Map provider protocols to 'levels'

Rather than perform typeof checks to see if the provider has a
particular feature, check the 'support level' instead. This should make
code using a provider easier to maintain.

eslint-plugin-helper.js

@@ -22,16 +22,20 @@ function load(projectDir, overrides) {
 
 		providers = [];
 		if (Reflect.has(conf, 'babel')) {
+			const {level, main} = providerManager.babel(projectDir);
 			providers.push({
-				type: 'babel',
-				main: providerManager.babel(projectDir).main({config: conf.babel})
+				level,
+				main: main({config: conf.babel}),
+				type: 'babel'
 			});
 		}
 
 		if (Reflect.has(conf, 'typescript')) {
+			const {level, main} = providerManager.typescript(projectDir);
 			providers.push({
-				type: 'typescript',
-				main: providerManager.typescript(projectDir).main({config: conf.typescript})
+				level,
+				main: main({config: conf.typescript}),
+				type: 'typescript'
 			});
 		}
 

lib/cli.js

@@ -282,9 +282,11 @@ exports.run = async () => { // eslint-disable-line complexity
 	const providers = [];
 	if (Reflect.has(conf, 'babel')) {
 		try {
+			const {level, main} = providerManager.babel(projectDir);
 			providers.push({
-				type: 'babel',
-				main: providerManager.babel(projectDir).main({config: conf.babel})
+				level,
+				main: main({config: conf.babel}),
+				type: 'babel'
 			});
 		} catch (error) {
 			exit(error.message);
@@ -293,9 +295,11 @@ exports.run = async () => { // eslint-disable-line complexity
 
 	if (Reflect.has(conf, 'typescript')) {
 		try {
+			const {level, main} = providerManager.typescript(projectDir);
 			providers.push({
-				type: 'typescript',
-				main: providerManager.typescript(projectDir).main({config: conf.typescript})
+				level,
+				main: main({config: conf.typescript}),
+				type: 'typescript'
 			});
 		} catch (error) {
 			exit(error.message);

lib/provider-manager.js

@@ -1,24 +1,39 @@
 const pkg = require('../package.json');
 const globs = require('./globs');
 
+const levels = {
+	ava3: 1
+};
+
+exports.levels = levels;
+
+const levelsByProtocol = {
+	'ava-3': levels.ava3
+};
+
 function load(providerModule, projectDir) {
 	const ava = {version: pkg.version};
 	const makeProvider = require(providerModule);
 
 	let fatal;
+	let level;
 	const provider = makeProvider({
 		negotiateProtocol(identifiers, {version}) {
-			if (!identifiers.includes('ava-3')) {
+			const [identifier] = identifiers.filter(identifier => Reflect.has(levelsByProtocol, identifier));
+
+			if (identifier === undefined) {
 				fatal = new Error(`This version of AVA (${ava.version}) is not compatible with ${providerModule}@${version}`);
 				return null;
 			}
 
+			level = levelsByProtocol[identifier];
+
 			return {
 				ava,
 				async findFiles({extensions, patterns}) {
 					return globs.findFiles({cwd: projectDir, extensions, filePatterns: patterns});
 				},
-				identifier: 'ava-3',
+				identifier,
 				normalizeGlobPatterns: globs.normalizePatterns,
 				projectDir
 			};
@@ -29,7 +44,7 @@ function load(providerModule, projectDir) {
 		throw fatal;
 	}
 
-	return provider;
+	return {...provider, level};
 }
 
 exports.babel = projectDir => load('@ava/babel', projectDir);