offer getResolve to externals

declarations/WebpackOptions.d.ts

@@ -150,14 +150,13 @@ export type ExternalItem =
 	| RegExp
 	| string
 	| (ExternalItemObjectKnown & ExternalItemObjectUnknown)
-	| ((
-			data: {
-				context: string;
-				request: string;
-				contextInfo: import("../lib/ModuleFactory").ModuleFactoryCreateDataContextInfo;
-			},
-			callback: (err?: Error, result?: string) => void
-	  ) => void);
+	| (
+			| ((
+					data: ExternalItemFunctionData,
+					callback: (err?: Error, result?: ExternalItemValue) => void
+			  ) => void)
+			| ((data: ExternalItemFunctionData) => Promise<ExternalItemValue>)
+	  );
 /**
  * Specifies the default type of externals ('amd*', 'umd*', 'system' and 'jsonp' depend on output.libraryTarget set to the same value).
  */
@@ -642,6 +641,16 @@ export type EntryDynamicNormalized = () => Promise<EntryStaticNormalized>;
  * The entry point(s) of the compilation.
  */
 export type EntryNormalized = EntryDynamicNormalized | EntryStaticNormalized;
+/**
+ * The dependency used for the external.
+ */
+export type ExternalItemValue =
+	| string[]
+	| boolean
+	| string
+	| {
+			[k: string]: any;
+	  };
 /**
  * Ignore specific warnings.
  */
@@ -2501,6 +2510,35 @@ export interface EntryStaticNormalized {
 	 */
 	[k: string]: EntryDescriptionNormalized;
 }
+/**
+ * Data object passed as argument when a function is set for 'externals'.
+ */
+export interface ExternalItemFunctionData {
+	/**
+	 * The directory in which the request is placed.
+	 */
+	context?: string;
+	/**
+	 * Contextual information.
+	 */
+	contextInfo?: import("../lib/ModuleFactory").ModuleFactoryCreateDataContextInfo;
+	/**
+	 * Get a resolve function with the current resolver options.
+	 */
+	getResolve?: (
+		options?: ResolveOptions
+	) =>
+		| ((
+				context: string,
+				request: string,
+				callback: (err?: Error, result?: string) => void
+		  ) => void)
+		| ((context: string, request: string) => Promise<string>);
+	/**
+	 * The request as written by the user in the require/import expression/statement.
+	 */
+	request?: string;
+}
 /**
  * Parser options for javascript modules.
  */
@@ -2890,16 +2928,7 @@ export interface ExternalItemObjectKnown {
  * If an dependency matches exactly a property of the object, the property value is used as dependency.
  */
 export interface ExternalItemObjectUnknown {
-	/**
-	 * The dependency used for the external.
-	 */
-	[k: string]:
-		| string[]
-		| boolean
-		| string
-		| {
-				[k: string]: any;
-		  };
+	[k: string]: ExternalItemValue;
 }
 /**
  * Specify options for each generator.

lib/ExternalModuleFactoryPlugin.js

@@ -7,12 +7,13 @@
 
 const util = require("util");
 const ExternalModule = require("./ExternalModule");
-const { resolveByProperty } = require("./util/cleverMerge");
+const { resolveByProperty, cachedSetProperty } = require("./util/cleverMerge");
 
 /** @typedef {import("../declarations/WebpackOptions").Externals} Externals */
 /** @typedef {import("./NormalModuleFactory")} NormalModuleFactory */
 
 const UNSPECIFIED_EXTERNAL_TYPE_REGEXP = /^[a-z0-9]+ /;
+const EMPTY_RESOLVE_OPTIONS = {};
 
 // TODO webpack 6 remove this
 const callDeprecatedExternals = util.deprecate(
@@ -171,14 +172,56 @@ class ExternalModuleFactoryPlugin {
 								cb
 							);
 						} else {
-							externals(
+							const promise = externals(
 								{
 									context,
 									request: dependency.request,
-									contextInfo
+									contextInfo,
+									getResolve: options => (context, request, callback) => {
+										const dependencyType = dependency.category || "";
+										const resolveContext = {
+											fileDependencies: data.fileDependencies,
+											missingDependencies: data.missingDependencies,
+											contextDependencies: data.contextDependencies
+										};
+										let resolver = normalModuleFactory.getResolver(
+											"normal",
+											dependencyType
+												? cachedSetProperty(
+														data.resolveOptions || EMPTY_RESOLVE_OPTIONS,
+														"dependencyType",
+														dependencyType
+												  )
+												: data.resolveOptions
+										);
+										if (options) resolver = resolver.withOptions(options);
+										if (callback) {
+											resolver.resolve(
+												{},
+												context,
+												request,
+												resolveContext,
+												callback
+											);
+										} else {
+											return new Promise((resolve, reject) => {
+												resolver.resolve(
+													{},
+													context,
+													request,
+													resolveContext,
+													(err, result) => {
+														if (err) reject(err);
+														else resolve(result);
+													}
+												);
+											});
+										}
+									}
 								},
 								cb
 							);
+							if (promise && promise.then) promise.then(r => cb(null, r), cb);
 						}
 						return;
 					} else if (typeof externals === "object") {

schemas/WebpackOptions.json

@@ -611,28 +611,7 @@
           "description": "If an dependency matches exactly a property of the object, the property value is used as dependency.",
           "type": "object",
           "additionalProperties": {
-            "description": "The dependency used for the external.",
-            "anyOf": [
-              {
-                "type": "array",
-                "items": {
-                  "description": "A part of the target of the external.",
-                  "type": "string",
-                  "minLength": 1
-                }
-              },
-              {
-                "description": "`true`: The dependency name is used as target of the external.",
-                "type": "boolean"
-              },
-              {
-                "description": "The target of the external.",
-                "type": "string"
-              },
-              {
-                "type": "object"
-              }
-            ]
+            "$ref": "#/definitions/ExternalItemValue"
           },
           "properties": {
             "byLayer": {
@@ -655,7 +634,56 @@
         {
           "description": "The function is called on each dependency (`function(context, request, callback(err, result))`).",
           "instanceof": "Function",
-          "tsType": "((data: { context: string, request: string, contextInfo: import('../lib/ModuleFactory').ModuleFactoryCreateDataContextInfo }, callback: (err?: Error, result?: string) => void) => void)"
+          "tsType": "(((data: ExternalItemFunctionData, callback: (err?: Error, result?: ExternalItemValue) => void) => void) | ((data: ExternalItemFunctionData) => Promise<ExternalItemValue>))"
+        }
+      ]
+    },
+    "ExternalItemFunctionData": {
+      "description": "Data object passed as argument when a function is set for 'externals'.",
+      "type": "object",
+      "additionalProperties": false,
+      "properties": {
+        "context": {
+          "description": "The directory in which the request is placed.",
+          "type": "string"
+        },
+        "contextInfo": {
+          "description": "Contextual information.",
+          "type": "object",
+          "tsType": "import('../lib/ModuleFactory').ModuleFactoryCreateDataContextInfo"
+        },
+        "getResolve": {
+          "description": "Get a resolve function with the current resolver options.",
+          "instanceof": "Function",
+          "tsType": "((options?: ResolveOptions) => ((context: string, request: string, callback: (err?: Error, result?: string) => void) => void) | ((context: string, request: string) => Promise<string>))"
+        },
+        "request": {
+          "description": "The request as written by the user in the require/import expression/statement.",
+          "type": "string"
+        }
+      }
+    },
+    "ExternalItemValue": {
+      "description": "The dependency used for the external.",
+      "anyOf": [
+        {
+          "type": "array",
+          "items": {
+            "description": "A part of the target of the external.",
+            "type": "string",
+            "minLength": 1
+          }
+        },
+        {
+          "description": "`true`: The dependency name is used as target of the external.",
+          "type": "boolean"
+        },
+        {
+          "description": "The target of the external.",
+          "type": "string"
+        },
+        {
+          "type": "object"
         }
       ]
     },

test/configCases/externals/resolve/index.js

@@ -0,0 +1,5 @@
+it("should allow functions as externals with promise and resolver", function () {
+	const result = require("external");
+	expect(result).toMatch(/^[a-z]:\\|\//i);
+	expect(result).toMatch(/resolve.node_modules.external\.js$/);
+});

test/configCases/externals/resolve/webpack.config.js

@@ -0,0 +1,14 @@
+/** @type {import("../../../../").Configuration} */
+module.exports = {
+	optimization: {
+		concatenateModules: true
+	},
+	externals: [
+		async ({ context, request, getResolve }) => {
+			if (request !== "external") return false;
+			const resolve = getResolve();
+			const resolved = await resolve(context, request);
+			return `var ${JSON.stringify(resolved)}`;
+		}
+	]
+};

types.d.ts

@@ -1797,13 +1797,13 @@ declare interface Configuration {
 		| ExternalItem[]
 		| (ExternalItemObjectKnown & ExternalItemObjectUnknown)
 		| ((
-				data: {
-					context: string;
-					request: string;
-					contextInfo: ModuleFactoryCreateDataContextInfo;
-				},
-				callback: (err?: Error, result?: string) => void
-		  ) => void);
+				data: ExternalItemFunctionData,
+				callback: (
+					err?: Error,
+					result?: string | boolean | string[] | { [index: string]: any }
+				) => void
+		  ) => void)
+		| ((data: ExternalItemFunctionData) => Promise<ExternalItemValue>);
 
 	/**
 	 * Enable presets of externals for specific targets.
@@ -3247,13 +3247,46 @@ type ExternalItem =
 	| RegExp
 	| (ExternalItemObjectKnown & ExternalItemObjectUnknown)
 	| ((
-			data: {
-				context: string;
-				request: string;
-				contextInfo: ModuleFactoryCreateDataContextInfo;
-			},
-			callback: (err?: Error, result?: string) => void
-	  ) => void);
+			data: ExternalItemFunctionData,
+			callback: (
+				err?: Error,
+				result?: string | boolean | string[] | { [index: string]: any }
+			) => void
+	  ) => void)
+	| ((data: ExternalItemFunctionData) => Promise<ExternalItemValue>);
+
+/**
+ * Data object passed as argument when a function is set for 'externals'.
+ */
+declare interface ExternalItemFunctionData {
+	/**
+	 * The directory in which the request is placed.
+	 */
+	context?: string;
+
+	/**
+	 * Contextual information.
+	 */
+	contextInfo?: ModuleFactoryCreateDataContextInfo;
+
+	/**
+	 * Get a resolve function with the current resolver options.
+	 */
+	getResolve?: (
+		options?: ResolveOptionsWebpackOptions
+	) =>
+		| ((
+				context: string,
+				request: string,
+				callback: (err?: Error, result?: string) => void
+		  ) => void)
+		| ((context: string, request: string) => Promise<string>);
+
+	/**
+	 * The request as written by the user in the require/import expression/statement.
+	 */
+	request?: string;
+}
 
 /**
  * If an dependency matches exactly a property of the object, the property value is used as dependency.
@@ -3271,8 +3304,9 @@ declare interface ExternalItemObjectKnown {
  * If an dependency matches exactly a property of the object, the property value is used as dependency.
  */
 declare interface ExternalItemObjectUnknown {
-	[index: string]: string | boolean | string[] | { [index: string]: any };
+	[index: string]: ExternalItemValue;
 }
+type ExternalItemValue = string | boolean | string[] | { [index: string]: any };
 declare class ExternalModule extends Module {
 	constructor(request?: any, type?: any, userRequest?: any);
 	request: string | string[] | Record<string, string | string[]>;
@@ -3294,13 +3328,13 @@ type Externals =
 	| ExternalItem[]
 	| (ExternalItemObjectKnown & ExternalItemObjectUnknown)
 	| ((
-			data: {
-				context: string;
-				request: string;
-				contextInfo: ModuleFactoryCreateDataContextInfo;
-			},
-			callback: (err?: Error, result?: string) => void
-	  ) => void);
+			data: ExternalItemFunctionData,
+			callback: (
+				err?: Error,
+				result?: string | boolean | string[] | { [index: string]: any }
+			) => void
+	  ) => void)
+	| ((data: ExternalItemFunctionData) => Promise<ExternalItemValue>);
 declare class ExternalsPlugin {
 	constructor(type: undefined | string, externals: Externals);
 	type?: string;