system: add yarn builder resource

resources/[system]/[builders]/yarn/__resource.lua

@@ -0,0 +1,2 @@
+server_only 'yes'
+server_script 'yarn_builder.js'

resources/[system]/[builders]/yarn/yarn_builder.js

@@ -0,0 +1,53 @@
+const path = require('path');
+const fs = require('fs');
+const child_process = require('child_process');
+
+const yarnBuildTask = {
+	shouldBuild(resourceName) {
+		try {
+			const resourcePath = GetResourcePath(resourceName);
+			
+			const packageJson = path.resolve(resourcePath, 'package.json');
+			const yarnLock = path.resolve(resourcePath, 'yarn.lock');
+			
+			const packageStat = fs.statSync(packageJson);
+			
+			try {
+				const yarnStat = fs.statSync(yarnLock);
+			
+				if (packageStat.mtimeMs > yarnStat.mtimeMs) {
+					return true;
+				}
+			} catch (e) {
+				// no yarn.lock, but package.json - install time!
+				return true;
+			}
+		} catch (e) {
+			
+		}
+		
+		return false;
+	},
+	
+	build(resourceName, cb) {
+		const process = child_process.fork(
+			require.resolve('./yarn_cli.js'),
+			['install'],
+			{
+				cwd: path.resolve(GetResourcePath(resourceName))
+			});
+			
+		process.on('exit', (code, signal) => {
+			setImmediate(() => {
+				if (code != 0 || signal) {
+					cb(false, 'yarn failed!');
+					return;
+				}
+			
+				cb(true);
+			});
+		});
+	}
+}
+
+RegisterResourceBuildTaskFactory('yarn', () => yarnBuildTask);