feat(minifier): remove name from function / class expressions

crates/oxc_minifier/README.md

@@ -23,6 +23,8 @@ The compressor is responsible for rewriting statements and expressions for minim
 - [Properties of the global object defined in the ECMAScript spec](https://tc39.es/ecma262/multipage/global-object.html#sec-global-object) behaves the same as in the spec
   - Examples of properties: `Infinity`, `parseInt`, `Object`, `Promise.resolve`
   - Examples that breaks this assumption: `globalThis.Object = class MyObject {}`
+- The code does not rely on the `name` property of `Function` or `Class`
+  - Examples that breaks this assumption: `function fn() {}; console.log(f.name === 'fn')`
 - [`document.all`](https://tc39.es/ecma262/multipage/additional-ecmascript-features-for-web-browsers.html#sec-IsHTMLDDA-internal-slot) is not used or behaves as a normal object
   - Examples that breaks this assumption: `console.log(typeof document.all === 'undefined')`
 - TDZ violation does not happen

crates/oxc_minifier/src/peephole/minimize_conditional_expression.rs

@@ -426,9 +426,10 @@ impl<'a> PeepholeOptimizations {
         if !matches!(consequent.left, AssignmentTarget::AssignmentTargetIdentifier(_)) {
             return None;
         }
-        if consequent.right.is_anonymous_function_definition() {
-            return None;
-        }
+        // TODO: need this condition when `keep_fnames` is introduced
+        // if consequent.right.is_anonymous_function_definition() {
+        //     return None;
+        // }
         if consequent.operator != AssignmentOperator::Assign
             || consequent.operator != alternate.operator
             || consequent.left.content_ne(&alternate.left)

crates/oxc_minifier/src/peephole/minimize_conditions.rs

@@ -1558,15 +1558,16 @@ mod test {
         test("x ? a = 0 : a = 1", "a = x ? 0 : 1");
         test(
             "x ? a = function foo() { return 'a' } : a = function bar() { return 'b' }",
-            "a = x ? function foo() { return 'a' } : function bar() { return 'b' }",
+            "a = x ? function () { return 'a' } : function () { return 'b' }",
         );
 
         // a.b might have a side effect
         test_same("x ? a.b = 0 : a.b = 1");
         // `a = x ? () => 'a' : () => 'b'` does not set the name property of the function
-        test_same("x ? a = () => 'a' : a = () => 'b'");
-        test_same("x ? a = function () { return 'a' } : a = function () { return 'b' }");
-        test_same("x ? a = class { foo = 'a' } : a = class { foo = 'b' }");
+        // TODO: need to pass these tests when `keep_fnames` are introduced
+        // test_same("x ? a = () => 'a' : a = () => 'b'");
+        // test_same("x ? a = function () { return 'a' } : a = function () { return 'b' }");
+        // test_same("x ? a = class { foo = 'a' } : a = class { foo = 'b' }");
 
         // for non `=` operators, `GetValue(lref)` is called before `Evaluation of AssignmentExpression`
         // so cannot be fold to `a += x ? 0 : 1`

crates/oxc_minifier/src/peephole/substitute_alternate_syntax.rs

@@ -964,6 +964,7 @@ impl<'a> LatePeepholeOptimizations {
         if let Expression::NewExpression(e) = expr {
             Self::try_compress_typed_array_constructor(e, ctx);
         }
+        Self::remove_name_from_expressions(expr, ctx);
 
         if let Some(folded_expr) = match expr {
             Expression::BooleanLiteral(_) => Self::try_compress_boolean(expr, ctx),
@@ -1085,6 +1086,30 @@ impl<'a> LatePeepholeOptimizations {
         }
     }
 
+    /// Remove name from function / class expressions if it is not used.
+    ///
+    /// - `var a = function f() {}` -> `var a = function () {}`
+    /// - `var a = class C {}` -> `var a = class {}`
+    ///
+    /// This compression is not safe if the code relies on `Function::name`.
+    fn remove_name_from_expressions(expr: &mut Expression<'a>, ctx: Ctx<'a, '_>) {
+        match expr {
+            Expression::FunctionExpression(func) => {
+                if func.id.as_ref().is_some_and(|id| !ctx.symbols().symbol_is_used(id.symbol_id()))
+                {
+                    func.id = None;
+                }
+            }
+            Expression::ClassExpression(class) => {
+                if class.id.as_ref().is_some_and(|id| !ctx.symbols().symbol_is_used(id.symbol_id()))
+                {
+                    class.id = None;
+                }
+            }
+            _ => {}
+        }
+    }
+
     /// Whether the name matches any TypedArray name.
     ///
     /// See <https://tc39.es/ecma262/multipage/indexed-collections.html#sec-typedarray-objects> for the list of TypedArrays.
@@ -1259,7 +1284,7 @@ mod test {
         test("x = new Object()", "x = ({})");
         test("x = Object()", "x = ({})");
 
-        test_same("x = (function f(){function Object(){this.x=4}return new Object();})();");
+        test_same("x = (function (){function Object(){this.x=4}return new Object();})();");
 
         test("x = new window.Object", "x = ({})");
         test("x = new window.Object()", "x = ({})");
@@ -1269,8 +1294,8 @@ mod test {
         test("x = window.Object?.()", "x = Object?.()");
 
         test(
-            "x = (function f(){function Object(){this.x=4};return new window.Object;})();",
-            "x = (function f(){function Object(){this.x=4}return {};})();",
+            "x = (function (){function Object(){this.x=4};return new window.Object;})();",
+            "x = (function (){function Object(){this.x=4}return {};})();",
         );
     }
 
@@ -1699,6 +1724,14 @@ mod test {
         );
     }
 
+    #[test]
+    fn test_remove_name_from_expressions() {
+        test("var a = function f() {}", "var a = function () {}");
+        test_same("var a = function f() { return f; }");
+        test("var a = class C {}", "var a = class {}");
+        test_same("var a = class C { foo() { return C } }");
+    }
+
     #[test]
     fn test_compress_is_null_and_to_nullish_coalescing() {
         test("x == null && y", "x ?? y");

tasks/minsize/minsize.snap

@@ -5,23 +5,23 @@ Original   | minified   | minified   | gzip       | gzip       | Fixture
 
 173.90 kB  | 59.54 kB   | 59.82 kB   | 19.18 kB   | 19.33 kB   | moment.js 
 
-287.63 kB  | 89.45 kB   | 90.07 kB   | 30.97 kB   | 31.95 kB   | jquery.js 
+287.63 kB  | 89.44 kB   | 90.07 kB   | 30.96 kB   | 31.95 kB   | jquery.js 
 
-342.15 kB  | 117.61 kB  | 118.14 kB  | 43.45 kB   | 44.37 kB   | vue.js    
+342.15 kB  | 117.46 kB  | 118.14 kB  | 43.33 kB   | 44.37 kB   | vue.js    
 
 544.10 kB  | 71.40 kB   | 72.48 kB   | 25.86 kB   | 26.20 kB   | lodash.js 
 
 555.77 kB  | 271.11 kB  | 270.13 kB  | 88.26 kB   | 90.80 kB   | d3.js     
 
-1.01 MB    | 440.89 kB  | 458.89 kB  | 122.52 kB  | 126.71 kB  | bundle.min.js
+1.01 MB    | 440.48 kB  | 458.89 kB  | 122.41 kB  | 126.71 kB  | bundle.min.js
 
-1.25 MB    | 650.30 kB  | 646.76 kB  | 160.95 kB  | 163.73 kB  | three.js  
+1.25 MB    | 647.42 kB  | 646.76 kB  | 160.30 kB  | 163.73 kB  | three.js  
 
-2.14 MB    | 716.92 kB  | 724.14 kB  | 161.98 kB  | 181.07 kB  | victory.js
+2.14 MB    | 716.51 kB  | 724.14 kB  | 161.81 kB  | 181.07 kB  | victory.js
 
-3.20 MB    | 1.01 MB    | 1.01 MB    | 324.32 kB  | 331.56 kB  | echarts.js
+3.20 MB    | 1.01 MB    | 1.01 MB    | 324.27 kB  | 331.56 kB  | echarts.js
 
-6.69 MB    | 2.28 MB    | 2.31 MB    | 467.77 kB  | 488.28 kB  | antd.js   
+6.69 MB    | 2.28 MB    | 2.31 MB    | 466.21 kB  | 488.28 kB  | antd.js   
 
-10.95 MB   | 3.36 MB    | 3.49 MB    | 861.77 kB  | 915.50 kB  | typescript.js
+10.95 MB   | 3.35 MB    | 3.49 MB    | 861.48 kB  | 915.50 kB  | typescript.js