fix: ensure defaults are set in @babel/eslint-parser (#11970)

* fix: ensure defaults are set in @babel/eslint-parser

* Address feedback

* Update eslint config normalization

eslint/babel-eslint-parser/src/configuration.js

@@ -1,15 +1,24 @@
 import { loadPartialConfig } from "@babel/core";
 
 export function normalizeESLintConfig(options) {
-  const defaultOptions = {
-    babelOptions: {},
-    ecmaVersion: 2020,
-    sourceType: "module",
-    allowImportExportEverywhere: false,
-    requireConfigFile: true,
-  };
+  const {
+    babelOptions = {},
+    // ESLint sets ecmaVersion: undefined when ecmaVersion is not set in the config.
+    ecmaVersion = 2020,
+    sourceType = "module",
+    allowImportExportEverywhere = false,
+    requireConfigFile = true,
+    ...otherOptions
+  } = options;
 
-  return Object.assign(defaultOptions, options);
+  return {
+    babelOptions,
+    ecmaVersion,
+    sourceType,
+    allowImportExportEverywhere,
+    requireConfigFile,
+    ...otherOptions,
+  };
 }
 
 export function normalizeBabelParseConfig(options) {

eslint/babel-eslint-tests/package.json

@@ -4,7 +4,8 @@
   "description": "Tests for babel/eslint-* packages",
   "license": "MIT",
   "private": true,
-  "devDependencies": {
+  "dependencies": {
+    "@babel/eslint-parser": "^7.11.0",
     "dedent": "^0.7.0",
     "eslint": "^7.5.0",
     "eslint-plugin-import": "^2.22.0"

eslint/babel-eslint-tests/test/integration/eslint/config.js

@@ -0,0 +1,21 @@
+import eslint from "eslint";
+import * as parser from "@babel/eslint-parser";
+
+describe("ESLint config", () => {
+  it('should set ecmaVersion to latest and sourceType to "module" by default', () => {
+    const linter = new eslint.Linter();
+    linter.defineParser("@babel/eslint-parser", parser);
+    // ImportDeclarations result in a parser error if ecmaVersion < 2015 and sourceType != "module".
+    const messages = linter.verify('import { hello } from "greetings"', {
+      parser: "@babel/eslint-parser",
+      parserOptions: {
+        babelOptions: {
+          configFile: require.resolve(
+            "../../../../babel-eslint-shared-fixtures/config/babel.config.js",
+          ),
+        },
+      },
+    });
+    expect(messages.length).toEqual(0);
+  });
+});