fix: omit empty ignoreList property from source maps (#20319)

xiaoxiaojx · web-flow · commit edfaa0ffd93e · 2026-01-19T16:29:32.000+03:00
diff --git a/.changeset/sourcemap-ignorelist.md b/.changeset/sourcemap-ignorelist.md
@@ -0,0 +1,5 @@
+---
+"webpack": patch
+---
+
+Optimize source map generation: only include `ignoreList` property when it has content, avoiding empty arrays in source maps.
diff --git a/lib/EvalSourceMapDevToolPlugin.js b/lib/EvalSourceMapDevToolPlugin.js
@@ -165,20 +165,23 @@ class EvalSourceMapDevToolPlugin {
 						}
 					);
 					sourceMap.sources = moduleFilenames;
-					sourceMap.ignoreList = options.ignoreList
-						? sourceMap.sources.reduce(
-								/** @type {(acc: number[], sourceName: string, idx: number) => number[]} */ (
-									(acc, sourceName, idx) => {
-										const rule = /** @type {Rules} */ (options.ignoreList);
-										if (ModuleFilenameHelpers.matchPart(sourceName, rule)) {
-											acc.push(idx);
-										}
-										return acc;
+					if (options.ignoreList) {
+						const ignoreList = sourceMap.sources.reduce(
+							/** @type {(acc: number[], sourceName: string, idx: number) => number[]} */ (
+								(acc, sourceName, idx) => {
+									const rule = /** @type {Rules} */ (options.ignoreList);
+									if (ModuleFilenameHelpers.matchPart(sourceName, rule)) {
+										acc.push(idx);
 									}
-								),
-								[]
-							)
-						: [];
+									return acc;
+								}
+							),
+							[]
+						);
+						if (ignoreList.length > 0) {
+							sourceMap.ignoreList = ignoreList;
+						}
+					}
 
 					if (options.noSources) {
 						sourceMap.sourcesContent = undefined;
diff --git a/lib/SourceMapDevToolPlugin.js b/lib/SourceMapDevToolPlugin.js
@@ -435,24 +435,27 @@ class SourceMapDevToolPlugin {
 										moduleToSourceNameMapping.get(m)
 									);
 									sourceMap.sources = /** @type {string[]} */ (moduleFilenames);
-									sourceMap.ignoreList = options.ignoreList
-										? sourceMap.sources.reduce(
-												/** @type {(acc: number[], sourceName: string, idx: number) => number[]} */ (
-													(acc, sourceName, idx) => {
-														const rule = /** @type {Rules} */ (
-															options.ignoreList
-														);
-														if (
-															ModuleFilenameHelpers.matchPart(sourceName, rule)
-														) {
-															acc.push(idx);
-														}
-														return acc;
+									if (options.ignoreList) {
+										const ignoreList = sourceMap.sources.reduce(
+											/** @type {(acc: number[], sourceName: string, idx: number) => number[]} */ (
+												(acc, sourceName, idx) => {
+													const rule = /** @type {Rules} */ (
+														options.ignoreList
+													);
+													if (
+														ModuleFilenameHelpers.matchPart(sourceName, rule)
+													) {
+														acc.push(idx);
 													}
-												),
-												[]
-											)
-										: [];
+													return acc;
+												}
+											),
+											[]
+										);
+										if (ignoreList.length > 0) {
+											sourceMap.ignoreList = ignoreList;
+										}
+									}
 
 									if (options.noSources) {
 										sourceMap.sourcesContent = undefined;
diff --git a/test/configCases/source-map/default-source-map-properties/index.js b/test/configCases/source-map/default-source-map-properties/index.js
@@ -0,0 +1,16 @@
+it("should not include empty ignoreList in source map", () => {
+	const fs = require("fs");
+	const path = require("path");
+	const sourceMapPath = path.join(__dirname, "bundle0.js.map");
+	const sourceMapContent = fs.readFileSync(sourceMapPath, "utf-8");
+
+	expect(sourceMapContent).not.toMatch(/"ignoreList"\s*:\s*\[\s*\]/);
+
+	// Verify default source map properties are present
+	const sourceMap = JSON.parse(sourceMapContent);
+	expect(sourceMap).toHaveProperty("version", 3);
+	expect(sourceMap).toHaveProperty("sources");
+	expect(Array.isArray(sourceMap.sources)).toBe(true);
+	expect(sourceMap.sources.length).toBeGreaterThan(0);
+});
+
diff --git a/test/configCases/source-map/default-source-map-properties/webpack.config.js b/test/configCases/source-map/default-source-map-properties/webpack.config.js
@@ -0,0 +1,8 @@
+"use strict";
+
+/** @type {import("../../../../").Configuration} */
+module.exports = {
+	mode: "development",
+	devtool: "source-map",
+	entry: "./index.js"
+};
diff --git a/test/configCases/source-map/eval-default-source-map-properties/index.js b/test/configCases/source-map/eval-default-source-map-properties/index.js
@@ -0,0 +1,20 @@
+it("should not include empty ignoreList in eval source map", () => {
+	const fs = require("fs");
+	const source = fs.readFileSync(__filename, "utf-8");
+
+	const match = /sourceMappingURL\s*=\s*data:application\/json;charset=utf-8;base64,([A-Za-z0-9+\/=]+)/.exec(
+		source
+	);
+	expect(match).not.toBeNull();
+	const mapString = Buffer.from(match[1], "base64").toString("utf-8");
+
+	expect(mapString).not.toMatch(/"ignoreList"\s*:\s*\[\s*\]/);
+
+	// Verify default source map properties are present
+	const sourceMap = JSON.parse(mapString);
+	expect(sourceMap).toHaveProperty("version", 3);
+	expect(sourceMap).toHaveProperty("sources");
+	expect(Array.isArray(sourceMap.sources)).toBe(true);
+	expect(sourceMap.sources.length).toBeGreaterThan(0);
+});
+
diff --git a/test/configCases/source-map/eval-default-source-map-properties/webpack.config.js b/test/configCases/source-map/eval-default-source-map-properties/webpack.config.js
@@ -0,0 +1,8 @@
+"use strict";
+
+/** @type {import("../../../../").Configuration} */
+module.exports = {
+	mode: "development",
+	devtool: "eval-source-map",
+	entry: "./index.js"
+};

-Original file line number
+Diff line change
@@ @@ -0,0 +1,5 @@ @@
 +---
 +"webpack": patch
 +---
++
 +Optimize source map generation: only include `ignoreList` property when it has content, avoiding empty arrays in source maps.