add logging API

declarations/WebpackOptions.d.ts

@@ -1343,6 +1343,18 @@ export interface StatsOptions {
 	 * add the hash of the compilation
 	 */
 	hash?: boolean;
+	/**
+	 * Include debug logging of specified modules (plugins/loaders). Filters can be Strings, RegExps or Functions
+	 */
+	includeDebugLogging?: FilterTypes;
+	/**
+	 * add logging output
+	 */
+	logging?: boolean | ("error" | "warn" | "info" | "log" | "verbose");
+	/**
+	 * add stack traces to logging output
+	 */
+	loggingTrace?: boolean;
 	/**
 	 * Set the maximum number of modules to be shown
 	 */

lib/Compilation.js

@@ -36,6 +36,8 @@ const SortableSet = require("./util/SortableSet");
 const GraphHelpers = require("./GraphHelpers");
 const ModuleDependency = require("./dependencies/ModuleDependency");
 const compareLocations = require("./compareLocations");
+const { Logger, LogType } = require("./logging/Logger");
+const ErrorHelpers = require("./ErrorHelpers");
 
 /** @typedef {import("./Module")} Module */
 /** @typedef {import("./Compiler")} Compiler */
@@ -95,6 +97,13 @@ const compareLocations = require("./compareLocations");
  * @property {DependenciesBlockVariable[]} variables
  */
 
+/**
+ * @typedef {Object} LogEntry
+ * @property {string} type
+ * @property {any[]} args
+ * @property {string[]=} trace
+ */
+
 /**
  * @param {Chunk} a first chunk to sort by id
  * @param {Chunk} b second chunk to sort by id
@@ -384,6 +393,9 @@ class Compilation extends Tapable {
 				"compilerIndex"
 			]),
 
+			/** @type {SyncBailHook<string, LogEntry>} */
+			log: new SyncBailHook(["origin", "logEntry"]),
+
 			// TODO the following hooks are weirdly located here
 			// TODO move them for webpack 5
 			/** @type {SyncHook<object, Module>} */
@@ -469,6 +481,8 @@ class Compilation extends Tapable {
 		this.warnings = [];
 		/** @type {Compilation[]} */
 		this.children = [];
+		/** @type {Map<string, LogEntry[]>} */
+		this.logging = new Map();
 		/** @type {Map<DepConstructor, ModuleFactory>} */
 		this.dependencyFactories = new Map();
 		/** @type {Map<DepConstructor, DependencyTemplate>} */
@@ -499,6 +513,67 @@ class Compilation extends Tapable {
 		return new Stats(this);
 	}
 
+	/**
+	 * @param {string | (function(): string)} name name of the logger, or function called once to get the logger name
+	 * @returns {Logger} a logger with that name
+	 */
+	getLogger(name) {
+		if (!name) {
+			throw new TypeError("Compilation.getLogger(name) called without a name");
+		}
+		let logEntries;
+		return new Logger((type, args) => {
+			if (typeof name === "function") {
+				name = name();
+				if (!name) {
+					throw new TypeError(
+						"Compilation.getLogger(name) called with a function not returning a name"
+					);
+				}
+			}
+			let trace;
+			switch (type) {
+				case LogType.profile:
+					// eslint-disable-next-line node/no-unsupported-features/node-builtins
+					if (typeof console.profile === "function") {
+						// eslint-disable-next-line node/no-unsupported-features/node-builtins
+						console.profile(`[${name}] ${args[0]}`);
+					}
+					return;
+				case LogType.profileEnd:
+					// eslint-disable-next-line node/no-unsupported-features/node-builtins
+					if (typeof console.profileEnd === "function") {
+						// eslint-disable-next-line node/no-unsupported-features/node-builtins
+						console.profileEnd(`[${name}] ${args[0]}`);
+					}
+					return;
+				case LogType.warn:
+				case LogType.error:
+				case LogType.trace:
+					trace = ErrorHelpers.cutOffLoaderExecution(new Error("Trace").stack)
+						.split("\n")
+						.slice(3);
+					break;
+			}
+			const logEntry = {
+				time: Date.now(),
+				type,
+				args,
+				trace
+			};
+			if (this.hooks.log.call(name, logEntry) === undefined) {
+				if (logEntries === undefined) {
+					logEntries = this.logging.get(name);
+					if (logEntries === undefined) {
+						logEntries = [];
+						this.logging.set(name, logEntries);
+					}
+				}
+				logEntries.push(logEntry);
+			}
+		});
+	}
+
 	/**
 	 * @typedef {Object} AddModuleResult
 	 * @property {Module} module the added or existing module

lib/Compiler.js

@@ -27,6 +27,8 @@ const ResolverFactory = require("./ResolverFactory");
 const RequestShortener = require("./RequestShortener");
 const { makePathsRelative } = require("./util/identifier");
 const ConcurrentCompilationError = require("./ConcurrentCompilationError");
+const { Logger, LogType } = require("./logging/Logger");
+const logToConsole = require("./logging/logToConsole");
 
 /** @typedef {import("../declarations/WebpackOptions").Entry} Entry */
 /** @typedef {import("../declarations/WebpackOptions").WebpackOptions} WebpackOptions */
@@ -84,6 +86,9 @@ class Compiler extends Tapable {
 			/** @type {SyncHook} */
 			watchClose: new SyncHook([]),
 
+			/** @type {SyncBailHook<string, string, any[]>} */
+			log: new SyncBailHook(["origin", "type", "args"]),
+
 			// TODO the following hooks are weirdly located here
 			// TODO move them for webpack 5
 			/** @type {SyncHook} */
@@ -196,6 +201,33 @@ class Compiler extends Tapable {
 		this._assetEmittingWrittenFiles = new Map();
 	}
 
+	/**
+	 * @param {string | (function(): string)} name name of the logger, or function called once to get the logger name
+	 * @returns {Logger} a logger with that name
+	 */
+	getInfrastructureLogger(name) {
+		if (!name) {
+			throw new TypeError(
+				"Compiler.getInfrastructureLogger(name) called without a name"
+			);
+		}
+		return new Logger((type, args) => {
+			if (typeof name === "function") {
+				name = name();
+				if (!name) {
+					throw new TypeError(
+						"Compiler.getInfrastructureLogger(name) called with a function not returning a name"
+					);
+				}
+			}
+			if (this.hooks.log.call(name, type, args) === undefined) {
+				// ignore debug logging by default
+				if (type === LogType.debug) return;
+				logToConsole(name, type, args);
+			}
+		});
+	}
+
 	watch(watchOptions, handler) {
 		if (this.running) return handler(new ConcurrentCompilationError());
 

lib/NormalModule.js

@@ -147,30 +147,41 @@ class NormalModule extends Module {
 
 	createLoaderContext(resolver, options, compilation, fs) {
 		const requestShortener = compilation.runtimeTemplate.requestShortener;
+		const getCurrentLoaderName = () => {
+			const currentLoader = this.getCurrentLoader(loaderContext);
+			if (!currentLoader) return "(not in loader scope)";
+			return requestShortener.shorten(currentLoader.loader);
+		};
 		const loaderContext = {
 			version: 2,
 			emitWarning: warning => {
 				if (!(warning instanceof Error)) {
 					warning = new NonErrorEmittedError(warning);
 				}
-				const currentLoader = this.getCurrentLoader(loaderContext);
 				this.warnings.push(
 					new ModuleWarning(this, warning, {
-						from: requestShortener.shorten(currentLoader.loader)
+						from: getCurrentLoaderName()
 					})
 				);
 			},
 			emitError: error => {
 				if (!(error instanceof Error)) {
 					error = new NonErrorEmittedError(error);
 				}
-				const currentLoader = this.getCurrentLoader(loaderContext);
 				this.errors.push(
 					new ModuleError(this, error, {
-						from: requestShortener.shorten(currentLoader.loader)
+						from: getCurrentLoaderName()
 					})
 				);
 			},
+			getLogger: name => {
+				const currentLoader = this.getCurrentLoader(loaderContext);
+				return compilation.getLogger(() =>
+					[currentLoader && currentLoader.loader, name, this.identifier()]
+						.filter(Boolean)
+						.join(" ")
+				);
+			},
 			// TODO remove in webpack 5
 			exec: (code, filename) => {
 				// @ts-ignore Argument of type 'this' is not assignable to parameter of type 'Module'.