Remove unused variables with the Babel plugin

- functions were already removed
- variables can be removed when their initializer does not have side effects
- classes can be removed when they have no static blocks

Fixes #21337

external/builder/babel-plugin-pdfjs-preprocessor.mjs

@@ -47,18 +47,31 @@ function handlePreprocessorAction(ctx, actionName, args, path) {
 }
 
 function babelPluginPDFJSPreprocessor(babel, ctx) {
-  function removeUnusedFunctions(path) {
+  function removeUnusedFunctionsAndVariables(path) {
+    const { scope } = path;
     let removed;
     do {
       removed = false;
-      path.scope.crawl();
-      for (const name in path.scope.bindings) {
-        const binding = path.scope.bindings[name];
+      scope.crawl();
+      for (const name in scope.bindings) {
+        const binding = scope.bindings[name];
         if (!binding.referenced) {
           const { path: bindingPath } = binding;
           if (bindingPath.isFunctionDeclaration()) {
             bindingPath.remove();
             removed = true;
+          } else if (
+            bindingPath.isClassDeclaration() &&
+            !bindingPath.node.body.body.some(m => m.type === "StaticBlock")
+          ) {
+            bindingPath.remove();
+            removed = true;
+          } else if (
+            bindingPath.isVariableDeclarator() &&
+            scope.isPure(bindingPath.node.init, false)
+          ) {
+            bindingPath.remove();
+            removed = true;
           }
         }
       }
@@ -113,24 +126,28 @@ function babelPluginPDFJSPreprocessor(babel, ctx) {
       LogicalExpression: {
         exit(path) {
           const { node } = path;
-          if (!t.isBooleanLiteral(node.left)) {
-            return;
+          let leftIsTruthy = false;
+          switch (node.left.type) {
+            case "BooleanLiteral":
+            case "NumericLiteral":
+            case "StringLiteral":
+            case "NullLiteral":
+              leftIsTruthy = Boolean(node.left.value);
+              break;
+            default:
+              return;
           }
 
           switch (node.operator) {
             case "&&":
               // true && expr => expr
               // false && expr => false
-              path.replaceWith(
-                node.left.value === true ? node.right : node.left
-              );
+              path.replaceWith(leftIsTruthy ? node.right : node.left);
               break;
             case "||":
               // true || expr => true
               // false || expr => expr
-              path.replaceWith(
-                node.left.value === true ? node.left : node.right
-              );
+              path.replaceWith(leftIsTruthy ? node.left : node.right);
               break;
           }
         },
@@ -258,7 +275,7 @@ function babelPluginPDFJSPreprocessor(babel, ctx) {
             body.pop();
           }
 
-          removeUnusedFunctions(path);
+          removeUnusedFunctionsAndVariables(path);
         },
       },
       ClassMethod: {
@@ -284,7 +301,7 @@ function babelPluginPDFJSPreprocessor(babel, ctx) {
       Program: {
         exit(path) {
           if (path.node.sourceType === "module") {
-            removeUnusedFunctions(path);
+            removeUnusedFunctionsAndVariables(path);
           }
         },
       },

external/builder/fixtures_babel/constants-expected.js

@@ -13,3 +13,6 @@ var l = true;
 var m = false;
 var n = false;
 var o = true;
+var p = null;
+var q = 1;
+use(a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q);

external/builder/fixtures_babel/constants.js

@@ -13,3 +13,7 @@ var l = 'test' !== 'test2';
 var m = '1' === true;
 var n = !true;
 var o = !false;
+var p = null && 1;
+var q = null || 1;
+
+use(a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q);

external/builder/fixtures_babel/constructors-expected.js

@@ -18,6 +18,8 @@ class E extends A {
 class F {
   constructor() {
     var a = 0;
+    use(a);
   }
 }
 class G {}
+use(B, C, D, E, F, G);

external/builder/fixtures_babel/constructors.js

@@ -24,6 +24,7 @@ class F {
   constructor() {
     if (PDFJSDev.test('TRUE')) {
       var a = 0;
+      use(a);
     }
   }
 }
@@ -32,6 +33,9 @@ class G {
   constructor() {
     if (PDFJSDev.test('FALSE')) {
       var a = 0;
+      use(a);
     }
   }
 }
+
+use(B, C, D, E, F, G);

external/builder/fixtures_babel/deadcode-expected.js

@@ -5,12 +5,12 @@ function f2() {
 }
 f2();
 function f3() {
-  var i = 0;
+  before();
   throw "test";
 }
 f3();
 function f4() {
-  var i = 0;
+  before();
 }
 f4();
 var obj = {
@@ -23,3 +23,4 @@ class C {
 }
 var arrow1 = () => {};
 var arrow2 = () => {};
+use(obj, C, arrow1, arrow2);

external/builder/fixtures_babel/deadcode.js

@@ -1,41 +1,43 @@
 function f1() {
   return;
-  var i = 0;
+  after();
 }
 f1();
 
 function f2() {
   return 1;
-  var i = 0;
+  after();
 }
 f2();
 
 function f3() {
-  var i = 0;
+  before();
   throw "test";
-  var j = 0;
+  after();
 }
 f3();
 
 function f4() {
-  var i = 0;
+  before();
   if (true) {
     return;
   }
   throw "test";
-  var j = 0;
+  after();
 }
 f4();
 
 var obj = {
-  method1() { return; var i = 0; },
+  method1() { return; after(); },
   method2() { return; },
 };
 
 class C {
-  method1() { return; var i = 0; }
+  method1() { return; after(); }
   method2() { return; }
 }
 
-var arrow1 = () => { return; var i = 0; };
+var arrow1 = () => { return; after(); };
 var arrow2 = () => { return; };
+
+use(obj, C, arrow1, arrow2);

external/builder/fixtures_babel/evals-expected.js

@@ -16,3 +16,4 @@ var j = {
 };
 var k = false;
 var l = true;
+use(a, b, c, d, e, f, g, i, j, k, l);

external/builder/fixtures_babel/evals.js

@@ -9,3 +9,5 @@ var i = typeof PDFJSDev === 'undefined' ? PDFJSDev.eval('FALSE') : '0';
 var j = typeof PDFJSDev !== 'undefined' ? PDFJSDev.eval('OBJ.obj') : '0';
 var k = !PDFJSDev.test('TRUE');
 var l = !PDFJSDev.test('FALSE');
+
+use(a, b, c, d, e, f, g, i, j, k, l);

external/builder/fixtures_babel/unused-variable-expected.js

@@ -0,0 +1,7 @@
+let c = 4;
+let e = sideEffect();
+let f = 5;
+use(c);
+{
+  use(f);
+}

external/builder/fixtures_babel/unused-variable.js

@@ -0,0 +1,14 @@
+let a = 1;
+let b = a, c = 4;
+let d = null && sideEffect();
+let e = null || sideEffect();
+let f = 5;
+let g = 6;
+
+use(c);
+
+if (PDFJSDev.test('TRUE')) {
+  use(f);
+} else {
+  use(g);
+}