Fix parent XO config resolution from nested package cwd

lib/resolve-config.ts

@@ -24,9 +24,8 @@ export async function resolveXoConfig(options: LinterOptions): Promise<{
 			options.cwd = path.resolve(process.cwd(), options.cwd);
 		}
 
-		const stopDirectory = path.dirname(options.cwd);
-
 		const flatConfigExplorer = cosmiconfig(moduleName, {
+			searchStrategy: 'project',
 			searchPlaces: [
 				'package.json',
 				`${moduleName}.config.js`,
@@ -38,7 +37,6 @@ export async function resolveXoConfig(options: LinterOptions): Promise<{
 				'.ts': loadTypeScriptConfig, // eslint-disable-line @typescript-eslint/naming-convention
 				'.mts': loadTypeScriptConfig, // eslint-disable-line @typescript-eslint/naming-convention
 			},
-			stopDir: stopDirectory,
 			cache: true,
 		});
 

lib/utils.ts

@@ -12,13 +12,6 @@ import {
 
 export {typescriptParser}; // eslint-disable-line unicorn/prefer-export-from -- Also used locally
 
-type TypeScriptParserOptions = Linter.ParserOptions & {
-	project?: string | string[];
-	projectService?: boolean;
-	tsconfigRootDir?: string;
-	programs?: unknown[];
-};
-
 /**
 Convert a `xo` config item to an ESLint config item.
 
@@ -87,6 +80,8 @@ const legacyPropertyHints: Record<string, string> = {
 	ignorePatterns: 'Use `ignores` instead.',
 };
 
+const isObjectRecord = (value: unknown): value is Record<string, unknown> => typeof value === 'object' && value !== null;
+
 /**
 Validate an XO config array for legacy ESLint config properties that are not supported in flat config.
 
@@ -123,17 +118,17 @@ export const preProcessXoConfig = (xoConfig: XoConfigItem[]): {config: XoConfigI
 	const processedConfig: XoConfigItem[] = xoConfig[0] ? [{...xoConfig[0]}] : [];
 
 	for (const {...config} of xoConfig.values().drop(1)) {
-		const languageOptions = config.languageOptions as Linter.LanguageOptions | undefined;
-		const parserOptions = languageOptions?.parserOptions as TypeScriptParserOptions | undefined;
+		const {languageOptions} = config;
+		const parserOptionsCandidate = languageOptions?.['parserOptions'];
+		const parserOptions = isObjectRecord(parserOptionsCandidate) ? parserOptionsCandidate : undefined;
 
 		// Use TS parser/plugin for JS files if the config contains TypeScript rules which are applied to JS files.
 		// typescript-eslint rules set to "off" are ignored and not applied to JS files.
 		if (
 			config.rules
-			// eslint-disable-next-line @typescript-eslint/dot-notation
 			&& !languageOptions?.['parser']
-			&& parserOptions?.project === undefined
-			&& parserOptions?.programs === undefined
+			&& parserOptions?.['project'] === undefined
+			&& parserOptions?.['programs'] === undefined
 			&& !config.plugins?.['@typescript-eslint']
 		) {
 			const hasTsRules = Object.entries(config.rules).some(rulePair => {
@@ -177,10 +172,10 @@ export const preProcessXoConfig = (xoConfig: XoConfigItem[]): {config: XoConfigI
 		}
 
 		// If the config sets `parserOptions.project`, `projectService`, `tsconfigRootDir`, or `programs`, treat those files as opt-out for XO's automatic program wiring.
-		if (parserOptions?.project !== undefined
-			|| parserOptions?.projectService !== undefined
-			|| parserOptions?.tsconfigRootDir !== undefined
-			|| parserOptions?.programs !== undefined) {
+		if (parserOptions?.['project'] !== undefined
+			|| parserOptions?.['projectService'] !== undefined
+			|| parserOptions?.['tsconfigRootDir'] !== undefined
+			|| parserOptions?.['programs'] !== undefined) {
 			// The glob itself should NOT be negated
 			tsFilesIgnoresGlob.push(...arrify(config.files ?? allFilesGlob).flat());
 		}

lib/xo.ts

@@ -76,6 +76,8 @@ const normalizeGlobPath = (filePath: string): string => filePath.split(path.sep)
 
 const pathMatchesPattern = (filePath: string, pattern: string): boolean => micromatch.isMatch(normalizeGlobPath(filePath), normalizeGlobPath(pattern), {dot: true});
 
+const isObjectRecord = (value: unknown): value is Record<string, unknown> => typeof value === 'object' && value !== null;
+
 const isIgnoredByPatterns = (filePath: string, patterns: string[]): boolean => {
 	let ignored = false;
 
@@ -669,9 +671,8 @@ export class Xo {
 			const tsconfigPath = path.join(this._cacheLocation, 'tsconfig.stdin.json');
 			const configIndex = this._xoConfig.findIndex(configItem => {
 				const {languageOptions} = configItem;
-				const parserOptionsCandidate = (languageOptions as Linter.LanguageOptions | undefined)?.parserOptions;
-				const parserOptions = parserOptionsCandidate as TypeScriptParserOptions | undefined;
-				return parserOptions?.project === tsconfigPath;
+				const parserOptionsCandidate = languageOptions?.['parserOptions'];
+				return isObjectRecord(parserOptionsCandidate) && parserOptionsCandidate['project'] === tsconfigPath;
 			});
 
 			if (nextVirtualFiles.size > 0) {

test/resolve-config.test.ts

@@ -110,6 +110,36 @@ test('resolves package.json object config', async t => {
 	t.deepEqual(flatOptions, [{space: true}]);
 });
 
+test('resolves parent package.json config from nested package cwd', async t => {
+	const pkg = JSON.parse(await fs.readFile(
+		path.join(t.context.cwd, 'package.json'),
+		'utf8',
+	)) as PackageJson;
+
+	pkg['xo'] = {space: true};
+
+	await fs.writeFile(
+		path.join(t.context.cwd, 'package.json'),
+		JSON.stringify(pkg),
+		'utf8',
+	);
+
+	const packageCwd = path.join(t.context.cwd, 'packages', 'app');
+	await fs.mkdir(packageCwd, {recursive: true});
+	await fs.writeFile(
+		path.join(packageCwd, 'package.json'),
+		JSON.stringify({name: 'app'}),
+		'utf8',
+	);
+
+	const {flatOptions, flatConfigPath} = await resolveXoConfig({
+		cwd: packageCwd,
+	});
+
+	t.deepEqual(flatConfigPath, path.join(t.context.cwd, 'package.json'));
+	t.deepEqual(flatOptions, [{space: true}]);
+});
+
 test('resolves all config extensions types', async t => {
 	const testConfigEsm = `export default [
 		{