feat: Allow use of error object inside the notifier message/title

Related to micromata#7

lib/error-notifier.js

@@ -3,12 +3,65 @@ const notifier = require('node-notifier');
 
 const notifierOptions = require('./notifier-options');
 
+const errorLiteral = 'error';
+
+function errorLiteralPosition(str) {
+	let index = str.indexOf(`\${${errorLiteral}`);
+	let length = 0;
+
+	if (index > -1) {
+		index += 2;
+
+		let open = 1;
+
+		while (length < str.length - index) {
+			const char = str.charAt(index + length);
+
+			if (char === '{') {
+				open++;
+			} else if (char === '}') {
+				open--;
+			}
+
+			if (open === 0) {
+				break;
+			}
+
+			length++;
+		}
+
+		if (open > 0) {
+			throw new TypeError('Missing brace for error literal!');
+		}
+	}
+
+	return {index, length};
+}
+
+function errorLiteralReplace(err, msg) {
+	let position;
+
+	while ((position = errorLiteralPosition(msg)) && position.index > -1) {
+		const lc = msg.substr(position.index, position.length);
+		const fn = new Function(errorLiteral, `return ${lc}`); // eslint-disable-line no-new-func
+		msg = msg.replace(`\${${lc}}`, fn(err));
+	}
+
+	return msg;
+}
+
 module.exports = (command, opts) => {
 	opts = opts || {};
 
 	return new Promise((resolve, reject) => {
 		execa.shell(command, {env: {FORCE_COLOR: true}})
 			.then(result => resolve(result))
-			.catch(err => notifier.notify(notifierOptions(opts), () => reject(err)));
+			.catch(err => {
+				const notifierOpts = notifierOptions(opts);
+				notifierOpts.title = errorLiteralReplace(err, notifierOpts.title);
+				notifierOpts.message = errorLiteralReplace(err, notifierOpts.message);
+
+				return notifier.notify(notifierOpts, () => reject(err));
+			});
 	});
 };