adding output.devtoolNamespace option

When loading multiple libraries built with webpack, you can run into
collisions of the sourcemap file paths. For examle, both have
"webpack:///src/index.js".

This change addresses the problem by introducing a new output option
`output.devtoolNamespace` which defaults to `output.library` when
not specified. The defaults moduleFilenameTemplates in all the
sourcemap plugins have been modified to start with:
"webpack://[namespace]/...", where [namespace] will be replaced by
the `output.devtoolNamespace`.

Notice that there are only two slashes following "webpack:" now.
This is to make it behave just as before when not building with a
namespace. When building with a namespace you only get the two
slashes, but from what I've seen the chrome dev tools only care
about the first 2 slashes anyways.

webpack#5767

lib/EvalDevToolModuleTemplatePlugin.js

@@ -10,7 +10,7 @@ const ModuleFilenameHelpers = require("./ModuleFilenameHelpers");
 class EvalDevToolModuleTemplatePlugin {
 	constructor(sourceUrlComment, moduleFilenameTemplate) {
 		this.sourceUrlComment = sourceUrlComment || "\n//# sourceURL=[url]";
-		this.moduleFilenameTemplate = moduleFilenameTemplate || "webpack:///[resourcePath]?[loaders]";
+		this.moduleFilenameTemplate = moduleFilenameTemplate || "webpack://[namespace]/[resourcePath]?[loaders]";
 	}
 
 	apply(moduleTemplate) {

lib/EvalSourceMapDevToolModuleTemplatePlugin.js

@@ -11,7 +11,7 @@ class EvalSourceMapDevToolModuleTemplatePlugin {
 	constructor(compilation, options) {
 		this.compilation = compilation;
 		this.sourceMapComment = options.append || "//# sourceURL=[module]\n//# sourceMappingURL=[url]";
-		this.moduleFilenameTemplate = options.moduleFilenameTemplate || "webpack:///[resource-path]?[hash]";
+		this.moduleFilenameTemplate = options.moduleFilenameTemplate || "webpack://[namespace]/[resource-path]?[hash]";
 		this.options = options;
 	}
 

lib/ModuleFilenameHelpers.js

@@ -26,6 +26,8 @@ ModuleFilenameHelpers.ID = "[id]";
 ModuleFilenameHelpers.REGEXP_ID = /\[id\]/gi;
 ModuleFilenameHelpers.HASH = "[hash]";
 ModuleFilenameHelpers.REGEXP_HASH = /\[hash\]/gi;
+ModuleFilenameHelpers.NAMESPACE = "[namespace]";
+ModuleFilenameHelpers.REGEXP_NAMESPACE = /\[namespace\]/gi;
 
 function getAfter(str, token) {
 	const idx = str.indexOf(token);
@@ -73,6 +75,7 @@ ModuleFilenameHelpers.createFilename = function createFilename(module, moduleFil
 	const allLoaders = getBefore(identifier, "!");
 	const query = getAfter(resource, "?");
 	const resourcePath = resource.substr(0, resource.length - query.length);
+	const namespace = this._moduleNamespace || "";
 	if(typeof moduleFilenameTemplate === "function") {
 		return moduleFilenameTemplate({
 			identifier: identifier,
@@ -83,7 +86,8 @@ ModuleFilenameHelpers.createFilename = function createFilename(module, moduleFil
 			allLoaders: allLoaders,
 			query: query,
 			moduleId: moduleId,
-			hash: hash
+			hash: hash,
+			namespace: namespace
 		});
 	}
 	return moduleFilenameTemplate
@@ -96,7 +100,8 @@ ModuleFilenameHelpers.createFilename = function createFilename(module, moduleFil
 		.replace(ModuleFilenameHelpers.REGEXP_LOADERS, loaders)
 		.replace(ModuleFilenameHelpers.REGEXP_QUERY, query)
 		.replace(ModuleFilenameHelpers.REGEXP_ID, moduleId)
-		.replace(ModuleFilenameHelpers.REGEXP_HASH, hash);
+		.replace(ModuleFilenameHelpers.REGEXP_HASH, hash)
+		.replace(ModuleFilenameHelpers.REGEXP_NAMESPACE, namespace);
 };
 
 ModuleFilenameHelpers.createFooter = function createFooter(module, requestShortener) {
@@ -160,3 +165,7 @@ ModuleFilenameHelpers.matchObject = function matchObject(obj, str) {
 		if(ModuleFilenameHelpers.matchPart(str, obj.exclude)) return false;
 	return true;
 };
+
+ModuleFilenameHelpers.setModuleNamespace = function setModuleNamespace(moduleNamespace) {
+	this._moduleNamespace = moduleNamespace;
+};

lib/SourceMapDevToolPlugin.js

@@ -62,8 +62,8 @@ class SourceMapDevToolPlugin {
 		if(!options) options = {};
 		this.sourceMapFilename = options.filename;
 		this.sourceMappingURLComment = options.append === false ? false : options.append || "\n//# sourceMappingURL=[url]";
-		this.moduleFilenameTemplate = options.moduleFilenameTemplate || "webpack:///[resourcePath]";
-		this.fallbackModuleFilenameTemplate = options.fallbackModuleFilenameTemplate || "webpack:///[resourcePath]?[hash]";
+		this.moduleFilenameTemplate = options.moduleFilenameTemplate || "webpack://[namespace]/[resourcePath]";
+		this.fallbackModuleFilenameTemplate = options.fallbackModuleFilenameTemplate || "webpack://[namespace]/[resourcePath]?[hash]";
 		this.options = options;
 	}
 

lib/WebpackOptionsApply.js

@@ -46,6 +46,7 @@ const FlagDependencyExportsPlugin = require("./FlagDependencyExportsPlugin");
 const SizeLimitsPlugin = require("./performance/SizeLimitsPlugin");
 
 const ResolverFactory = require("enhanced-resolve").ResolverFactory;
+const ModuleFilenameHelpers = require("./ModuleFilenameHelpers");
 
 class WebpackOptionsApply extends OptionsApply {
 	constructor() {
@@ -193,6 +194,12 @@ class WebpackOptionsApply extends OptionsApply {
 			ExternalsPlugin = require("./ExternalsPlugin");
 			compiler.apply(new ExternalsPlugin(options.output.libraryTarget, options.externals));
 		}
+
+		if(!options.output.devtoolNamespace) {
+			options.output.devtoolNamespace = options.output.library;
+		}
+		ModuleFilenameHelpers.setModuleNamespace(options.output.devtoolNamespace);
+
 		let noSources;
 		let legacy;
 		let modern;

schemas/webpackOptionsSchema.json

@@ -326,6 +326,10 @@
             }
           ]
         },
+        "devtoolNamespace": {
+          "description": "Module namespace to use when interpolating filename template string for the sources array in a generated SourceMap. Defaults to `output.library` if not set. It's useful for avoiding runtime collisions in sourcemaps from multiple webpack projects built as libraries.",
+          "type": "string"
+        },
         "filename": {
           "description": "Specifies the name of each output file on disk. You must **not** specify an absolute path here! The `output.path` option determines the location on disk the files are written to, filename is used solely for naming the individual files.",
           "type": "string",