added support for customizing Browserslist discovery

passing `resolvePath` through several layers is awkward, but seemingly
inevitable (cf. b2bde4f)

Author: FND

lib/bundle/config.js

@@ -2,6 +2,7 @@
 
 let generateTranspiler = require("./babel");
 let { requireOptional } = require("../util");
+let determineBrowserslist = require("faucet-pipeline/lib/util/browserslist");
 let commonjs = require("rollup-plugin-commonjs");
 let nodeResolve = require("rollup-plugin-node-resolve");
 
@@ -24,7 +25,8 @@ module.exports = generateConfig;
 //   exports (if any)
 // * `esnext`, if truthy, activates ESNext transpilation
 //     * `esnext.browserslist`, if `false`, suppresses automatic configuration
-//       via Browserslist
+//       via Browserslist - alternatively, a path to a directory containing a
+//       custom Browserslist configuration
 //     * `esnext.exclude` is a list of modules for which to skip transpilation
 //       (e.g. `esnext: { exclude: ["jquery"] }`, perhaps due to a distribution
 //       already optimized for ES5)
@@ -37,7 +39,8 @@ module.exports = generateConfig;
 // * `compact`, if truthy, compresses the bundle's code while retaining the
 //   source code's original structure
 function generateConfig({ extensions = [], // eslint-disable-next-line indent
-		externals, format, moduleName, esnext, jsx, typescript, compact }, { browsers }) {
+		externals, format, moduleName, esnext, jsx, typescript, compact },
+		{ browsers, resolvePath }) {
 	let plugins = [];
 	if(esnext || jsx) {
 		let transpiler = Object.assign({}, esnext, jsx);
@@ -48,8 +51,16 @@ function generateConfig({ extensions = [], // eslint-disable-next-line indent
 			delete transpiler.pragma; // just to be safe, clean up JSX-specifics
 			transpiler.jsx = jsx;
 		}
-		if(transpiler.browserslist === false) { // TODO: support for custom path
+
+		let { browserslist } = transpiler
+		if(browserslist === false) {
 			browsers = null;
+		} else if(browserslist) {
+			let dir = resolvePath(browserslist, { enforceRelative: true });
+			browsers = determineBrowserslist(dir);
+			if(!browsers) {
+				throw new Error(`failed to detect Browserslist in ${browserslist}`);
+			}
 		}
 
 		let { plugin, extensions: ext } = generateTranspiler(transpiler, { browsers });

lib/bundle/index.js

@@ -10,12 +10,12 @@ let DEFAULTS = {
 };
 
 module.exports = class Bundle {
-	constructor(entryPoint, target, config, { browsers }) {
+	constructor(entryPoint, target, config, { browsers, resolvePath }) {
 		this.entryPoint = entryPoint;
 		this.target = target;
 
 		config = Object.assign({}, DEFAULTS, config);
-		this._config = generateConfig(config, { browsers });
+		this._config = generateConfig(config, { browsers, resolvePath });
 	}
 
 	// recompiles the bundle if its dependency graph includes any of the given files

lib/index.js

@@ -41,7 +41,7 @@ function makeBundle(config, resolvePath, { browsers }) {
 
 	entryPoint = resolvePath(entryPoint);
 	target = resolvePath(target, { enforceRelative: true });
-	return new Bundle(entryPoint, target, config, { browsers });
+	return new Bundle(entryPoint, target, config, { browsers, resolvePath });
 }
 
 // removes properties from object, returning their respective values

package.json

@@ -1,6 +1,6 @@
 {
 	"name": "faucet-pipeline-js",
-	"version": "1.0.0-beta.0",
+	"version": "1.0.0-beta.1",
 	"description": "JavaScript module bundling for faucet-pipeline",
 	"author": "FND",
 	"contributors": [
@@ -26,9 +26,9 @@
 		"node": ">=6"
 	},
 	"dependencies": {
-		"faucet-pipeline": "1.0.0-beta.0",
+		"faucet-pipeline": "1.0.0-beta.1",
 		"mkdirp": "^0.5.1",
-		"rollup": "^0.56.1",
+		"rollup": "^0.56.2",
 		"rollup-plugin-commonjs": "^8.3.0",
 		"rollup-plugin-node-resolve": "^3.0.3"
 	},
@@ -40,6 +40,6 @@
 		"json-diff": "^0.5.2",
 		"mocha": "^5.0.1",
 		"npm-run-all": "^4.1.2",
-		"release-util-fnd": "^1.0.7"
+		"release-util-fnd": "^1.1.0"
 	}
 }

test/unit/fixtures/alt/.browserslistrc

@@ -0,0 +1 @@
+Chrome 63

test/unit/test_bundling.js

@@ -268,6 +268,29 @@ console.log("[\\u2026] " + util); // eslint-disable-line no-console
 			});
 	});
 
+	it("should allow specifying an alternative Browserslist directory", () => {
+		let config = [{
+			source: "./src/index.js",
+			target: "./dist/bundle.js",
+			esnext: {
+				browserslist: "./alt"
+			}
+		}];
+		let assetManager = new MockAssetManager(FIXTURES_DIR);
+
+		return faucetJS(config, assetManager, { browsers: ["IE 11"] }).
+			then(_ => {
+				assetManager.assertWrites([{
+					filepath: path.resolve(FIXTURES_DIR, "./dist/bundle.js"),
+					content: makeBundle(`
+var util = "UTIL";
+
+console.log(\`[…] $\{util}\`); // eslint-disable-line no-console
+					`.trim())
+				}]);
+			});
+	});
+
 	it("should optionally compact bundle", () => {
 		let config = [{
 			source: "./src/index.js",