builders: webpack: cache input file state and only rebuild when needing to

resources/[system]/[builders]/webpack/webpack_runner.js

@@ -1,5 +1,48 @@
 const weebpack = require('webpack');
 const path = require('path');
+const fs = require('fs');
+
+function getStat(path) {
+	try {
+		const stat = fs.statSync(path);
+
+		return stat ? {
+			mtime: stat.mtimeMs,
+			size: stat.size,
+			inode: stat.ino,
+		} : null;
+	} catch {
+		return null;
+	}
+}
+
+class SaveStatePlugin {
+	constructor(inp) {
+		this.cache = [];
+		this.cachePath = inp.cachePath;
+	}
+
+	apply(compiler) {
+		compiler.hooks.afterCompile.tap('SaveStatePlugin', (compilation) => {
+			for (const file of compilation.fileDependencies) {
+				this.cache.push({
+					name: file,
+					stats: getStat(file)
+				});
+			}
+		});
+
+		compiler.hooks.done.tap('SaveStatePlugin', (stats) => {
+			if (stats.hasErrors()) {
+				return;
+			}
+
+			fs.writeFile(this.cachePath, JSON.stringify(this.cache), () => {
+
+			});
+		});
+	}
+}
 
 module.exports = (inp, callback) => {
 	const config = require(inp.configPath);
@@ -9,6 +52,12 @@ module.exports = (inp, callback) => {
 	if (config.output && config.output.path) {
 		config.output.path = path.resolve(inp.resourcePath, config.output.path);
 	}
+
+	if (!config.plugins) {
+		config.plugins = [];
+	}
+
+	config.plugins.push(new SaveStatePlugin(inp));
 	
 	weebpack(config, (err, stats) => {
 		if (err) {