alexander-akait · Sep 12, 2026 · Sep 11, 2026 · Sep 11, 2026
diff --git a/.changeset/021-cache-optimization-bailouts.md b/.changeset/021-cache-optimization-bailouts.md
@@ -0,0 +1,5 @@
+---
+"webpack": patch
+---
+
+Move diagnostics to `buildInfo.diagnostics`, persisting parse-time bailouts.
diff --git a/lib/Compilation.js b/lib/Compilation.js
@@ -53,6 +53,7 @@ const LazySet = require("./util/LazySet");
 const { getOrInsert } = require("./util/MapHelpers");
 const WeakTupleMap = require("./util/WeakTupleMap");
 const asyncLib = require("./util/async");
+const { replayOptimizationBailouts } = require("./util/buildDiagnostics");
 const { cachedCleverMerge } = require("./util/cleverMerge");
 const {
 	compareErrors,
@@ -1826,6 +1827,7 @@ BREAKING CHANGE: Asset processing hooks in Compilation has been merged into a si
 					if (currentProfile !== undefined) {
 						currentProfile.markBuildingEnd();
 					}
+					replayOptimizationBailouts(this.moduleGraph, module);
 					this.hooks.stillValidModule.call(module);
 					return callback();
 				}
@@ -1846,6 +1848,7 @@ BREAKING CHANGE: Asset processing hooks in Compilation has been merged into a si
 							this.hooks.failedModule.call(module, err);
 							return callback(err);
 						}
+						replayOptimizationBailouts(this.moduleGraph, module);
 						if (currentProfile !== undefined) {
 							currentProfile.markStoringStart();
 						}
@@ -6378,8 +6381,12 @@ This prevents using hashes of each other and should be avoided.`);
 									const buildInfo = /** @type {BuildInfo} */ (module.buildInfo);
 									if (buildInfo.cacheable === false) {
 										cacheable = false;
-										if (buildInfo.notCacheableReasons) {
-											for (const reason of buildInfo.notCacheableReasons) {
+										const moduleDiagnostics = buildInfo.diagnostics;
+										if (
+											moduleDiagnostics !== undefined &&
+											moduleDiagnostics.notCacheableReasons
+										) {
+											for (const reason of moduleDiagnostics.notCacheableReasons) {
 												if (!notCacheableReasons.includes(reason)) {
 													notCacheableReasons.push(reason);
 												}

diff --git a/lib/DefinePlugin.js b/lib/DefinePlugin.js
@@ -20,6 +20,7 @@ const {
 	evaluateToString,
 	toConstantDependency
 } = require("./javascript/JavascriptParserHelpers");
+const { getBuildDiagnostics } = require("./util/buildDiagnostics");
 const createHash = require("./util/createHash");
 const createHooksRegistry = require("./util/createHooksRegistry");
 
@@ -92,8 +93,10 @@ class RuntimeValue {
 		const buildInfo = /** @type {BuildInfo} */ (parser.state.module.buildInfo);
 		if (this.options === true) {
 			buildInfo.cacheable = false;
+			const diagnostics = getBuildDiagnostics(buildInfo);
 			const reasons =
-				buildInfo.notCacheableReasons || (buildInfo.notCacheableReasons = []);
+				diagnostics.notCacheableReasons ||
+				(diagnostics.notCacheableReasons = []);
 			const reason = `DefinePlugin runtime value ${key}`;
 			if (!reasons.includes(reason)) reasons.push(reason);
 		} else {

diff --git a/lib/JavascriptMetaInfoPlugin.js b/lib/JavascriptMetaInfoPlugin.js
@@ -11,6 +11,7 @@ const {
 	JAVASCRIPT_MODULE_TYPE_ESM
 } = require("./ModuleTypeConstants");
 const { getInnerGraphUtils } = require("./optimize/InnerGraph");
+const { recordOptimizationBailout } = require("./util/buildDiagnostics");
 
 /** @import Compiler from "./Compiler" */
 /** @import { BuildInfo } from "./Module" */
@@ -73,9 +74,10 @@ class JavascriptMetaInfoPlugin {
 							const wasEnabled = innerGraph.isEnabled(parser.state);
 							innerGraph.bailout(parser.state);
 							if (wasEnabled) {
-								compilation.moduleGraph
-									.getOptimizationBailout(parser.state.module)
-									.push("Inner graph bailout: eval()");
+								recordOptimizationBailout(
+									buildInfo,
+									"Inner graph bailout: eval()"
+								);
 							}
 						}
 					});

diff --git a/lib/Module.js b/lib/Module.js
@@ -186,24 +186,31 @@ const makeSerializable = require("./util/makeSerializable");
  * @property {Map<string, string>=} exportsBindingSourceByRuntime export definitions `ModuleLibraryPlugin` took over, re-emitted only where the module is wrapped
  */
 
+/**
+ * What a build recorded for stats and the performance hints to report, kept on the build info so a module restored from the cache still has it.
+ * @typedef {object} BuildDiagnostics
+ * @property {string[]=} optimizationBailouts what parser plugins reported as optimization bailouts, replayed into the module graph of every compilation that reuses the module
+ * @property {string=} sideEffectStatement the statement whose side effect keeps the module in the bundle, as `type at location`
+ * @property {number=} ineffectivePureAnnotations how many `#__PURE__` annotations sit where the parser does not read them
+ * @property {number=} topLevelThis how many times the module reads `this` at its top level
+ * @property {boolean=} usesEval true when the module calls `eval` directly
+ * @property {string[]=} notCacheableReasons reasons why the module is not cacheable (e.g. paths of loaders that marked it)
+ */
+
 /**
  * Defines the build info properties common to all module types.
  * Module type specific properties live in the `Known*BuildInfo` typedef of the dedicated module class.
  * @typedef {object} KnownBuildInfo
  * @property {boolean=} cacheable
- * @property {string[]=} notCacheableReasons reasons why the module is not cacheable (e.g. paths of loaders that marked it)
  * @property {boolean=} strict
  * @property {string=} moduleArgument
  * @property {string=} exportsArgument
  * @property {Record<string, Source>=} assets assets added by loaders or plugins
  * @property {Map<string, AssetInfo | undefined>=} assetsInfo
  * @property {Set<string>=} topLevelDeclarations top level declaration names
  * @property {boolean=} isCircular true when the module is part of a circular dependency chain
- * @property {boolean=} usesEval true when the module calls `eval` directly
- * @property {number=} ineffectivePureAnnotations how many `#__PURE__` annotations sit where the parser does not read them
- * @property {number=} topLevelThis how many times the module reads `this` at its top level
- * @property {string=} sideEffectStatement the statement whose side effect keeps the module in the bundle, as `type at location`
  * @property {boolean=} usesTopLevelAwaitForOf module uses top-level `for await…of` or `await using`, which can't be lowered to a generator
+ * @property {BuildDiagnostics=} diagnostics what the build recorded for stats and the performance hints to report
  */
 
 /** @typedef {string | Set<string>} ValueCacheVersion */

diff --git a/lib/NormalModule.js b/lib/NormalModule.js
@@ -33,6 +33,7 @@ const {
 const LazySet = require("./util/LazySet");
 const { isSubset } = require("./util/SetHelpers");
 const { getScheme } = require("./util/URLAbsoluteSpecifier");
+const { getBuildDiagnostics } = require("./util/buildDiagnostics");
 const {
 	concatComparators,
 	keepOriginalOrder,
@@ -1524,7 +1525,8 @@ class NormalModule extends Module {
 				}
 				buildInfo.cacheable = buildInfo.cacheable && result.cacheable;
 				if (result.notCacheableReasons.length > 0) {
-					buildInfo.notCacheableReasons = result.notCacheableReasons;
+					getBuildDiagnostics(buildInfo).notCacheableReasons =
+						result.notCacheableReasons;
 				}
 				processResult(err, result.result);
 			}
@@ -1632,7 +1634,6 @@ class NormalModule extends Module {
 		};
 		this.buildInfo = {
 			cacheable: false,
-			notCacheableReasons: undefined,
 			parsed: true,
 			fileDependencies: undefined,
 			contextDependencies: undefined,
@@ -1651,6 +1652,7 @@ class NormalModule extends Module {
 			inlineExports: undefined,
 			moduleConcatenationBailout: undefined,
 			moduleConcatenationRootBailout: undefined,
+			diagnostics: undefined,
 			needCreateRequire: undefined,
 			usesTopLevelUsingDeclaration: undefined
 		};

diff --git a/lib/WebpackOptionsApply.js b/lib/WebpackOptionsApply.js
@@ -693,12 +693,7 @@ class WebpackOptionsApply extends OptionsApply {
 			const SideEffectsFlagPlugin = require("./optimize/SideEffectsFlagPlugin");
 
 			new SideEffectsFlagPlugin(
-				options.optimization.sideEffects === true,
-				Boolean(
-					options.performance &&
-					options.performance.hints &&
-					options.performance.unusedModules
-				)
+				options.optimization.sideEffects === true
 			).apply(compiler);
 		}
 		if (options.optimization.providedExports) {

diff --git a/lib/dependencies/AMDDefineDependencyParserPlugin.js b/lib/dependencies/AMDDefineDependencyParserPlugin.js
@@ -6,6 +6,7 @@
 "use strict";
 
 const RuntimeGlobals = require("../RuntimeGlobals");
+const { recordOptimizationBailout } = require("../util/buildDiagnostics");
 const AMDDefineDependency = require("./AMDDefineDependency");
 const AMDRequireArrayDependency = require("./AMDRequireArrayDependency");
 const AMDRequireContextDependency = require("./AMDRequireContextDependency");
@@ -35,6 +36,7 @@ const { addLocalModule, getLocalModule } = require("./LocalModulesHelpers");
  * } from "../../declarations/WebpackOptions"
  */
 /** @import Dependency from "../Dependency" */
+/** @import { BuildInfo } from "../Module" */
 /** @import BasicEvaluatedExpression from "../javascript/BasicEvaluatedExpression" */
 /**
  * @import JavascriptParser, {
@@ -353,9 +355,10 @@ class AMDDefineDependencyParserPlugin {
 				return;
 		}
 		DynamicExports.bailout(parser.state);
-		parser.state.compilation.moduleGraph
-			.getOptimizationBailout(parser.state.module)
-			.push("AMD bailout: define() prevents static exports analysis");
+		recordOptimizationBailout(
+			/** @type {BuildInfo} */ (parser.state.module.buildInfo),
+			"AMD bailout: define() prevents static exports analysis"
+		);
 		/** @type {Identifier[] | null} */
 		let fnParams = null;
 		let fnParamsOffset = 0;

diff --git a/lib/dependencies/CommonJsExportsParserPlugin.js b/lib/dependencies/CommonJsExportsParserPlugin.js
@@ -7,6 +7,7 @@
 
 const RuntimeGlobals = require("../RuntimeGlobals");
 const { evaluateToString } = require("../javascript/JavascriptParserHelpers");
+const { recordOptimizationBailout } = require("../util/buildDiagnostics");
 const formatLocation = require("../util/formatLocation");
 const { propertyAccess } = require("../util/property");
 const CommonJsExportRequireDependency = require("./CommonJsExportRequireDependency");
@@ -38,7 +39,7 @@ const FUNCTION_PROPERTY_DROP_HEAD =
  * } from "estree"
  */
 /** @import { ExportInfoName } from "../Dependency" */
-/** @import ModuleGraph from "../ModuleGraph" */
+/** @import { BuildInfo } from "../Module" */
 /** @import BasicEvaluatedExpression from "../javascript/BasicEvaluatedExpression" */
 /**
  * @import JavascriptParser, {
@@ -357,15 +358,6 @@ const getObjectExportKind = (property) => {
 const PLUGIN_NAME = "CommonJsExportsParserPlugin";
 
 class CommonJsExportsParserPlugin {
-	/**
-	 * Creates an instance of CommonJsExportsParserPlugin.
-	 * @param {ModuleGraph} moduleGraph module graph
-	 */
-	constructor(moduleGraph) {
-		/** @type {ModuleGraph} */
-		this.moduleGraph = moduleGraph;
-	}
-
 	/**
 	 * Applies the plugin by registering its hooks on the compiler.
 	 * @param {JavascriptParser} parser the parser
@@ -406,9 +398,10 @@ class CommonJsExportsParserPlugin {
 		 * @param {string} reason reason
 		 */
 		const bailoutHint = (reason) => {
-			this.moduleGraph
-				.getOptimizationBailout(parser.state.module)
-				.push(`CommonJS bailout: ${reason}`);
+			recordOptimizationBailout(
+				/** @type {BuildInfo} */ (parser.state.module.buildInfo),
+				`CommonJS bailout: ${reason}`
+			);
 		};
 		/** @type {unknown} */
 		let keptAllExportsForState;

diff --git a/lib/dependencies/CommonJsPlugin.js b/lib/dependencies/CommonJsPlugin.js
@@ -254,9 +254,7 @@ class CommonJsPlugin {
 					);
 
 					new CommonJsImportsParserPlugin(parserOptions).apply(parser);
-					new CommonJsExportsParserPlugin(compilation.moduleGraph).apply(
-						parser
-					);
+					new CommonJsExportsParserPlugin().apply(parser);
 				};
 
 				normalModuleFactory.hooks.parser

diff --git a/lib/optimize/ConcatenatedModule.js b/lib/optimize/ConcatenatedModule.js
@@ -40,6 +40,7 @@ const {
 } = require("../runtime/MakeDeferredNamespaceObjectRuntime");
 const { equals } = require("../util/ArrayHelpers");
 const LazySet = require("../util/LazySet");
+const { getBuildDiagnostics } = require("../util/buildDiagnostics");
 const {
 	compareModulesByFullName,
 	concatComparators
@@ -1185,15 +1186,17 @@ class ConcatenatedModule extends Module {
 
 		for (const m of this._modules) {
 			// populate cacheable
-			const { cacheable, notCacheableReasons } = /** @type {BuildInfo} */ (
-				m.buildInfo
-			);
+			const { cacheable, diagnostics } = /** @type {BuildInfo} */ (m.buildInfo);
 			if (!cacheable) {
 				this.buildInfo.cacheable = false;
+				const notCacheableReasons =
+					diagnostics === undefined
+						? undefined
+						: diagnostics.notCacheableReasons;
 				if (notCacheableReasons) {
+					const own = getBuildDiagnostics(this.buildInfo);
 					const reasons =
-						this.buildInfo.notCacheableReasons ||
-						(this.buildInfo.notCacheableReasons = []);
+						own.notCacheableReasons || (own.notCacheableReasons = []);
 					for (const reason of notCacheableReasons) {
 						if (!reasons.includes(reason)) reasons.push(reason);
 					}

diff --git a/lib/optimize/SideEffectsFlagPlugin.js b/lib/optimize/SideEffectsFlagPlugin.js
@@ -15,6 +15,10 @@ const HarmonyExportImportedSpecifierDependency = require("../dependencies/Harmon
 const HarmonyImportDependency = require("../dependencies/HarmonyImportDependency");
 const HarmonyImportSpecifierDependency = require("../dependencies/HarmonyImportSpecifierDependency");
 const { ImportPhaseUtils } = require("../dependencies/ImportPhase");
+const {
+	getBuildDiagnostics,
+	recordOptimizationBailout
+} = require("../util/buildDiagnostics");
 const formatLocation = require("../util/formatLocation");
 const { dirname, join, readJson, relative } = require("../util/fs");
 const { getGlobToRegExpSource } = require("../util/globUtils");
@@ -334,13 +338,10 @@ class SideEffectsFlagPlugin {
 	/**
 	 * Creates an instance of SideEffectsFlagPlugin.
 	 * @param {boolean} analyseSource analyse source code for side effects
-	 * @param {boolean=} recordStatement keep the statement that made a module have side effects, for `performance.unusedModules` to report
 	 */
-	constructor(analyseSource = true, recordStatement = false) {
+	constructor(analyseSource = true) {
 		/** @type {boolean} */
 		this._analyseSource = analyseSource;
-		/** @type {boolean} */
-		this._recordStatement = recordStatement;
 	}
 
 	/**
@@ -423,8 +424,6 @@ class SideEffectsFlagPlugin {
 					return module;
 				});
 				if (this._analyseSource) {
-					const recordStatement = this._recordStatement;
-
 					/**
 					 * Processes the provided parser.
 					 * @param {JavascriptParser} parser the parser
@@ -553,20 +552,16 @@ class SideEffectsFlagPlugin {
 								const loc = parser.getLocation(sideEffectsStatement);
 								const at = formatLocation(loc);
 
-								// The bailout lives on the module graph, which the cache does
-								// not restore. Gated: every module here would carry a string.
-								if (recordStatement) {
-									/** @type {BuildInfo} */
-									(parser.state.module.buildInfo).sideEffectStatement =
-										`${type} at ${at}`;
-								}
-
-								moduleGraph
-									.getOptimizationBailout(parser.state.module)
-									.push(
-										() =>
-											`Statement (${type}) with side effects in source code at ${at}`
-									);
+								const buildInfo = /** @type {BuildInfo} */ (
+									parser.state.module.buildInfo
+								);
+								recordOptimizationBailout(
+									buildInfo,
+									`Statement (${type}) with side effects in source code at ${at}`
+								);
+								// `performance.unusedModules` names the statement, so it is kept typed too.
+								getBuildDiagnostics(buildInfo).sideEffectStatement =
+									`${type} at ${at}`;
 							}
 						});
 					};

diff --git a/lib/performance/CacheEffectivenessPlugin.js b/lib/performance/CacheEffectivenessPlugin.js
@@ -65,10 +65,11 @@ class CacheEffectivenessPlugin {
 
 					uncacheable++;
 
+					const notCacheableReasons =
+						buildInfo.diagnostics && buildInfo.diagnostics.notCacheableReasons;
 					const reasons =
-						buildInfo.notCacheableReasons &&
-						buildInfo.notCacheableReasons.length > 0
-							? buildInfo.notCacheableReasons
+						notCacheableReasons && notCacheableReasons.length > 0
+							? notCacheableReasons
 							: [UNSPECIFIED_REASON];
 
 					for (const reason of reasons) {

diff --git a/lib/performance/EvalUsagePlugin.js b/lib/performance/EvalUsagePlugin.js
@@ -11,6 +11,7 @@ const {
 	JAVASCRIPT_MODULE_TYPE_ESM
 } = require("../ModuleTypeConstants");
 const EvalUsageWarning = require("../errors/EvalUsageWarning");
+const { getBuildDiagnostics } = require("../util/buildDiagnostics");
 const { compareStrings } = require("../util/comparators");
 
 /** @import { PerformanceOptions } from "../../declarations/WebpackOptions" */
@@ -59,7 +60,7 @@ class EvalUsagePlugin {
 							parser.state.module.buildInfo
 						);
 
-						buildInfo.usesEval = true;
+						getBuildDiagnostics(buildInfo).usesEval = true;
 					});
 				};
 
@@ -84,7 +85,9 @@ class EvalUsagePlugin {
 						// Every built module carries one, so only the field is in question.
 						const buildInfo = /** @type {BuildInfo} */ (module.buildInfo);
 
-						if (!buildInfo.usesEval) continue;
+						if (!buildInfo.diagnostics || !buildInfo.diagnostics.usesEval) {
+							continue;
+						}
 
 						callers.push(module.readableIdentifier(requestShortener));
 					}