Warn when unsupported ava.config.json files are encountered

lib/cli.js

@@ -104,7 +104,14 @@ export default async function loadCli() { // eslint-disable-line complexity
 	let confError;
 	try {
 		const {argv: {config: configFile}} = yargs(hideBin(process.argv)).help(false).version(false);
-		conf = await loadConfig({configFile});
+		const loaded = await loadConfig({configFile});
+		if (loaded.unsupportedFiles.length > 0) {
+			console.log(chalk.magenta(
+				`  ${figures.warning} AVA does not support JSON config, ignoring:\n\n    ${loaded.unsupportedFiles.join('\n    ')}`,
+			));
+		}
+
+		conf = loaded.config;
 		if (conf.configFile && path.basename(conf.configFile) !== path.relative(conf.projectDir, conf.configFile)) {
 			console.log(chalk.magenta(`  ${figures.warning} Using configuration from ${conf.configFile}`));
 		}

lib/eslint-plugin-helper-worker.js

@@ -41,7 +41,7 @@ const buildGlobs = ({conf, providers, projectDir, overrideExtensions, overrideFi
 
 const resolveGlobs = async (projectDir, overrideExtensions, overrideFiles) => {
 	if (!configCache.has(projectDir)) {
-		configCache.set(projectDir, loadConfig({resolveFrom: projectDir}).then(async conf => {
+		configCache.set(projectDir, loadConfig({resolveFrom: projectDir}).then(async ({config: conf}) => {
 			const providers = await collectProviders({conf, projectDir});
 			return {conf, providers};
 		}));

lib/load-config.js

@@ -20,14 +20,15 @@ const importConfig = async ({configFile, fileForErrorMessage}) => {
 };
 
 const loadConfigFile = async ({projectDir, configFile}) => {
-	if (!fs.existsSync(configFile)) {
-		return null;
-	}
-
 	const fileForErrorMessage = path.relative(projectDir, configFile);
 	try {
+		await fs.promises.access(configFile);
 		return {config: await importConfig({configFile, fileForErrorMessage}), configFile, fileForErrorMessage};
 	} catch (error) {
+		if (error.code === 'ENOENT') {
+			return null;
+		}
+
 		throw Object.assign(new Error(`Error loading ${fileForErrorMessage}: ${error.message}`), {parent: error});
 	}
 };
@@ -63,6 +64,20 @@ async function findRepoRoot(fromDir) {
 	return root;
 }
 
+async function checkJsonFile(searchDir) {
+	const file = path.join(searchDir, 'ava.config.json');
+	try {
+		await fs.promises.access(file);
+		return file;
+	} catch (error) {
+		if (error.code === 'ENOENT') {
+			return null;
+		}
+
+		throw error;
+	}
+}
+
 export async function loadConfig({configFile, resolveFrom = process.cwd(), defaults = {}} = {}) {
 	let packageConf = await packageConfig('ava', {cwd: resolveFrom});
 	const filepath = packageJsonPath(packageConf);
@@ -74,6 +89,7 @@ export async function loadConfig({configFile, resolveFrom = process.cwd(), defau
 	const allowConflictWithPackageJson = Boolean(configFile);
 	configFile = resolveConfigFile(configFile);
 
+	const unsupportedFiles = [];
 	let fileConf = NO_SUCH_FILE;
 	let fileForErrorMessage;
 	let conflicting = [];
@@ -86,12 +102,17 @@ export async function loadConfig({configFile, resolveFrom = process.cwd(), defau
 		let searchDir = projectDir;
 		const stopAt = path.dirname(repoRoot);
 		do {
-			const results = await Promise.all([ // eslint-disable-line no-await-in-loop
+			const [jsonFile, ...results] = await Promise.all([ // eslint-disable-line no-await-in-loop
+				checkJsonFile(searchDir),
 				loadConfigFile({projectDir, configFile: path.join(searchDir, 'ava.config.js')}),
 				loadConfigFile({projectDir, configFile: path.join(searchDir, 'ava.config.cjs')}),
 				loadConfigFile({projectDir, configFile: path.join(searchDir, 'ava.config.mjs')}),
 			]);
 
+			if (jsonFile !== null) {
+				unsupportedFiles.push(jsonFile);
+			}
+
 			[{config: fileConf, fileForErrorMessage, configFile} = {config: NO_SUCH_FILE, fileForErrorMessage: undefined}, ...conflicting] = results.filter(result => result !== null);
 
 			searchDir = path.dirname(searchDir);
@@ -139,5 +160,5 @@ export async function loadConfig({configFile, resolveFrom = process.cwd(), defau
 		}
 	}
 
-	return config;
+	return {config, unsupportedFiles};
 }

test/config/fixtures/unsupported-configs/ava.config.js

@@ -0,0 +1,3 @@
+export default {
+	failFast: true,
+};

test/config/fixtures/unsupported-configs/ava.config.json

@@ -0,0 +1 @@
+{}

test/config/fixtures/unsupported-configs/package.json

@@ -0,0 +1,3 @@
+{
+	"type": "module"
+}

test/config/loader.js

@@ -10,13 +10,15 @@ const FIXTURE_ROOT = fileURLToPath(new URL('../../test-tap/fixture/load-config',
 
 const resolve = relpath => path.resolve(FIXTURE_ROOT, relpath);
 
-const loadFromSetup = setup => {
+const loadFromSetup = async setup => {
 	if (typeof setup === 'string') {
-		return loadConfig();
+		const loaded = await loadConfig();
+		return loaded.config;
 	}
 
 	const {configFile, defaults, resolveFrom} = setup;
-	return loadConfig({configFile, defaults, resolveFrom});
+	const loaded = await loadConfig({configFile, defaults, resolveFrom});
+	return loaded.config;
 };
 
 const ok = setup => async (t, assert = tt => tt.pass()) => {

test/config/next-gen.js

@@ -10,23 +10,31 @@ const FIXTURE_ROOT = fileURLToPath(new URL('fixtures', import.meta.url));
 
 const resolve = relpath => path.resolve(FIXTURE_ROOT, relpath);
 
-const loadFromSetup = setup => {
+const loadFromSetup = async (setup, t, assertUnsupportedFiles = (tt, files) => tt.is(files.length, 0)) => {
 	if (typeof setup === 'string') {
-		return loadConfig();
+		const loaded = await loadConfig();
+		return loaded.config;
 	}
 
-	const {configFile, defaults, resolveFrom} = setup;
-	return loadConfig({configFile, defaults, resolveFrom});
+	const {
+		configFile,
+		defaults,
+		resolveFrom,
+	} = setup;
+
+	const loaded = await loadConfig({configFile, defaults, resolveFrom});
+	assertUnsupportedFiles(t, loaded.unsupportedFiles);
+	return loaded.config;
 };
 
-const ok = setup => async (t, assert = tt => tt.pass()) => {
+const ok = setup => async (t, assert = tt => tt.pass(), assertUnsupportedFiles = undefined) => {
 	const fixture = typeof setup === 'string' ? setup : setup.fixture;
 
 	const stub = sinon.stub(process, 'cwd');
 	t.teardown(() => stub.restore());
 	stub.returns(resolve(fixture));
 
-	const conf = loadFromSetup(setup);
+	const conf = loadFromSetup(setup, t, assertUnsupportedFiles);
 	await t.notThrowsAsync(conf);
 	const result = await t.try(assert, await conf, setup);
 	result.commit();
@@ -39,7 +47,7 @@ const notOk = setup => async (t, assert = (tt, error) => tt.snapshot(error.messa
 	t.teardown(() => stub.restore());
 	stub.returns(resolve(fixture));
 
-	const conf = loadFromSetup(setup);
+	const conf = loadFromSetup(setup, t);
 	const error = await t.throwsAsync(conf);
 	const result = await t.try(assert, error, setup);
 	result.commit();
@@ -67,6 +75,19 @@ test.serial('loads .js config as ESM', ok('js-as-esm'), (t, conf) => {
 	t.true(conf.failFast);
 });
 
+test.serial('finds unsupported configs',
+	ok({
+		fixture: 'unsupported-configs',
+	}),
+	(t, conf) => {
+		t.true(conf.failFast);
+	},
+	(t, unsupportedFiles) => {
+		t.is(unsupportedFiles.length, 1);
+		t.regex(unsupportedFiles[0], /ava\.config\.json/);
+	},
+);
+
 test.serial('handles errors when loading .js config as ESM', notOk({
 	fixture: 'js-as-esm',
 	configFile: 'error.js',