Use WHATWG's URL to implement all of source-map's URL operations. (#371)

* Use WHATWG's URL to implement all of source-map's URL operations.

* Preserve string-concat sources behavior for absolute-path sources.

* Only use whatwg-url in browser builds.

* Optimize perf to avoid new URL where not strictly needed.

* Cache url -> source index lookups in the consumer.

* Simplify url cache size limiting.

Author: loganfsmyth

lib/source-map-consumer.js

@@ -194,6 +194,8 @@ class BasicSourceMapConsumer extends SourceMapConsumer {
         throw new Error("Unsupported version: " + version);
       }
 
+      that._sourceLookupCache = new Map();
+
       // Pass `true` below to allow duplicate names and sources. While source maps
       // are intended to be compressed and deduplicated, the TypeScript compiler
       // sometimes generates source maps with duplicates in them. See Github issue
@@ -227,18 +229,30 @@ class BasicSourceMapConsumer extends SourceMapConsumer {
    * found.
    */
   _findSourceIndex(aSource) {
+    // In the most common usecases, we'll be constantly looking up the index for the same source
+    // files, so we cache the index lookup to avoid constantly recomputing the full URLs.
+    const cachedIndex = this._sourceLookupCache.get(aSource);
+    if (typeof cachedIndex === "number") {
+      return cachedIndex;
+    }
+
     // Treat the source as map-relative overall by default.
     const sourceAsMapRelative = util.computeSourceURL(null, aSource, this._sourceMapURL);
     if (this._absoluteSources.has(sourceAsMapRelative)) {
-      return this._absoluteSources.indexOf(sourceAsMapRelative);
+      const index = this._absoluteSources.indexOf(sourceAsMapRelative);
+      this._sourceLookupCache.set(aSource, index);
+      return index;
     }
 
     // Fall back to treating the source as sourceRoot-relative.
     const sourceAsSourceRootRelative = util.computeSourceURL(this.sourceRoot, aSource, this._sourceMapURL);
     if (this._absoluteSources.has(sourceAsSourceRootRelative)) {
-      return this._absoluteSources.indexOf(sourceAsSourceRootRelative);
+      const index = this._absoluteSources.indexOf(sourceAsSourceRootRelative);
+      this._sourceLookupCache.set(aSource, index);
+      return index;
     }
 
+    // To avoid this cache growing forever, we do not cache lookup misses.
     return -1;
   }
 

lib/url-browser.js

@@ -0,0 +1,21 @@
+/* -*- Mode: js; js-indent-level: 2; -*- */
+/*
+ * Copyright 2011 Mozilla Foundation and contributors
+ * Licensed under the New BSD license. See LICENSE or:
+ * http://opensource.org/licenses/BSD-3-Clause
+ */
+"use strict";
+
+/**
+ * Browser 'URL' implementations have been found to handle non-standard URL
+ * schemes poorly, and schemes like
+ *
+ *   webpack:///src/folder/file.js
+ *
+ * are very common in source maps. For the time being we use a JS
+ * implementation in these contexts instead. See
+ *
+ * * https://bugzilla.mozilla.org/show_bug.cgi?id=1374505
+ * * https://bugs.chromium.org/p/chromium/issues/detail?id=734880
+ */
+module.exports = require("whatwg-url").URL;

lib/url.js

@@ -0,0 +1,13 @@
+/* -*- Mode: js; js-indent-level: 2; -*- */
+/*
+ * Copyright 2011 Mozilla Foundation and contributors
+ * Licensed under the New BSD license. See LICENSE or:
+ * http://opensource.org/licenses/BSD-3-Clause
+ */
+"use strict";
+
+// Note: This file is overridden in the 'package.json#browser' field to
+// substitute lib/url-browser.js instead.
+
+// Use the URL global for Node 10, and the 'url' module for Node 8.
+module.exports = typeof URL === "function" ? URL : require("url").URL;