feat: allow passing TS config loader options (#15234)

Author: k-rajat19

CHANGELOG.md

@@ -12,9 +12,9 @@
 - `[jest-config]` [**BREAKING**] Update `testMatch` and `testRegex` default option for supporting `mjs`, `cjs`, `mts`, and `cts` ([#14584](https://github.com/jestjs/jest/pull/14584))
 - `[jest-config]` Loads config file from provided path in `package.json` ([#14044](https://github.com/facebook/jest/pull/14044))
 - `[jest-config]` Allow loading `jest.config.cts` files ([#14070](https://github.com/facebook/jest/pull/14070))
-- `[jest-config]` Added an option to disable `ts-node` typechecking ([#15161](https://github.com/jestjs/jest/pull/15161))
 - `[jest-config]` Show `rootDir` in error message when a `preset` fails to load ([#15194](https://github.com/jestjs/jest/pull/15194))
 - `[jest-config]` Support loading TS config files using `esbuild-register` via docblock loader ([#15190](https://github.com/jestjs/jest/pull/15190))
+- `[jest-config]` allow passing TS config loader options via docblock comment ([#15234](https://github.com/jestjs/jest/pull/15234))
 - `[@jest/core]` Group together open handles with the same stack trace ([#13417](https://github.com/jestjs/jest/pull/13417), & [#14789](https://github.com/jestjs/jest/pull/14789))
 - `[@jest/core]` Add `perfStats` to surface test setup overhead ([#14622](https://github.com/jestjs/jest/pull/14622))
 - `[@jest/core]` [**BREAKING**] Changed `--filter` to accept an object with shape `{ filtered: Array<string> }` to match [documentation](https://jestjs.io/docs/cli#--filterfile) ([#13319](https://github.com/jestjs/jest/pull/13319))

docs/Configuration.md

@@ -73,7 +73,20 @@ const config: Config = {
 export default config;
 ```
 
-If you are using `ts-node`, you can set `JEST_CONFIG_TRANSPILE_ONLY` environment variable to `true` (case insensitive) to read configuration files without typechecking.
+You can also pass options to the loader, for instance to enable `transpileOnly`.
+
+```ts title="jest.config.ts"
+/** @jest-config-loader ts-node */
+/** @jest-config-loader-options {"transpileOnly": true} */
+
+import type {Config} from 'jest';
+
+const config: Config = {
+  verbose: true,
+};
+
+export default config;
+```
 
 :::
 

e2e/__tests__/jest.config.ts.test.ts

@@ -84,6 +84,7 @@ const jestTypesExists = fs.existsSync(jestTypesPath);
     writeFiles(DIR, {
       '__tests__/a-giraffe.js': "test('giraffe', () => expect(1).toBe(1));",
       'jest.config.ts': `
+      /**@jest-config-loader-options {"transpileOnly":${!!skipTypeCheck}}*/
       import {Config} from 'jest';
       const config: Config = { testTimeout: "10000" };
       export default config;
@@ -95,11 +96,7 @@ const jestTypesExists = fs.existsSync(jestTypesPath);
       "TS2322: Type 'string' is not assignable to type 'number'.";
     const runtimeErrorString = 'Option "testTimeout" must be of type:';
 
-    const {stderr, exitCode} = runJest(DIR, ['-w=1', '--ci=false'], {
-      env: {
-        JEST_CONFIG_TRANSPILE_ONLY: skipTypeCheck ? 'true' : undefined,
-      },
-    });
+    const {stderr, exitCode} = runJest(DIR, ['-w=1', '--ci=false']);
 
     if (skipTypeCheck) {
       expect(stderr).not.toMatch(typeErrorString);

packages/jest-config/src/readConfigFileAndSetRootDir.ts

@@ -89,13 +89,19 @@ export default async function readConfigFileAndSetRootDir(
 }
 
 // Load the TypeScript configuration
+let extraTSLoaderOptions: Record<string, unknown>;
+
 const loadTSConfigFile = async (
   configPath: string,
 ): Promise<Config.InitialOptions> => {
   // Get registered TypeScript compiler instance
   const docblockPragmas = parse(extract(fs.readFileSync(configPath, 'utf8')));
   const tsLoader = docblockPragmas['jest-config-loader'] || 'ts-node';
+  const docblockTSLoaderOptions = docblockPragmas['jest-config-loader-options'];
 
+  if (typeof docblockTSLoaderOptions === 'string') {
+    extraTSLoaderOptions = JSON.parse(docblockTSLoaderOptions);
+  }
   if (Array.isArray(tsLoader)) {
     throw new TypeError(
       `Jest: You can only define a single loader through docblocks, got "${tsLoader.join(
@@ -143,8 +149,7 @@ async function registerTsLoader(loader: TsLoaderModule): Promise<TsLoader> {
         moduleTypes: {
           '**': 'cjs',
         },
-        transpileOnly:
-          process.env.JEST_CONFIG_TRANSPILE_ONLY?.toLowerCase() === 'true',
+        ...extraTSLoaderOptions,
       });
     } else if (loader === 'esbuild-register') {
       const tsLoader = await import(
@@ -158,6 +163,7 @@ async function registerTsLoader(loader: TsLoaderModule): Promise<TsLoader> {
           if (bool) {
             instance = tsLoader.register({
               target: `node${process.version.slice(1)}`,
+              ...extraTSLoaderOptions,
             });
           } else {
             instance?.unregister();