Merge pull request webpack#6467 from PlayMa256/prompt_install_cli

Prompt install cli

bin/webpack.js

@@ -1,21 +1,82 @@
 #!/usr/bin/env node
+function runCommand(command, options) {
+	const cp = require("child_process");
+	return new Promise((resolve, reject) => {
+		const executedCommand = cp.spawn(command, options, {
+			stdio: "inherit"
+		});
+
+		executedCommand.on("error", error => {
+			reject(error);
+		});
+
+		executedCommand.on("exit", code => {
+			if (code === 0) {
+				resolve(true);
+			} else {
+				reject();
+			}
+		});
+	});
+}
 
 let webpackCliInstalled = false;
 try {
 	require.resolve("webpack-cli");
 	webpackCliInstalled = true;
-} catch (e) {
+} catch (err) {
 	webpackCliInstalled = false;
 }
 
-if (webpackCliInstalled) {
-	require("webpack-cli"); // eslint-disable-line node/no-missing-require, node/no-extraneous-require, node/no-unpublished-require
+if (!webpackCliInstalled) {
+	const path = require("path");
+	const fs = require("fs");
+	const readLine = require("readline");
+	const isYarn = fs.existsSync(path.resolve(process.cwd(), "yarn.lock"));
+
+	const packageManager = isYarn ? "yarn" : "npm";
+	const options = ["install", "-D", "webpack-cli"];
+
+	if (isYarn) {
+		options[0] = "add";
+	}
+
+	const commandToBeRun = `${packageManager} ${options.join(" ")}`;
+
+	const question = `Would you like to install webpack-cli? (That will run ${
+		commandToBeRun
+	}) `;
+
+	console.error("The CLI moved into a separate package: webpack-cli");
+	const questionInterface = readLine.createInterface({
+		input: process.stdin,
+		output: process.stdout
+	});
+	questionInterface.question(question, answer => {
+		questionInterface.close();
+		switch (answer.toLowerCase()) {
+			case "y":
+			case "yes":
+			case "1": {
+				runCommand(packageManager, options)
+					.then(result => {
+						return require("webpack-cli"); //eslint-disable-line
+					})
+					.catch(error => {
+						console.error(error);
+						process.exitCode = 1;
+					});
+				break;
+			}
+			default: {
+				console.error(
+					"It needs to be installed alongside webpack to use the CLI"
+				);
+				process.exitCode = 1;
+				break;
+			}
+		}
+	});
 } else {
-	console.error("The CLI moved into a separate package: webpack-cli.");
-	console.error(
-		"Please install 'webpack-cli' in addition to webpack itself to use the CLI."
-	);
-	console.error("-> When using npm: npm install webpack-cli -D");
-	console.error("-> When using yarn: yarn add webpack-cli -D");
-	process.exitCode = 1;
+	require("webpack-cli"); // eslint-disable-line
 }