fix #7829

webpack-hot-client seem to call `addEntry` multiple
which causes two Entrypoints with the same name
This lead the bad side effects
i. e. optimization.runtimeChunk no longer works correctly

Now adding an entry with the same name replaces the existing entry

lib/Compilation.js

@@ -1025,6 +1025,7 @@ class Compilation extends Tapable {
 	addEntry(context, entry, name, callback) {
 		const slot = {
 			name: name,
+			// TODO webpack 5 remove `request`
 			request: null,
 			module: null
 		};
@@ -1033,7 +1034,14 @@ class Compilation extends Tapable {
 			slot.request = entry.request;
 		}
 
-		this._preparedEntrypoints.push(slot);
+		// TODO webpack 5: merge modules instead when multiple entry modules are supported
+		const idx = this._preparedEntrypoints.findIndex(slot => slot.name === name);
+		if (idx >= 0) {
+			// Overwrite existing entrypoint
+			this._preparedEntrypoints[idx] = slot;
+		} else {
+			this._preparedEntrypoints.push(slot);
+		}
 		this._addModuleChain(
 			context,
 			entry,
@@ -1049,7 +1057,9 @@ class Compilation extends Tapable {
 					slot.module = module;
 				} else {
 					const idx = this._preparedEntrypoints.indexOf(slot);
-					this._preparedEntrypoints.splice(idx, 1);
+					if (idx >= 0) {
+						this._preparedEntrypoints.splice(idx, 1);
+					}
 				}
 				return callback(null, module);
 			}

test/configCases/entry/override-entry-point/fail.js

@@ -0,0 +1,3 @@
+it("should load correct entry", function() {
+	throw new Error("This entrypoint should not be used");
+});

test/configCases/entry/override-entry-point/ok.js

@@ -0,0 +1,3 @@
+it("should load correct entry", function() {
+	// ok
+});

test/configCases/entry/override-entry-point/test.config.js

@@ -0,0 +1,8 @@
+module.exports = {
+	findBundle: function() {
+		return [
+			"./runtime~main.js",
+			"./main.chunk.js"
+		]
+	}
+};

test/configCases/entry/override-entry-point/webpack.config.js

@@ -0,0 +1,16 @@
+const SingleEntryPlugin = require("../../../../lib/SingleEntryPlugin");
+module.exports = {
+	entry: () => ({}),
+	optimization: {
+		runtimeChunk: true
+	},
+	output: {
+		filename: "[name].js",
+		chunkFilename: "[name].chunk.js"
+	},
+	target: "web",
+	plugins: [
+		new SingleEntryPlugin(__dirname, "./fail", "main"),
+		new SingleEntryPlugin(__dirname, "./ok", "main")
+	]
+};