Fix XO to not override rules from user's config (#761)

lib/options-manager.js

@@ -348,58 +348,58 @@ const buildXOConfig = options => config => {
 	for (const [rule, ruleConfig] of Object.entries(ENGINE_RULES)) {
 		for (const minVersion of Object.keys(ruleConfig).sort(semver.rcompare)) {
 			if (!options.nodeVersion || semver.intersects(options.nodeVersion, `<${minVersion}`)) {
-				config.baseConfig.rules[rule] = ruleConfig[minVersion];
+				config.baseConfig.rules[rule] ??= ruleConfig[minVersion];
 			}
 		}
 	}
 
 	if (options.nodeVersion) {
-		config.baseConfig.rules['n/no-unsupported-features/es-builtins'] = ['error', {version: options.nodeVersion}];
-		config.baseConfig.rules['n/no-unsupported-features/es-syntax'] = ['error', {version: options.nodeVersion, ignores: ['modules']}];
-		config.baseConfig.rules['n/no-unsupported-features/node-builtins'] = ['error', {version: options.nodeVersion}];
+		config.baseConfig.rules['n/no-unsupported-features/es-builtins'] ??= ['error', {version: options.nodeVersion}];
+		config.baseConfig.rules['n/no-unsupported-features/es-syntax'] ??= ['error', {version: options.nodeVersion, ignores: ['modules']}];
+		config.baseConfig.rules['n/no-unsupported-features/node-builtins'] ??= ['error', {version: options.nodeVersion}];
 	}
 
 	if (options.space && !options.prettier) {
 		if (options.ts) {
-			config.baseConfig.rules['@typescript-eslint/indent'] = ['error', spaces, {SwitchCase: 1}];
+			config.baseConfig.rules['@typescript-eslint/indent'] ??= ['error', spaces, {SwitchCase: 1}];
 		} else {
-			config.baseConfig.rules.indent = ['error', spaces, {SwitchCase: 1}];
+			config.baseConfig.rules.indent ??= ['error', spaces, {SwitchCase: 1}];
 		}
 
 		// Only apply if the user has the React plugin
 		if (options.cwd && resolveFrom.silent('eslint-plugin-react', options.cwd)) {
 			config.baseConfig.plugins.push('react');
-			config.baseConfig.rules['react/jsx-indent-props'] = ['error', spaces];
-			config.baseConfig.rules['react/jsx-indent'] = ['error', spaces];
+			config.baseConfig.rules['react/jsx-indent-props'] ??= ['error', spaces];
+			config.baseConfig.rules['react/jsx-indent'] ??= ['error', spaces];
 		}
 	}
 
 	if (options.semicolon === false && !options.prettier) {
 		if (options.ts) {
-			config.baseConfig.rules['@typescript-eslint/semi'] = ['error', 'never'];
+			config.baseConfig.rules['@typescript-eslint/semi'] ??= ['error', 'never'];
 		} else {
-			config.baseConfig.rules.semi = ['error', 'never'];
+			config.baseConfig.rules.semi ??= ['error', 'never'];
 		}
 
-		config.baseConfig.rules['semi-spacing'] = ['error', {
+		config.baseConfig.rules['semi-spacing'] ??= ['error', {
 			before: false,
 			after: true,
 		}];
 	}
 
 	if (options.ts) {
-		config.baseConfig.rules['unicorn/import-style'] = 'off';
-		config.baseConfig.rules['node/file-extension-in-import'] = 'off';
+		config.baseConfig.rules['unicorn/import-style'] ??= 'off';
+		config.baseConfig.rules['node/file-extension-in-import'] ??= 'off';
 
 		// Disabled because of https://github.com/benmosher/eslint-plugin-import/issues/1590
-		config.baseConfig.rules['import/export'] = 'off';
+		config.baseConfig.rules['import/export'] ??= 'off';
 
 		// Does not work when the TS definition exports a default const.
-		config.baseConfig.rules['import/default'] = 'off';
+		config.baseConfig.rules['import/default'] ??= 'off';
 
 		// Disabled as it doesn't work with TypeScript.
 		// This issue and some others: https://github.com/benmosher/eslint-plugin-import/issues/1341
-		config.baseConfig.rules['import/named'] = 'off';
+		config.baseConfig.rules['import/named'] ??= 'off';
 	}
 
 	config.baseConfig.settings['import/resolver'] = gatherImportResolvers(options);
@@ -444,7 +444,7 @@ const buildPrettierConfig = (options, prettierConfig) => config => {
 		config.baseConfig.extends.push('plugin:prettier/recommended');
 
 		// The `prettier/prettier` rule reports errors if the code is not formatted in accordance to Prettier
-		config.baseConfig.rules['prettier/prettier'] = ['error', mergeWithPrettierConfig(options, prettierConfig)];
+		config.baseConfig.rules['prettier/prettier'] ??= ['error', mergeWithPrettierConfig(options, prettierConfig)];
 	}
 
 	return config;

test/cli.js

@@ -197,3 +197,29 @@ test('print-config flag without filename', async t => {
 	);
 	t.is(error.stderr.trim(), 'The `--print-config` flag must be used with exactly one filename');
 });
+
+test('Do not override user-config', async t => {
+	const cwd = path.join(__dirname, 'fixtures/no-override-user-config');
+	const {stdout} = await main(['--print-config', 'index.js'], {cwd});
+	const config = JSON.parse(stdout);
+	t.like(config, {
+		rules: {
+			'n/no-unsupported-features/es-builtins': ['off'],
+			'n/no-unsupported-features/es-syntax': ['off'],
+			'n/no-unsupported-features/node-builtins': ['off'],
+		},
+	});
+
+	const {stdout: stdoutOverrides} = await main(['--print-config', 'overrides.js'], {cwd});
+	const configOverrides = JSON.parse(stdoutOverrides);
+	t.like(configOverrides, {
+		rules: {
+			'n/no-unsupported-features/es-builtins': ['off'],
+			'n/no-unsupported-features/es-syntax': ['off'],
+			'n/no-unsupported-features/node-builtins': ['error'],
+		},
+	});
+
+	await t.notThrowsAsync(() => main(['index.js'], {cwd}));
+	await t.throwsAsync(() => main(['overrides.js'], {cwd}));
+});

test/fixtures/no-override-user-config/index.js

@@ -0,0 +1 @@
+const _ = new FormData();

test/fixtures/no-override-user-config/overrides.js

@@ -0,0 +1 @@
+const _ = new FormData();

test/fixtures/no-override-user-config/package.json

@@ -0,0 +1,20 @@
+{
+	"xo": {
+		"rules": {
+			"n/no-unsupported-features/es-builtins": "off",
+			"n/no-unsupported-features/es-syntax": "off",
+			"n/no-unsupported-features/node-builtins": "off"
+		},
+		"overrides": [
+			{
+				"files": "overrides.js",
+				"rules": {
+					"n/no-unsupported-features/node-builtins": "error"
+				}
+			}
+		]
+	},
+	"engines": {
+		"node": ">=18"
+	}
+}