Switch to GenMapping for sourcemap generation (#1190)

* Switch to GenMapping for sourcemap generation

[`gen-mapping`](https://github.com/jridgewell/gen-mapping) is faster, smaller, and lighter  sourcemap generation library.

This also exposes a new `decodedMap` property on the result object. Decoded maps are free to create (it's a shallow clone of the `GenMapping` instance), and passing them to `@jridgewell/trace-mapping` is copy-free. With Babel  [recently](babel/babel#14497) adding a `decodedMap` field, a dev could pass from the Babel transpilation to Terser without any added memory use for sourcemaps.

And if there's a multi stage build process, a dev could use `@ampproject/remapping` to remap Babel, Terser, and (eg) a bundler's outputs without having to feed input maps into each stage.

* Apply suggestions from code review

Co-authored-by: Fábio Santos <fabiosantosart@gmail.com>

* Fix dependency

* Switch to source-map compatible @jridgewell/source-map

This preserves API compatibility, so that loading source-map in the browser is still supported.

* Update TS types

* Support source-map's async SourceMapConsumer

* Fix sourcesContent check with source-map's SourceMapGenerator

Co-authored-by: Fábio Santos <fabiosantosart@gmail.com>

lib/minify.js

@@ -297,18 +297,15 @@ async function minify(files, options, _fs_module) {
         }
 
         if (options.sourceMap) {
+            if (options.sourceMap.includeSources && files instanceof AST_Toplevel) {
+                throw new Error("original source content unavailable");
+            }
             options.format.source_map = await SourceMap({
                 file: options.sourceMap.filename,
                 orig: options.sourceMap.content,
-                root: options.sourceMap.root
+                root: options.sourceMap.root,
+                files: options.sourceMap.includeSources ? files : null,
             });
-            if (options.sourceMap.includeSources) {
-                if (files instanceof AST_Toplevel) {
-                    throw new Error("original source content unavailable");
-                } else for (var name in files) if (HOP(files, name)) {
-                    options.format.source_map.get().setSourceContent(name, files[name]);
-                }
-            }
         }
         delete options.format.ast;
         delete options.format.code;
@@ -317,11 +314,21 @@ async function minify(files, options, _fs_module) {
         toplevel.print(stream);
         result.code = stream.get();
         if (options.sourceMap) {
-            if(options.sourceMap.asObject) {
-                result.map = options.format.source_map.get().toJSON();
-            } else {
-                result.map = options.format.source_map.toString();
-            }
+            Object.defineProperty(result, "map", {
+                configurable: true,
+                enumerable: true,
+                get() {
+                    const map = options.format.source_map.getEncoded();
+                    return (result.map = options.sourceMap.asObject ? map : JSON.stringify(map));
+                },
+                set(value) {
+                    Object.defineProperty(result, "map", {
+                        value,
+                        writable: true,
+                    });
+                }
+            });
+            result.decoded_map = options.format.source_map.getDecoded();
             if (options.sourceMap.url == "inline") {
                 var sourceMap = typeof result.map === "object" ? JSON.stringify(result.map) : result.map;
                 result.code += "\n//# sourceMappingURL=data:application/json;charset=utf-8;base64," + to_base64(sourceMap);

lib/sourcemap.js

@@ -43,42 +43,47 @@
 
 "use strict";
 
-import MOZ_SourceMap from "source-map";
-import {AnyMap, originalPositionFor} from "@jridgewell/trace-mapping";
-import {defaults} from "./utils/index.js";
+import {SourceMapConsumer, SourceMapGenerator} from "@jridgewell/source-map";
+import {defaults, HOP} from "./utils/index.js";
 
-// a small wrapper around source-map and @jridgewell/trace-mapping
-function SourceMap(options) {
+// a small wrapper around source-map and @jridgewell/source-map
+async function SourceMap(options) {
     options = defaults(options, {
         file : null,
         root : null,
         orig : null,
-
-        orig_line_diff : 0,
-        dest_line_diff : 0,
+        files: {},
     });
 
     var orig_map;
-    var generator = new MOZ_SourceMap.SourceMapGenerator({
+    var generator = new SourceMapGenerator({
         file       : options.file,
         sourceRoot : options.root
     });
 
+    let sourcesContent = {__proto__: null};
+    let files = options.files;
+    for (var name in files) if (HOP(files, name)) {
+        sourcesContent[name] = files[name];
+    }
     if (options.orig) {
-        orig_map = new AnyMap(options.orig);
+        // We support both @jridgewell/source-map (which has a sync
+        // SourceMapConsumer) and source-map (which has an async
+        // SourceMapConsumer).
+        orig_map = await new SourceMapConsumer(options.orig);
         if (orig_map.sourcesContent) {
-            orig_map.resolvedSources.forEach(function(source, i) {
-                var sourceContent = orig_map.sourcesContent[i];
-                if (sourceContent) {
-                    generator.setSourceContent(source, sourceContent);
+            orig_map.sources.forEach(function(source, i) {
+                var content = orig_map.sourcesContent[i];
+                if (content) {
+                    sourcesContent[source] = content;
                 }
             });
         }
     }
 
     function add(source, gen_line, gen_col, orig_line, orig_col, name) {
         if (orig_map) {
-            var info = originalPositionFor(orig_map, {
+            var info = orig_map.originalPositionFor({
                 line: orig_line,
                 column: orig_col
             });
@@ -91,18 +96,42 @@ function SourceMap(options) {
             name = info.name || name;
         }
         generator.addMapping({
-            generated : { line: gen_line + options.dest_line_diff, column: gen_col },
-            original  : { line: orig_line + options.orig_line_diff, column: orig_col },
+            generated : { line: gen_line, column: gen_col },
+            original  : { line: orig_line, column: orig_col },
             source    : source,
             name      : name
         });
+        generator.setSourceContent(source, sourcesContent[source]);
+    }
+
+    function clean(map) {
+        const allNull = map.sourcesContent && map.sourcesContent.every(c => c == null);
+        if (allNull) delete map.sourcesContent;
+        if (map.file === undefined) delete map.file;
+        if (map.sourceRoot === undefined) delete map.sourceRoot;
+        return map;
+    }
+
+    function getDecoded() {
+        if (!generator.toDecodedMap) return null;
+        return clean(generator.toDecodedMap());
+    }
+
+    function getEncoded() {
+        return clean(generator.toJSON());
+    }
+
+    function destroy() {
+        // @jridgewell/source-map's SourceMapConsumer does not need to be
+        // manually freed.
+        if (orig_map && orig_map.destroy) orig_map.destroy();
     }
 
     return {
-        add        : add,
-        get        : function() { return generator; },
-        toString   : function() { return generator.toString(); },
-        destroy    : function() {}
+        add,
+        getDecoded,
+        getEncoded,
+        destroy,
     };
 }
 

package.json

@@ -44,10 +44,9 @@
     "main.js"
   ],
   "dependencies": {
-    "@jridgewell/trace-mapping": "^0.3.5",
+    "@jridgewell/source-map": "^0.3.2",
     "acorn": "^8.5.0",
     "commander": "^2.20.0",
-    "source-map": "~0.8.0-beta.0",
     "source-map-support": "~0.5.20"
   },
   "devDependencies": {
@@ -60,7 +59,8 @@
     "pre-commit": "^1.2.2",
     "rimraf": "^3.0.2",
     "rollup": "2.56.3",
-    "semver": "^7.3.4"
+    "semver": "^7.3.4",
+    "source-map": "~0.8.0-beta.0"
   },
   "scripts": {
     "test": "node test/compress.js && mocha test/mocha",

rollup.config.js

@@ -5,7 +5,7 @@ export default () => {
             file: "dist/bundle.min.js",
             format: "umd",
             globals: {
-                "source-map": "sourceMap",
+                "@jridgewell/source-map": "sourceMap",
             },
             name: "Terser",
             sourcemap: false,

test/mocha/cli-2.js

@@ -21,7 +21,7 @@ describe("bin/terser (2)", function() {
 
             assert.strictEqual(stdout, [
                 '"use strict";var foo=function foo(x){return"foo "+x};console.log(foo("bar"));',
-                "//# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbImluZGV4LmpzIl0sIm5hbWVzIjpbImZvbyIsIngiLCJjb25zb2xlIiwibG9nIl0sIm1hcHBpbmdzIjoiYUFBQSxJQUFJQSxJQUFNLFNBQU5BLElBQU1DLEdBQUEsTUFBSyxPQUFTQSxHQUN4QkMsUUFBUUMsSUFBSUgsSUFBSSJ9",
+                "//# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJuYW1lcyI6WyJmb28iLCJ4IiwiY29uc29sZSIsImxvZyJdLCJzb3VyY2VzIjpbImluZGV4LmpzIl0sIm1hcHBpbmdzIjoiYUFBQSxJQUFJQSxJQUFNLFNBQU5BLElBQU1DLEdBQUEsTUFBSyxPQUFTQSxHQUN4QkMsUUFBUUMsSUFBSUgsSUFBSSJ9",
                 ""
             ].join("\n"));
             done();
@@ -46,7 +46,7 @@ describe("bin/terser (2)", function() {
 
             assert.strictEqual(stdout, [
                 'function foo(){return function(){console.log("PASS")}}foo()();',
-                "//# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbInRlc3QvaW5wdXQvaXNzdWUtMjMxMC9pbnB1dC5qcyJdLCJuYW1lcyI6WyJmb28iLCJjb25zb2xlIiwibG9nIiwiZiJdLCJtYXBwaW5ncyI6IkFBQUEsU0FBU0EsTUFDTCxPQUFPLFdBQ0hDLFFBQVFDLElBQUksU0FLUkYsS0FDUkcifQ==",
+                "//# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJuYW1lcyI6WyJmb28iLCJjb25zb2xlIiwibG9nIiwiZiJdLCJzb3VyY2VzIjpbInRlc3QvaW5wdXQvaXNzdWUtMjMxMC9pbnB1dC5qcyJdLCJtYXBwaW5ncyI6IkFBQUEsU0FBU0EsTUFDTCxPQUFPLFdBQ0hDLFFBQVFDLElBQUksU0FLUkYsS0FDUkcifQ==",
                 ""
             ].join("\n"));
             done();

test/mocha/minify.js

@@ -321,7 +321,7 @@ describe("minify", function() {
             });
             var code = result.code;
             assert.strictEqual(code, "var a=function(n){return n};\n" +
-                "//# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbIjAiXSwibmFtZXMiOlsiYSIsImZvbyJdLCJtYXBwaW5ncyI6IkFBQUEsSUFBSUEsRUFBSSxTQUFTQyxHQUFPLE9BQU9BIn0=");
+                "//# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJuYW1lcyI6WyJhIiwiZm9vIl0sInNvdXJjZXMiOlsiMCJdLCJtYXBwaW5ncyI6IkFBQUEsSUFBSUEsRUFBSSxTQUFTQyxHQUFPLE9BQU9BIn0=");
         });
         it("should not append source map to output js when sourceMapInline is not enabled", async function() {
             var result = await minify("var a = function(foo) { return foo; };");