feat: load referenced config from package.json (#14044)

CHANGELOG.md

@@ -5,6 +5,7 @@
 - `[jest-circus, jest-cli, jest-config]` Add `waitNextEventLoopTurnForUnhandledRejectionEvents` flag to minimise performance impact of correct detection of unhandled promise rejections introduced in [#14315](https://github.com/jestjs/jest/pull/14315) ([#14681](https://github.com/jestjs/jest/pull/14681))
 - `[jest-config]` [**BREAKING**] Add `mts` and `cts` to default `moduleFileExtensions` config ([#14369](https://github.com/facebook/jest/pull/14369))
 - `[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/core]` [**BREAKING**] Group together open handles with the same stack trace ([#13417](https://github.com/jestjs/jest/pull/13417), & [#14543](https://github.com/jestjs/jest/pull/14543))
 - `[@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

@@ -81,6 +81,15 @@ Alternatively Jest's configuration can be defined through the `"jest"` key in th
 }
 ```
 
+Also Jest's configuration json file can be referenced through the `"jest"` key in the `package.json` of your project:
+
+```json title="package.json"
+{
+  "name": "my-project",
+  "jest": "./path/to/config.json"
+}
+```
+
 ## Options
 
 :::info

packages/jest-config/src/__tests__/resolveConfigPath.test.ts

@@ -112,6 +112,72 @@ describe.each(JEST_CONFIG_EXT_ORDER.slice(0))(
         );
       }).toThrow(NO_ROOT_DIR_ERROR_PATTERN);
     });
+
+    test('file path from "jest" key', () => {
+      const anyFileName = `anyJestConfigfile${extension}`;
+      const relativePackageJsonPath = 'a/b/c/package.json';
+      const relativeAnyFilePath = `a/b/c/conf/${anyFileName}`;
+      const absolutePackageJsonPath = path.resolve(
+        DIR,
+        relativePackageJsonPath,
+      );
+      const absoluteAnyFilePath = path.resolve(DIR, relativeAnyFilePath);
+
+      writeFiles(DIR, {
+        'a/b/c/package.json': `{ "jest": "conf/${anyFileName}" }`,
+      });
+      writeFiles(DIR, {[relativeAnyFilePath]: ''});
+
+      const result = resolveConfigPath(
+        path.dirname(absolutePackageJsonPath),
+        DIR,
+      );
+
+      expect(result).toBe(absoluteAnyFilePath);
+    });
+
+    test('not a file path from "jest" key', () => {
+      const anyFileName = `anyJestConfigfile${extension}`;
+      const relativePackageJsonPath = 'a/b/c/package.json';
+      const relativeAnyFilePath = `a/b/c/conf/${anyFileName}`;
+      const absolutePackageJsonPath = path.resolve(
+        DIR,
+        relativePackageJsonPath,
+      );
+
+      writeFiles(DIR, {
+        'a/b/c/package.json': '{ "jest": {"verbose": true} }',
+      });
+      writeFiles(DIR, {[relativeAnyFilePath]: ''});
+
+      const result = resolveConfigPath(
+        path.dirname(absolutePackageJsonPath),
+        DIR,
+      );
+
+      expect(result).toBe(absolutePackageJsonPath);
+    });
+
+    test('not a valid file when "jest" key is a path', () => {
+      const anyFileName = `anyJestConfigfile${extension}`;
+      const relativePackageJsonPath = 'a/b/c/package.json';
+      const relativeAnyFilePath = `a/b/c/conf/${anyFileName}`;
+      const absolutePackageJsonPath = path.resolve(
+        DIR,
+        relativePackageJsonPath,
+      );
+
+      writeFiles(DIR, {
+        'a/b/c/package.json': '{ "jest": "conf/nonExistentConfigfile.json" }',
+      });
+      writeFiles(DIR, {[relativeAnyFilePath]: ''});
+
+      expect(() =>
+        resolveConfigPath(path.dirname(absolutePackageJsonPath), DIR),
+      ).toThrow(
+        /Jest expects the string configuration to point to a file, but .* not\./,
+      );
+    });
   },
 );
 

packages/jest-config/src/resolveConfigPath.ts

@@ -75,8 +75,33 @@ const resolveConfigPathByTraversing = (
   ).filter(isFile);
 
   const packageJson = findPackageJson(pathToResolve);
-  if (packageJson && hasPackageJsonJestKey(packageJson)) {
-    configFiles.push(packageJson);
+
+  if (packageJson) {
+    const jestKey = getPackageJsonJestKey(packageJson);
+
+    if (jestKey) {
+      if (typeof jestKey === 'string') {
+        const absolutePath = path.isAbsolute(jestKey)
+          ? jestKey
+          : path.resolve(pathToResolve, jestKey);
+
+        if (!isFile(absolutePath)) {
+          throw new ValidationError(
+            `${BULLET}Validation Error`,
+            `  Configuration in ${chalk.bold(packageJson)} is not valid. ` +
+              `Jest expects the string configuration to point to a file, but ${absolutePath} is not. ` +
+              `Please check your Jest configuration in ${chalk.bold(
+                packageJson,
+              )}.`,
+            DOCUMENTATION_NOTE,
+          );
+        }
+
+        configFiles.push(absolutePath);
+      } else {
+        configFiles.push(packageJson);
+      }
+    }
   }
 
   if (!skipMultipleConfigError && configFiles.length > 1) {
@@ -111,14 +136,18 @@ const findPackageJson = (pathToResolve: string) => {
   return undefined;
 };
 
-const hasPackageJsonJestKey = (packagePath: string) => {
-  const content = fs.readFileSync(packagePath, 'utf8');
+const getPackageJsonJestKey = (
+  packagePath: string,
+): Record<string, unknown> | string | undefined => {
   try {
-    return 'jest' in JSON.parse(content);
-  } catch {
-    // If package is not a valid JSON
-    return false;
-  }
+    const content = fs.readFileSync(packagePath, 'utf8');
+    const parsedContent = JSON.parse(content);
+
+    if ('jest' in parsedContent) {
+      return parsedContent.jest;
+    }
+  } catch {}
+  return undefined;
 };
 
 const makeResolutionErrorMessage = (initialPath: string, cwd: string) =>