@@ -52,3 +52,4 @@ packages/**/*.map
 
 # temporary test files
 test-assets/
+./lib/
@@ -0,0 +1,15 @@
+'use strict';
+
+// eslint-disable-next-line node/no-unpublished-require
+const { run } = require('../../utils/test-utils');
+
+describe('loader error regression test for #1581', () => {
+    it(`should not ignore loader's error produce a failing build`, () => {
+        // Ignoring assertion on stderr because ts-loader is producing depreciation warnings
+        // with webpack@v5.0.0-beta.24 -> https://github.com/TypeStrong/ts-loader/issues/1169
+        const { stdout } = run(__dirname, [], false);
+
+        expect(stdout).toContain('[1 error]');
+        expect(stdout).toContain(`Cannot assign to 'foobar' because it is a constant`);
+    });
+});
@@ -0,0 +1,6 @@
+{
+  "dependencies": {
+    "ts-loader": "^7.0.5",
+    "typescript": "^3.9.3"
+  }
+}
@@ -0,0 +1,4 @@
+const foobar = 'foobar';
+// eslint-disable-next-line no-const-assign
+foobar = 'barbaz'; // Error!
+console.log(foobar);
@@ -0,0 +1,25 @@
+const path = require('path');
+
+module.exports = {
+    mode: 'development',
+
+    entry: {
+        bundle: './src/index.ts',
+    },
+
+    output: {
+        path: path.resolve(__dirname, 'dist'),
+        filename: '[name].js',
+    },
+
+    module: {
+        rules: [
+            {
+                test: /.(ts|tsx)?$/,
+                loader: 'ts-loader',
+                include: [path.resolve(__dirname, 'src')],
+                exclude: [/node_modules/],
+            },
+        ],
+    },
+};
Original file line number	Diff line number	Diff line change
`@@ -52,3 +52,4 @@ packages/*/.map`
`52`	`52`
`53`	`53`	`# temporary test files`
`54`	`54`	`test-assets/`
	`55`	`+./lib/`