added experimental TypeScript support

caveats:
* special-casing (cf. inline comment) complicates `generateConfig`
* there's barely any abstraction here (cf. inline comment); why bother?
* `generateTranspilerConfig` now actually only takes care of Babel
  configuration, which is likely confusing; we'll probably wanna move
  these details into transpiler-specific modules
* no tests yet; these are essential for mainline integration
* this anticipates a faucet-pipeline-typescript meta-package
* the sample seems pretty silly

Co-authored-by: FND <fnd@localhost.localdomain>

.gitignore

@@ -1,4 +1,4 @@
 /node_modules
 /.eslintcache
 
-/samples/dist
+/samples/*/dist

lib/bundle/config.js

@@ -24,30 +24,40 @@ module.exports = generateConfig;
 // * `moduleName` determines the global variable to hold the entry point's
 //   exports (if any)
 // * `transpiler.features` determines the language features to be supported
-//   within source code (e.g. `["es2015", "jsx"]`)
+//   within source code (e.g. `["es2015", "typescript", "jsx"]`)
+// * `transpiler.typescript` are TypeScript-specific options
 // * `transpiler.jsx` are JSX-specific options (e.g. `{ pragma: "createElement" }`)
 // * `transpiler.exclude` is a list of modules for which to skip transpilation
 //   (e.g. `["jquery"]`, perhaps due to an already optimized ES5 distribution)
 function generateConfig({ extensions = [], // eslint-disable-next-line indent
 		externals, format, compact, moduleName, transpiler }) {
+	let plugins = [];
 	if(transpiler) {
-		let { features } = transpiler;
-		if(features && features.includes("jsx")) {
-			extensions = [".jsx"].concat(extensions);
-		}
+		let { features = [] } = transpiler;
+		if(features.includes("typescript")) { // XXX: special-casing
+			let ts = requireOptional("rollup-plugin-typescript2",
+					"failed to activate TypeScript", "faucet-pipeline-typescript");
+			// TODO: provide defaults and abstractions for low-level options
+			let { typescript } = transpiler;
+			plugins.push(typescript ? ts(typescript) : ts());
+		} else {
+			if(features.includes("jsx")) {
+				extensions = [".jsx"].concat(extensions);
+			}
 
-		let babel = requireOptional("rollup-plugin-babel",
-				"failed to activate transpiler", "faucet-pipeline-esnext");
-		let settings = generateTranspilerConfig(transpiler);
-		transpiler = babel(settings);
+			let babel = requireOptional("rollup-plugin-babel",
+					"failed to activate transpiler", "faucet-pipeline-esnext");
+			let settings = generateTranspilerConfig(transpiler);
+			plugins.push(babel(settings));
+		}
 	}
 
 	let resolve = { jsnext: true };
 	if(extensions.length) {
 		resolve.extensions = [".js"].concat(extensions);
 	}
 
-	let plugins = (transpiler ? [transpiler] : []).concat([
+	plugins = plugins.concat([
 		nodeResolve(resolve),
 		commonjs({ include: "node_modules/**" })
 	]);
@@ -81,7 +91,7 @@ function generateConfig({ extensions = [], // eslint-disable-next-line indent
 	});
 }
 
-function generateTranspilerConfig({ features, jsx = {}, exclude }) {
+function generateTranspilerConfig({ features, jsx, exclude }) {
 	let settings = {};
 	let plugins = [];
 
@@ -102,7 +112,7 @@ function generateTranspilerConfig({ features, jsx = {}, exclude }) {
 	}
 
 	if(features.includes("jsx")) {
-		plugins.push(["transform-react-jsx", jsx]);
+		plugins.push(["transform-react-jsx", jsx || {}]);
 	}
 
 	if(plugins.length) {

samples/faucet.config.js → samples/esnext/faucet.config.js

@@ -1,3 +1,5 @@
+"use strict";
+
 module.exports = {
 	manifest: {
 		file: "./dist/manifest.json"

samples/typescript/faucet.config.js

@@ -0,0 +1,11 @@
+"use strict";
+
+module.exports = {
+	js: [{
+		source: "./index.ts",
+		target: "./dist/bundle.js",
+		transpiler: {
+			features: ["typescript"]
+		}
+	}]
+};

samples/typescript/index.ts

@@ -0,0 +1,28 @@
+import { log, LogLevel } from "./util";
+
+interface ComplexTitle {
+	main: string;
+	sub: string;
+}
+
+interface ArticleInterface {
+	title: string | ComplexTitle;
+	authors: string[];
+}
+
+let generateArticle = (params: ArticleInterface) => {
+	let { title, authors } = params;
+	if(typeof title !== "string") {
+		log(LogLevel.Debug, "auto-generating title");
+		title = `${title.main}: ${title.sub}`;
+	}
+	return title + "\n" + authors.join(", ");
+};
+
+generateArticle({
+	title: {
+		main: "Hello World",
+		sub: "sup"
+	},
+	authors: ["foo", "bar"]
+});

samples/typescript/util.ts

@@ -0,0 +1,9 @@
+export enum LogLevel { Debug, Info, Critical }
+
+export function log(level: LogLevel, msg: string) {
+	if(level === LogLevel.Critical) {
+		console.error(msg);
+	} else {
+		console.log(msg);
+	}
+}