make multiple assets to the same filename a warning

check source content to when comparing assets for warning

lib/Compilation.js

@@ -37,11 +37,11 @@ const compareLocations = require("./compareLocations");
 const { Logger, LogType } = require("./logging/Logger");
 const ErrorHelpers = require("./ErrorHelpers");
 const buildChunkGraph = require("./buildChunkGraph");
+const WebpackError = require("./WebpackError");
 
 /** @typedef {import("./Module")} Module */
 /** @typedef {import("./Compiler")} Compiler */
 /** @typedef {import("webpack-sources").Source} Source */
-/** @typedef {import("./WebpackError")} WebpackError */
 /** @typedef {import("./DependenciesBlockVariable")} DependenciesBlockVariable */
 /** @typedef {import("./dependencies/SingleEntryDependency")} SingleEntryDependency */
 /** @typedef {import("./dependencies/MultiEntryDependency")} MultiEntryDependency */
@@ -221,6 +221,25 @@ const addAllToSet = (set, otherSet) => {
 	}
 };
 
+/**
+ * @param {Source} a a source
+ * @param {Source} b another source
+ * @returns {boolean} true, when both sources are equal
+ */
+const isSourceEqual = (a, b) => {
+	if (a === b) return true;
+	// TODO webpack 5: check .buffer() instead, it's called anyway during emit
+	/** @type {Buffer|string} */
+	let aSource = a.source();
+	/** @type {Buffer|string} */
+	let bSource = b.source();
+	if (aSource === bSource) return true;
+	if (typeof aSource === "string" && typeof bSource === "string") return false;
+	if (!Buffer.isBuffer(aSource)) aSource = Buffer.from(aSource, "utf-8");
+	if (!Buffer.isBuffer(bSource)) bSource = Buffer.from(bSource, "utf-8");
+	return aSource.equals(bSource);
+};
+
 class Compilation extends Tapable {
 	/**
 	 * Creates an instance of Compilation.
@@ -1990,10 +2009,16 @@ class Compilation extends Tapable {
 	 */
 	emitAsset(file, source, assetInfo = {}) {
 		if (this.assets[file]) {
-			if (this.assets[file] !== source) {
-				throw new Error(
-					`Conflict: Multiple assets emit to the same filename ${file}`
+			if (!isSourceEqual(this.assets[file], source)) {
+				// TODO webpack 5: make this an error instead
+				this.warnings.push(
+					new WebpackError(
+						`Conflict: Multiple assets emit different content to the same filename ${file}`
+					)
 				);
+				this.assets[file] = source;
+				this.assetsInfo.set(file, assetInfo);
+				return;
 			}
 			const oldInfo = this.assetsInfo.get(file);
 			this.assetsInfo.set(file, Object.assign({}, oldInfo, assetInfo));

test/configCases/emit-asset/different-source/index.js

@@ -0,0 +1,4 @@
+it("should compile without warnings", () => {
+	require("./test1.txt");
+	require("./test2.txt");
+});

test/configCases/emit-asset/different-source/test1.txt

@@ -0,0 +1 @@
+Hello World

test/configCases/emit-asset/different-source/test2.txt

@@ -0,0 +1 @@
+Something else

test/configCases/emit-asset/different-source/warnings.js

@@ -0,0 +1,7 @@
+module.exports = [
+	[
+		/Conflict/,
+		/Multiple assets emit different content to the same filename/,
+		/same-name\.txt/
+	]
+];

test/configCases/emit-asset/different-source/webpack.config.js

@@ -0,0 +1,15 @@
+module.exports = {
+	module: {
+		rules: [
+			{
+				test: /\.txt$/,
+				use: {
+					loader: "file-loader",
+					options: {
+						name: "same-name.txt"
+					}
+				}
+			}
+		]
+	}
+};

test/configCases/emit-asset/equal-source/index.js

@@ -0,0 +1,4 @@
+it("should compile without warnings", () => {
+	require("./test1.txt");
+	require("./test2.txt");
+});

test/configCases/emit-asset/equal-source/test1.txt

@@ -0,0 +1 @@
+Hello World

test/configCases/emit-asset/equal-source/test2.txt

@@ -0,0 +1 @@
+Hello World

test/configCases/emit-asset/equal-source/webpack.config.js

@@ -0,0 +1,15 @@
+module.exports = {
+	module: {
+		rules: [
+			{
+				test: /\.txt$/,
+				use: {
+					loader: "file-loader",
+					options: {
+						name: "same-name.txt"
+					}
+				}
+			}
+		]
+	}
+};