information: https://stryker-mutator.io/docs/stryker-js/guides/angular",
  "mutate": [
    "src/**/*.ts",
    "!src/**/*.spec.ts",
    "!src/test.ts",
    "!src/environments/*.ts"
  ],
  "testRunner": "karma",
  "karma": {
    "configFile": "karma.conf.js",
    "projectType": "angular-cli",
    "config": {
      "browsers": [
        "ChromeHeadless"
      ]
    }
  },
  "reporters": [
    "progress",
    "clear-text",
    "html"
  ],
  "concurrency": 10,
  "concurrency_comment": "Recommended to use about half of your available cores when running stryker with angular",
  "coverageAnalysis": "perTest",
  "fileLogLevel": "trace",
  "allowConsoleColors": true,
  "checkers": [],
  "checkerNodeArgs": [],
  "commandRunner": {
    "command": "npm test"
  },
  "clearTextReporter": {
    "allowColor": true,
    "allowEmojis": false,
    "logTests": true,
    "maxTestsToLog": 3,
    "reportTests": true,
    "reportMutants": true,
    "reportScoreTable": true
  },
  "dashboard": {
    "baseUrl": "https://dashboard.stryker-mutator.io/api/reports",
    "reportType": "full"
  },
  "dryRunOnly": false,
  "eventReporter": {
    "baseDir": "reports/mutation/events"
  },
  "ignorePatterns": [],
  "ignoreStatic": false,
  "incremental": false,
  "incrementalFile": "reports/stryker-incremental.json",
  "force": false,
  "inPlace": false,
  "logLevel": "info",
  "maxConcurrentTestRunners": 9007199254740991,
  "maxTestRunnerReuse": 0,
  "mutator": {
    "plugins": null,
    "excludedMutations": []
  },
  "plugins": [
    "@stryker-mutator/*"
  ],
  "appendPlugins": [],
  "htmlReporter": {
    "fileName": "reports/mutation/mutation.html"
  },
  "jsonReporter": {
    "fileName": "reports/mutation/mutation.json"
  },
  "disableTypeChecks": true,
  "symlinkNodeModules": true,
  "tempDirName": ".stryker-tmp",
  "cleanTempDir": true,
  "testRunnerNodeArgs": [],
  "thresholds": {
    "high": 80,
    "low": 60,
    "break": null
  },
  "timeoutFactor": 1.5,
  "timeoutMS": 5000,
  "dryRunTimeoutMinutes": 5,
  "tsconfigFile": "tsconfig.json",
  "warnings": true,
  "disableBail": false,
  "allowEmpty": false,
  "ignorers": []
}
11:47:52 (2912) DEBUG PluginLoader Loading @stryker-mutator/* from C:\Users\..\date-picker\node_modules\@stryker-mutator
11:47:52 (2912) DEBUG PluginLoader Loading plugin "@stryker-mutator/karma-runner" (matched with expression @stryker-mutator/*)
11:47:52 (2912) DEBUG PluginLoader Loading plugin @stryker-mutator/karma-runner
11:47:52 (2912) DEBUG PluginLoader Loading plugin file:///C:/Users/../date-picker/node_modules/@stryker-mutator/core/dist/src/reporters/index.js
11:47:52 (2912) DEBUG MetaSchemaBuilder Contributing 1 schemas from plugins to options validation.
11:47:52 (2912) WARN ProjectReader Glob pattern "!src/test.ts" did not exclude any files.
11:47:52 (2912) INFO ProjectReader Found 9 of 318 file(s) to be mutated.
11:47:52 (2912) DEBUG ProjectReader All input files: [
  ...
]
11:47:52 (2912) DEBUG ProjectReader Files to mutate: [
  ...
]
11:47:52 (2912) DEBUG TemporaryDirectory Using temp directory "C:\Users\...\date-picker\.stryker-tmp"
11:47:52 (2912) DEBUG Instrumenter Instrumenting 9 source files with mutants
11:47:52 (2912) DEBUG Instrumenter Instrumented src\app\app.component.ts (8 mutant(s))
11:47:52 (2912) DEBUG Instrumenter Instrumented src\app\app.config.ts (4 mutant(s))
11:47:52 (2912) DEBUG Instrumenter Instrumented src\app\app.routes.ts (1 mutant(s))
11:47:52 (2912) DEBUG Instrumenter Instrumented src\app\contact-list\contact-list.component.ts (9 mutant(s))
11:47:52 (2912) DEBUG Stryker Not removing the temp dir because an error occurred
11:47:52 (2912) ERROR Stryker Unexpected error occurred while running Stryker SyntaxError: C:\Users\...\date-picker\src\app\contact-name\contact-name.pipe.ts: Unexpected token, expected "{" (4:7)
...
 {
  code: 'BABEL_PARSE_ERROR',
  reasonCode: 'UnexpectedToken',
  loc: Position { line: 4, column: 7, index: 109 },
  pos: 109
}
11:47:52 (2912) INFO Stryker This might be a known problem with a solution documented in our troubleshooting guide.
11:47:52 (2912) INFO Stryker You can find it at https://stryker-mutator.io/docs/stryker-js/troubleshooting/

[nicojs]

Hi @Rubenvdbrink thanks for opening this issue.

We have reached a dilemma here. We're using Babel under the hood. Babel supports TypeScript using the @babel/preset-typescript. It enables TypeScript features like type annotations but not decorators. We enable decorators separately using the babel-plugin-proposal-decorators.

Decorators have evolved quite a lot over the years, as you can see from the "version" config option: "2023-11", "2023-05", "2023-01", "2022-03", "2021-12", "2018-09" or "legacy". TypeScript was traditionally fully compatible with the "legacy" version of Babel decorators. But since typescript 5.0, decorators are also allowed after the export keyword (as you've figured out). See https://www.typescriptlang.org/docs/handbook/release-notes/typescript-5-0.html#differences-with-experimental-legacy-decorators. There is no way that I know of to get this behavior from Babel's decorator plugin. We can set the version to "2023-11" and that seems to solve it, but then constructor parameter decorators are not allowed (like constructor(@Inject(DOCUMENT) document) {}, since they are notably absent from the current decorator implementation, see the class method parameter decorators proposal

See also ts-parser.ts, where we configure the Babel plugins for TypeScript.

For now, the best we can do is add a remark in troubleshooting.md.

I'll try reaching out to the babel team for help.