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.

Author: nicolo-ribaudo

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));
+        }
+      },
     },
   };
 }

external/builder/fixtures_babel/blocks-expected.js

@@ -8,3 +8,4 @@ function test() {
   }
   "4";
 }
+test();

external/builder/fixtures_babel/blocks.js

@@ -17,3 +17,4 @@ function test() {
     "4";
   }
 }
+test();

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();

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();

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() {}

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; },

external/builder/fixtures_babel/ifs-expected.js

@@ -16,3 +16,4 @@ if ('1') {
 function f1() {
   "1";
 }
+f1();

external/builder/fixtures_babel/ifs.js

@@ -32,3 +32,4 @@ function f1() {
     "2";
   }
 }
+f1();