From aebe0cb67f0a845ab96d5267efbb29b5fb27d4f5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nicol=C3=B2=20Ribaudo?= <nribaudo@igalia.com>
Date: Tue, 13 May 2025 14:06:44 +0200
Subject: [PATCH] Remove unused OpenJPEG wasm fallback logic

Emscripten generates code that allows the caller to provide the Wasm
module (thorugh Module.instantiateWasm), with a fallback in case
.instantiateWasm is not provided. We always define instantiateWasm, so
we can hard-code the check and let our dead code elimination logic
remove the unused fallback.

This commit also improved the dead code elimination logic so that if
a function declaration becomes unused as a result of removing dead
code, the function itself is removed.
---
 .../babel-plugin-pdfjs-preprocessor.mjs       | 71 +++++++++++--------
 .../builder/fixtures_babel/blocks-expected.js |  1 +
 external/builder/fixtures_babel/blocks.js     |  1 +
 .../fixtures_babel/comments-expected.js       |  3 +
 external/builder/fixtures_babel/comments.js   |  3 +
 .../fixtures_babel/deadcode-expected.js       |  4 ++
 external/builder/fixtures_babel/deadcode.js   |  4 ++
 .../builder/fixtures_babel/ifs-expected.js    |  1 +
 external/builder/fixtures_babel/ifs.js        |  1 +
 .../builder/fixtures_babel/ignore-expected.js |  4 --
 external/builder/fixtures_babel/ignore.js     |  1 -
 .../unused-function-expected.js               |  5 ++
 .../builder/fixtures_babel/unused-function.js | 14 ++++
 gulpfile.mjs                                  | 27 +++++++
 14 files changed, 105 insertions(+), 35 deletions(-)
 delete mode 100644 external/builder/fixtures_babel/ignore-expected.js
 delete mode 100644 external/builder/fixtures_babel/ignore.js
 create mode 100644 external/builder/fixtures_babel/unused-function-expected.js
 create mode 100644 external/builder/fixtures_babel/unused-function.js

diff --git a/external/builder/babel-plugin-pdfjs-preprocessor.mjs b/external/builder/babel-plugin-pdfjs-preprocessor.mjs
index d90613e84..acb227e3e 100644
--- a/external/builder/babel-plugin-pdfjs-preprocessor.mjs
+++ b/external/builder/babel-plugin-pdfjs-preprocessor.mjs
@@ -47,6 +47,25 @@ function handlePreprocessorAction(ctx, actionName, args, path) {
 }
 
 function babelPluginPDFJSPreprocessor(babel, ctx) {
+  function removeUnusedFunctions(path) {
+    let removed;
+    do {
+      removed = false;
+      path.scope.crawl();
+      for (const name in path.scope.bindings) {
+        const binding = path.scope.bindings[name];
+        if (!binding.referenced) {
+          const { path: bindingPath } = binding;
+          if (bindingPath.isFunctionDeclaration()) {
+            bindingPath.remove();
+            removed = true;
+          }
+        }
+      }
+      // If we removed some functions, there might be new unused ones
+    } while (removed);
+  }
+
   return {
     name: "babel-plugin-pdfjs-preprocessor",
     manipulateOptions({ parserOpts }) {
@@ -173,36 +192,6 @@ function babelPluginPDFJSPreprocessor(babel, ctx) {
           path.replaceWith(t.importExpression(source));
         }
       },
-      NewExpression(path) {
-        const { node } = path;
-
-        if (
-          t.isIdentifier(node.callee, { name: "URL" }) &&
-          node.arguments.length === 2
-        ) {
-          const [arg1, arg2] = node.arguments;
-
-          if (
-            arg1.type === "StringLiteral" &&
-            arg1.value.endsWith(".wasm") &&
-            arg2.type === "MemberExpression"
-          ) {
-            // This statement is generated by the Emscripten Compiler (emcc),
-            // however we're manually loading wasm-files and we want to ensure
-            // that bundlers will leave it alone; this *must* include Webpack.
-            arg1.leadingComments = [
-              {
-                type: "CommentBlock",
-                value: "webpackIgnore: true",
-              },
-              {
-                type: "CommentBlock",
-                value: "@vite-ignore",
-              },
-            ];
-          }
-        }
-      },
       "BlockStatement|StaticBlock": {
         // Visit node in post-order so that recursive flattening
         // of blocks works correctly.
@@ -255,6 +244,8 @@ function babelPluginPDFJSPreprocessor(babel, ctx) {
             // Function body ends with return without arg -- removing it.
             body.pop();
           }
+
+          removeUnusedFunctions(path);
         },
       },
       ClassMethod: {
@@ -277,6 +268,26 @@ function babelPluginPDFJSPreprocessor(babel, ctx) {
           }
         },
       },
+      Program: {
+        exit(path) {
+          if (path.node.sourceType === "module") {
+            removeUnusedFunctions(path);
+          }
+        },
+      },
+      MemberExpression(path) {
+        // The Emscripten Compiler (emcc) generates code that allows the caller
+        // to provide the Wasm module (thorugh Module.instantiateWasm), with
+        // a fallback in case .instantiateWasm is not provided.
+        // We always define instantiateWasm, so we can hard-code the check
+        // and let our dead code elimination logic remove the unused fallback.
+        if (
+          path.parentPath.isIfStatement({ test: path.node }) &&
+          path.matchesPattern("Module.instantiateWasm")
+        ) {
+          path.replaceWith(t.booleanLiteral(true));
+        }
+      },
     },
   };
 }
diff --git a/external/builder/fixtures_babel/blocks-expected.js b/external/builder/fixtures_babel/blocks-expected.js
index 22e7b7434..6d2de6e03 100644
--- a/external/builder/fixtures_babel/blocks-expected.js
+++ b/external/builder/fixtures_babel/blocks-expected.js
@@ -8,3 +8,4 @@ function test() {
   }
   "4";
 }
+test();
diff --git a/external/builder/fixtures_babel/blocks.js b/external/builder/fixtures_babel/blocks.js
index a7f3c360d..5267ee81d 100644
--- a/external/builder/fixtures_babel/blocks.js
+++ b/external/builder/fixtures_babel/blocks.js
@@ -17,3 +17,4 @@ function test() {
     "4";
   }
 }
+test();
diff --git a/external/builder/fixtures_babel/comments-expected.js b/external/builder/fixtures_babel/comments-expected.js
index 24488a4b0..00f966a4f 100644
--- a/external/builder/fixtures_babel/comments-expected.js
+++ b/external/builder/fixtures_babel/comments-expected.js
@@ -2,10 +2,12 @@ function f1() {
   "1";
   "2";
 }
+f1();
 function f2() {
   "1";
   "2";
 }
+f2();
 function f3() {
   if ("1") {
     "1";
@@ -15,3 +17,4 @@ function f3() {
     "4";
   }
 }
+f3();
diff --git a/external/builder/fixtures_babel/comments.js b/external/builder/fixtures_babel/comments.js
index 5c7758c6c..4da93e035 100644
--- a/external/builder/fixtures_babel/comments.js
+++ b/external/builder/fixtures_babel/comments.js
@@ -6,6 +6,7 @@ function f1() {
   "2";
   /* tail */
 }
+f1();
 
 function f2() {
   // head
@@ -14,6 +15,7 @@ function f2() {
   "2";
   // tail
 }
+f2();
 
 function f3() {
   if ("1") { // begin block
@@ -24,3 +26,4 @@ function f3() {
     "4";
   }
 }
+f3();
diff --git a/external/builder/fixtures_babel/deadcode-expected.js b/external/builder/fixtures_babel/deadcode-expected.js
index c948acaba..f947370c3 100644
--- a/external/builder/fixtures_babel/deadcode-expected.js
+++ b/external/builder/fixtures_babel/deadcode-expected.js
@@ -1,14 +1,18 @@
 function f1() {}
+f1();
 function f2() {
   return 1;
 }
+f2();
 function f3() {
   var i = 0;
   throw "test";
 }
+f3();
 function f4() {
   var i = 0;
 }
+f4();
 var obj = {
   method1() {},
   method2() {}
diff --git a/external/builder/fixtures_babel/deadcode.js b/external/builder/fixtures_babel/deadcode.js
index c1d8c4fb8..4c2796a3c 100644
--- a/external/builder/fixtures_babel/deadcode.js
+++ b/external/builder/fixtures_babel/deadcode.js
@@ -2,17 +2,20 @@ function f1() {
   return;
   var i = 0;
 }
+f1();
 
 function f2() {
   return 1;
   var i = 0;
 }
+f2();
 
 function f3() {
   var i = 0;
   throw "test";
   var j = 0;
 }
+f3();
 
 function f4() {
   var i = 0;
@@ -22,6 +25,7 @@ function f4() {
   throw "test";
   var j = 0;
 }
+f4();
 
 var obj = {
   method1() { return; var i = 0; },
diff --git a/external/builder/fixtures_babel/ifs-expected.js b/external/builder/fixtures_babel/ifs-expected.js
index db9f4af15..424997844 100644
--- a/external/builder/fixtures_babel/ifs-expected.js
+++ b/external/builder/fixtures_babel/ifs-expected.js
@@ -16,3 +16,4 @@ if ('1') {
 function f1() {
   "1";
 }
+f1();
diff --git a/external/builder/fixtures_babel/ifs.js b/external/builder/fixtures_babel/ifs.js
index 187c7f932..bdf085e69 100644
--- a/external/builder/fixtures_babel/ifs.js
+++ b/external/builder/fixtures_babel/ifs.js
@@ -32,3 +32,4 @@ function f1() {
     "2";
   }
 }
+f1();
diff --git a/external/builder/fixtures_babel/ignore-expected.js b/external/builder/fixtures_babel/ignore-expected.js
deleted file mode 100644
index 0db4463ee..000000000
--- a/external/builder/fixtures_babel/ignore-expected.js
+++ /dev/null
@@ -1,4 +0,0 @@
-const wasmUrl = new URL(
-/*webpackIgnore: true*/
-/*@vite-ignore*/
-"qwerty.wasm", import.meta.url);
diff --git a/external/builder/fixtures_babel/ignore.js b/external/builder/fixtures_babel/ignore.js
deleted file mode 100644
index 74371deac..000000000
--- a/external/builder/fixtures_babel/ignore.js
+++ /dev/null
@@ -1 +0,0 @@
-const wasmUrl = new URL("qwerty.wasm" , import.meta.url);
diff --git a/external/builder/fixtures_babel/unused-function-expected.js b/external/builder/fixtures_babel/unused-function-expected.js
new file mode 100644
index 000000000..bfadac746
--- /dev/null
+++ b/external/builder/fixtures_babel/unused-function-expected.js
@@ -0,0 +1,5 @@
+function usedByUsed() {}
+function used() {
+  usedByUsed();
+}
+used();
diff --git a/external/builder/fixtures_babel/unused-function.js b/external/builder/fixtures_babel/unused-function.js
new file mode 100644
index 000000000..5e89d4210
--- /dev/null
+++ b/external/builder/fixtures_babel/unused-function.js
@@ -0,0 +1,14 @@
+function usedByUsed() {}
+function usedByUnused() {}
+function usedByRemovedCode() {}
+
+function used() {
+  usedByUsed();
+  return;
+  usedByRemovedCode();
+}
+function unused() {
+  usedByUnused();
+}
+
+used();
diff --git a/gulpfile.mjs b/gulpfile.mjs
index 0c53f9031..3db31c758 100644
--- a/gulpfile.mjs
+++ b/gulpfile.mjs
@@ -339,6 +339,33 @@ function createWebpackConfig(
       new webpack2.BannerPlugin({ banner: licenseHeaderLibre, raw: true })
     );
   }
+  plugins.push({
+    /** @param {import('webpack').Compiler} compiler */
+    apply(compiler) {
+      const errors = [];
+
+      compiler.hooks.afterCompile.tap("VerifyImportMeta", compilation => {
+        for (const asset of compilation.getAssets()) {
+          if (asset.name.endsWith(".mjs")) {
+            const source = asset.source.source();
+            if (
+              typeof source === "string" &&
+              /new URL\([^,)]*,\s*import\.meta\.url/.test(source)
+            ) {
+              errors.push(
+                `Output module ${asset.name} uses new URL(..., import.meta.url)`
+              );
+            }
+          }
+        }
+      });
+      compiler.hooks.afterEmit.tap("VerifyImportMeta", compilation => {
+        // Emit the errors after emitting the files, so that it's possible to
+        // look at the contents of the invalid bundle.
+        compilation.errors.push(...errors);
+      });
+    },
+  });
 
   const alias = createWebpackAlias(bundleDefines);
   const experiments = isModule ? { outputModule: true } : undefined;