tests: add tests in case of warnings from loader

packages/webpack-cli/lib/utils/Compiler.js

@@ -80,7 +80,7 @@ class Compiler {
             logger.error(err.stack || err);
             process.exit(1); // eslint-disable-line
         }
-        if (!outputOptions.watch && stats.hasErrors()) {
+        if (!outputOptions.watch && (stats.hasErrors() || stats.hasWarnings())) {
             process.exitCode = 1;
         }
         if (outputOptions.json) {

test/loader/warning-test/dist/bundle.js

@@ -0,0 +1,17 @@
+/*
+ * ATTENTION: The "eval" devtool has been used (maybe by default in mode: "development").
+ * This devtool is not neither made for production nor for readable output files.
+ * It uses "eval()" calls to create a separate source file in the browser devtools.
+ * If you are trying to read the output file, select a different devtool (https://webpack.js.org/configuration/devtool/)
+ * or disable the default devtool with "devtool: false".
+ * If you are looking for production-ready output files, see mode: "production" (https://webpack.js.org/configuration/mode/).
+ */
+/******/ (() => { // webpackBootstrap
+/*!*********************!*\
+  !*** ./src/main.js ***!
+  \*********************/
+/*! unknown exports (runtime-defined) */
+/*! runtime requirements:  */
+eval("console.log('loader warning test');\n\n\n//# sourceURL=webpack:///./src/main.js?");
+/******/ })()
+;

test/loader/warning-test/loader-warning.test.js

@@ -0,0 +1,12 @@
+'use strict';
+
+const { run } = require('../../utils/test-utils');
+
+describe('loader warning test', () => {
+    it(`should not ignore loader's warning and exit with a non zero exit code`, () => {
+        const { stdout, exitCode } = run(__dirname, [], false);
+
+        expect(stdout).toContain('This is a warning');
+        expect(exitCode).not.toEqual(0);
+    });
+});

test/loader/warning-test/my-loader.js

@@ -0,0 +1,5 @@
+module.exports = function loader(source) {
+    const { emitWarning } = this;
+    emitWarning('This is a warning');
+    return source;
+};

test/loader/warning-test/src/main.js

@@ -0,0 +1 @@
+console.log('loader warning test');

test/loader/warning-test/webpack.config.js

@@ -0,0 +1,30 @@
+const path = require('path');
+
+module.exports = {
+    mode: 'development',
+
+    entry: {
+        bundle: './src/main.js',
+    },
+
+    output: {
+        path: path.resolve(__dirname, 'dist'),
+        filename: '[name].js',
+    },
+
+    module: {
+        rules: [
+            {
+                test: /.(js|jsx)?$/,
+                loader: 'my-loader',
+                include: [path.resolve(__dirname, 'src')],
+                exclude: [/node_modules/],
+            },
+        ],
+    },
+    resolveLoader: {
+        alias: {
+            'my-loader': require.resolve('./my-loader'),
+        },
+    },
+};