Faster Source Maps

lib/impl/PluginLifecycle.js

@@ -1,6 +1,6 @@
 let fs = require('fs');
 let path = require('path');
-let { resolvePath, combineSourceMapChain } = require('./utils');
+let { resolvePath, combineSourceMapChainFast } = require('./utils');
 let ErrorHandling = require('./ErrorHandling');
 
 async function _callAsyncHook (self, plugin, hook, args) {
@@ -208,7 +208,7 @@ module.exports = {
                 return { code: result.code, filePath: filePath, map: result.map };
             }, { code, filePath, map: null });
 
-            map = combineSourceMapChain(mapChain, originalCode, filePath);
+            map = await combineSourceMapChainFast(mapChain, originalCode, filePath);
 
             for (let i = 0; i < context.pluginsContext.length; i++) {
                 delete context.pluginsContext[i].__mapChain;

lib/impl/utils.js

@@ -1,5 +1,6 @@
 let path = require('path');
 let SourceMap = require('source-map');
+let SourceMapFast = require('source-map-fast');
 
 function resolvePath (target, current) {
     if (path.isAbsolute(target)) {
@@ -43,9 +44,7 @@ function getNameFromFileName (file) {
     return path.basename(file.replace(/\0/g, '_')).replace(path.extname(file), '')
 }
 
-function combineSourceMapChain (mapChain, original_code, filepath) {
-    // TODO: Proper handling of null maps.
-    let map;
+function prepareSourceMapChain (mapChain, original_code, filepath) {
     mapChain = mapChain.filter(o => o.map && o.map.mappings).reverse();
 
     if (mapChain.length > 1) {
@@ -56,32 +55,57 @@ function combineSourceMapChain (mapChain, original_code, filepath) {
             obj.map.sources = obj.map.sources.length === 1? [filepath + '_' + (index + 1)] : obj.map.sources;
             obj.map.sourcesContent = obj.map.sourcesContent.length === 1? [mapChain[index + 1]? mapChain[index + 1].code : original_code] : obj.map.sourcesContent;
         });
+    }
 
-        let mapGenerator = SourceMap.SourceMapGenerator.fromSourceMap(new SourceMap.SourceMapConsumer(mapChain[0].map));
+    return mapChain;
+}
 
-        for (let i = 1; i < mapChain.length; i++) {
-            mapGenerator.applySourceMap(new SourceMap.SourceMapConsumer(mapChain[i].map))
-        }
+function generateSourceMap (mapChain, mapGenerator, original_code, filepath) {
+    let map;
 
+    if (mapChain.length > 1) {
         map = mapGenerator.toJSON();
-
-        // Remove irrelevant maps.
-        map.sources = map.sources && map.sources.map((s, i) => i !== map.sources.length - 1? '' : s);
-        map.sourcesContent = map.sourcesContent && map.sourcesContent.map((s, i) => i !== map.sourcesContent.length - 1? '' : s);
     } else {
         map = mapChain.length > 0? mapChain[0].map : undefined;
-    }   
+    }
 
     if (map) {
         map.file = filepath;
         map.sources = [filepath];
         map.sourcesContent = [original_code];
     }
-
 
     return map;
 }
 
+function combineSourceMapChain (inputMapChain, original_code, filepath) {
+    let mapGenerator, mapChain = prepareSourceMapChain(inputMapChain, original_code, filepath);
+
+    if (mapChain.length > 1) {
+        mapGenerator = SourceMap.SourceMapGenerator.fromSourceMap(new SourceMap.SourceMapConsumer(mapChain[0].map));
+
+        for (let i = 1; i < mapChain.length; i++) {
+            mapGenerator.applySourceMap(new SourceMap.SourceMapConsumer(mapChain[i].map))
+        }
+    } 
+
+    return generateSourceMap(mapChain, mapGenerator, original_code, filepath);
+}
+
+async function combineSourceMapChainFast (inputMapChain, original_code, filepath) {
+    let mapGenerator, mapChain = prepareSourceMapChain(inputMapChain, original_code, filepath);
+
+    if (mapChain.length > 1) {
+        mapGenerator = SourceMapFast.SourceMapGenerator.fromSourceMap(await new SourceMapFast.SourceMapConsumer(mapChain[0].map));
+
+        for (let i = 1; i < mapChain.length; i++) {
+            mapGenerator.applySourceMap(await new SourceMapFast.SourceMapConsumer(mapChain[i].map))
+        }
+    }
+
+    return generateSourceMap(mapChain, mapGenerator, original_code, filepath);
+}
+
 function applyOutputFileNames (context, bundle) {
     let name_map = {};
 
@@ -136,6 +160,7 @@ module.exports = {
     formatFileName,
     getNameFromFileName,
     combineSourceMapChain,
+    combineSourceMapChainFast,
     applyOutputFileNames,
     emitAssetToBundle
 };

package.json

@@ -26,7 +26,8 @@
     "express-ws": "^4.0.0",
     "magic-string": "^0.25.7",
     "mime-types": "^2.1.24",
-    "source-map": "^0.5.6"
+    "source-map": "^0.5.6",
+    "source-map-fast": "npm:source-map@0.7.3"
   },
   "devDependencies": {
     "chai": "^4.1.2",

test/nollup.js

@@ -2,6 +2,10 @@ let proxyquire = require('proxyquire');
 let path = require('path');
 let fs_impl = require('fs');
 let expect = require('chai').expect;
+let SourceMapFast = require('source-map-fast');
+
+// Source map lib has a check for browser
+window.fetch = undefined;
 
 let fs = {
     '@global': true,
@@ -32,19 +36,19 @@ let fs = {
 
     readFile: function (file, encoding, callback) {
         try {
-            let output = this.readFileSync(file);
-            callback(null, output);
+            let output = this.readFileSync(file, encoding);
+            callback(null, output);     
         } catch (e) {
             callback(e);
         }
     },
 
-    readFileSync: function (file) {
+    readFileSync: function (file, encoding) {
         if (this._stubs[file]) {
             return this._stubs[file]();
         }
 
-        return fs_impl.readFileSync(file, 'utf8');
+        return fs_impl.readFileSync(file, encoding);
     },
 
     reset: function () {