Replace the webpack+acorn transform with a Babel plugin

This commit converts the pdfjsdev-loader transform into a Babel plugin,
to skip a AST->string->AST round-trip.

Before this commit, the webpack build process was:
1. Babel parses the code
2. Babel transforms the AST
3. Babel generates the code
4. Acorn parses the code
5. pdfjsdev-loader transforms the AST
6. @javascript-obfuscator/escodegen generates the code
7. Webpack parses the file
8. Webpack concatenates the files

After this commit, it is reduced to:
1. Babel parses the code
2. Babel transforms the AST
3. babel-plugin-pdfjs-preprocessor transforms the AST
4. Babel generates the code
5. Webpack parses the file
6. Webpack concatenates the files

This change improves the build time by ~25% (tested on MacBook Air M2):
- `gulp lib`: 3.4s to 2.6s
- `gulp dist`: 36s to 29s
- `gulp generic`: 5.5s to 4.0s
- `gulp mozcentral`: 4.7s to 3.2s

The new Babel plugin doesn't support the `saveComments` option of
pdfjsdev-loader, and it just always discards comments. Even though
pdfjsdev-loader supported multiple values for that option, it was
effectively ignored due to `acorn` dropping comments by default.

external/builder/fixtures_esprima/blocks-expected.js

@@ -1,10 +1,10 @@
 function test() {
- "test";
- "1";
- "2";
- "3";
- if ("test") {
-  "5";
- }
- "4";
+  "test";
+  "1";
+  "2";
+  "3";
+  if ("test") {
+    "5";
+  }
+  "4";
 }

external/builder/fixtures_esprima/comments-expected.js

@@ -1,17 +1,17 @@
 function f1() {
- "1";
- "2";
+  "1";
+  "2";
 }
 function f2() {
- "1";
- "2";
+  "1";
+  "2";
 }
 function f3() {
- if ("1") {
-  "1";
- }
- "2";
- if ("3") {
-  "4";
- }
+  if ("1") {
+    "1";
+  }
+  "2";
+  if ("3") {
+    "4";
+  }
 }

external/builder/fixtures_esprima/constants-expected.js

@@ -10,6 +10,6 @@ var i = true;
 var j = false;
 var k = false;
 var l = true;
-var m = '1' === true;
+var m = false;
 var n = false;
 var o = true;

external/builder/fixtures_esprima/deadcode-expected.js

@@ -1,13 +1,21 @@
-function f1() {
-}
+function f1() {}
 function f2() {
- return 1;
+  return 1;
 }
 function f3() {
- var i = 0;
- throw "test";
+  var i = 0;
+  throw "test";
 }
 function f4() {
- var i = 0;
+  var i = 0;
+}
+var obj = {
+  method1() {},
+  method2() {}
+};
+class C {
+  method1() {}
+  method2() {}
 }
-
+var arrow1 = () => {};
+var arrow2 = () => {};

external/builder/fixtures_esprima/deadcode.js

@@ -23,3 +23,15 @@ function f4() {
   var j = 0;
 }
 
+var obj = {
+  method1() { return; var i = 0; },
+  method2() { return; },
+};
+
+class C {
+  method1() { return; var i = 0; }
+  method2() { return; }
+}
+
+var arrow1 = () => { return; var i = 0; };
+var arrow2 = () => { return; };

external/builder/fixtures_esprima/evals-expected.js

@@ -3,11 +3,17 @@ var b = true;
 var c = true;
 var d = false;
 var e = true;
-var f = 'text';
+var f = "text";
 var g = {
- "obj": { "i": 1 },
- "j": 2
+  obj: {
+    i: 1
+  },
+  j: 2
+};
+var h = {
+  test: "test"
 };
-var h = { 'test': 'test' };
 var i = '0';
-var j = { "i": 1 };
+var j = {
+  i: 1
+};

external/builder/fixtures_esprima/evals.json

@@ -1 +1 @@
-{ 'test': 'test' }
+{ "test": "test" }

external/builder/fixtures_esprima/ifs-expected.js

@@ -1,17 +1,17 @@
 if ('test') {
- "1";
+  "1";
 }
 {
- "1";
+  "1";
 }
 {
- "1";
+  "1";
 }
 ;
 {
- "2";
+  "2";
 }
 ;
 if ('1') {
- "1";
+  "1";
 }

external/builder/fixtures_esprima/importalias-expected.js

@@ -1,7 +1,5 @@
-import { Test } from 'import-name';
+import { Test } from "import-name";
 import { Test2 } from './non-alias';
-export {
- Test3
-} from 'import-name';
-var Imp = require('import-name');
+export { Test3 } from "import-name";
+var Imp = require("import-name");
 var Imp2 = require('./non-alias');

external/builder/test-fixtures.mjs

@@ -42,6 +42,12 @@ files.forEach(function (expectationFilename) {
   if (out !== expectation) {
     errors++;
 
+    // Allow regenerating the expected output using
+    //   OVERWRITE=true node ./external/builder/test-fixtures.mjs
+    if (process.env.OVERWRITE) {
+      fs.writeFileSync(expectationFilename, out + "\n");
+    }
+
     console.log("Assertion failed for " + inFilename);
     console.log("--------------------------------------------------");
     console.log("EXPECTED:");

external/builder/test-fixtures_esprima.mjs

@@ -1,7 +1,7 @@
 import { fileURLToPath } from "url";
 import fs from "fs";
 import path from "path";
-import { preprocessPDFJSCode } from "./preprocessor2.mjs";
+import { preprocessPDFJSCode } from "./babel-plugin-pdfjs-preprocessor.mjs";
 
 const __dirname = path.dirname(fileURLToPath(import.meta.url));
 
@@ -48,6 +48,12 @@ files.forEach(function (expectationFilename) {
   if (out !== expectation) {
     errors++;
 
+    // Allow regenerating the expected output using
+    //   OVERWRITE=true node ./external/builder/test-fixtures_esprima.mjs
+    if (process.env.OVERWRITE) {
+      fs.writeFileSync(expectationFilename, out + "\n");
+    }
+
     console.log("Assertion failed for " + inFilename);
     console.log("--------------------------------------------------");
     console.log("EXPECTED:");

gulpfile.mjs

@@ -14,6 +14,10 @@
  */
 /* eslint-env node */
 
+import {
+  babelPluginPDFJSPreprocessor,
+  preprocessPDFJSCode,
+} from "./external/builder/babel-plugin-pdfjs-preprocessor.mjs";
 import { exec, spawn, spawnSync } from "child_process";
 import autoprefixer from "autoprefixer";
 import babel from "@babel/core";
@@ -30,7 +34,6 @@ import postcssDirPseudoClass from "postcss-dir-pseudo-class";
 import postcssDiscardComments from "postcss-discard-comments";
 import postcssNesting from "postcss-nesting";
 import { preprocess } from "./external/builder/builder.mjs";
-import { preprocessPDFJSCode } from "./external/builder/preprocessor2.mjs";
 import rename from "gulp-rename";
 import replace from "gulp-replace";
 import rimraf from "rimraf";
@@ -209,10 +212,11 @@ function createWebpackConfig(
   const isModule = output.library?.type === "module";
   const skipBabel = bundleDefines.SKIP_BABEL;
 
-  // `core-js`, see https://github.com/zloirock/core-js/issues/514,
-  // should be excluded from processing.
-  const babelExcludes = ["node_modules[\\\\\\/]core-js"];
-  const babelExcludeRegExp = new RegExp(`(${babelExcludes.join("|")})`);
+  const babelExcludeRegExp = [
+    // `core-js`, see https://github.com/zloirock/core-js/issues/514,
+    // should be excluded from processing.
+    /node_modules[\\/]core-js/,
+  ];
 
   const babelPresets = skipBabel
     ? undefined
@@ -227,7 +231,15 @@ function createWebpackConfig(
           },
         ],
       ];
-  const babelPlugins = [];
+  const babelPlugins = [
+    [
+      babelPluginPDFJSPreprocessor,
+      {
+        rootPath: __dirname,
+        defines: bundleDefines,
+      },
+    ],
+  ];
 
   const plugins = [];
   if (!disableLicenseHeader) {
@@ -335,14 +347,6 @@ function createWebpackConfig(
             targets: BABEL_TARGETS,
           },
         },
-        {
-          loader: path.join(__dirname, "external/webpack/pdfjsdev-loader.mjs"),
-          options: {
-            rootPath: __dirname,
-            saveComments: false,
-            defines: bundleDefines,
-          },
-        },
       ],
     },
     // Avoid shadowing actual Node.js variables with polyfills, by disabling
@@ -463,7 +467,6 @@ function createSandboxExternal(defines) {
   const licenseHeader = fs.readFileSync("./src/license_header.js").toString();
 
   const ctx = {
-    saveComments: false,
     defines,
   };
   return gulp
@@ -1572,13 +1575,15 @@ function buildLibHelper(bundleDefines, inputStream, outputDir) {
   }
   function preprocessLib(content) {
     const skipBabel = bundleDefines.SKIP_BABEL;
-    content = preprocessPDFJSCode(ctx, content);
     content = babel.transform(content, {
       sourceType: "module",
       presets: skipBabel
         ? undefined
         : [["@babel/preset-env", { loose: false, modules: false }]],
-      plugins: [babelPluginReplaceNonWebpackImport],
+      plugins: [
+        babelPluginReplaceNonWebpackImport,
+        [babelPluginPDFJSPreprocessor, ctx],
+      ],
       targets: BABEL_TARGETS,
     }).code;
     content = content.replaceAll(
@@ -1589,7 +1594,6 @@ function buildLibHelper(bundleDefines, inputStream, outputDir) {
   }
   const ctx = {
     rootPath: __dirname,
-    saveComments: false,
     defines: bundleDefines,
     map: {
       "pdfjs-lib": "../pdf.js",