added tests for swallowed loader errors, fixed another swallowed error

Author: Steven Hargrove

lib/Compilation.js

@@ -931,6 +931,8 @@ class Compilation {
 							return callback(err);
 						}
 
+						if (module.error) return callback(module.error);
+
 						// This avoids deadlocks for circular dependencies
 						if (this.processDependenciesQueue.isProcessing(module)) {
 							return callback();
@@ -1067,14 +1069,12 @@ class Compilation {
 			},
 			err => {
 				if (this.bail) {
-					const result = callback(err);
-
+					callback(err);
 					this.buildQueue.stop();
 					this.rebuildQueue.stop();
 					this.processDependenciesQueue.stop();
 					this.factorizeQueue.stop();
-
-					return result;
+					return;
 				}
 				return callback();
 			}

test/Errors.test.js

@@ -304,6 +304,64 @@ describe("Errors", () => {
 					);
 				}
 			),
+			getErrorsPromise(
+				{
+					mode: "development",
+					entry: "./entry-point.js",
+					module: {
+						rules: [
+							{
+								test: /entry-point\.js$/,
+								use: path.resolve(base, "./doesnt-exist-loader")
+							}
+						]
+					}
+				},
+				(errors, warnings) => {
+					expect(errors).toHaveLength(1);
+					expect(errors[0]).toMatch(/^Module not found/);
+				}
+			),
+			getErrorsPromise(
+				{
+					mode: "development",
+					entry: "./entry-point.js",
+					module: {
+						rules: [
+							{
+								test: /entry-point\.js$/,
+								use: path.resolve(base, "./return-undefined-loader")
+							}
+						]
+					}
+				},
+				(errors, warnings) => {
+					expect(errors).toHaveLength(1);
+					expect(errors[0].split("\n")[1]).toMatch(
+						/^Module build failed: Error: Final loader \(\.\/return-undefined-loader\.js\) didn't return a Buffer or String$/
+					);
+				}
+			),
+			getErrorsPromise(
+				{
+					mode: "development",
+					entry: "./entry-point.js",
+					module: {
+						rules: [
+							{
+								test: /entry-point\.js$/,
+								use: path.resolve(base, "./module-exports-object-loader")
+							}
+						]
+					}
+				},
+				(errors, warnings) => {
+					expect(errors).toHaveLength(1);
+					expect(errors[0].split("\n")[1]).toMatch(
+						/^Module '.*\/module-exports-object-loader\.js' is not a loader \(must have normal or pitch function\)$/
+					);
+				}
+			),
 			getErrorsPromise(
 				{
 					mode: "development",

test/fixtures/errors/module-exports-object-loader.js

@@ -0,0 +1 @@
+module.exports = {};

test/fixtures/errors/return-undefined-loader.js

@@ -0,0 +1 @@
+module.exports = () => {};