fix(es/minifier): Remove unused arrow functions in dead code elimination (#11319)

## Description

This PR fixes issue #11303 where the minifier was preserving unused
arrow functions.

## Root Cause

The `ignore_return_value` method in the optimizer handled function
expressions (Expr::Fn) by returning None (indicating no side effects),
but did not handle arrow functions (Expr::Arrow) the same way. Arrow
functions would fall through to the default case and be preserved even
when unused.

## Changes

- Added handling for Expr::Arrow in ignore_return_value method
- Arrow functions are now treated as side-effect-free expressions
- Added test case for issue #11303
- Updated tinymce test expectation to reflect more aggressive
optimization

## Test Results

All 2790 tests pass.

Closes #11303

🤖 Generated with [Claude Code](https://claude.ai/code)

---------

Co-authored-by: claude[bot] <41898282+claude[bot]@users.noreply.github.com>
Co-authored-by: Donny/강동윤 <kdy1@users.noreply.github.com>

Author: kdy1

.changeset/stupid-worms-boil.md

@@ -1,5 +1,5 @@
 //// [parserArrowFunctionExpression10.ts]
 //// [fileJs.js]
-a || ((e)=>f);
+a;
 //// [fileTs.ts]
-a || ((e)=>f);
+a;

crates/swc/tests/tsc-references/parserArrowFunctionExpression10.2.minified.js

@@ -1,5 +1,5 @@
 //// [parserArrowFunctionExpression12.ts]
 //// [fileJs.js]
-a || ((d)=>e);
+a;
 //// [fileTs.ts]
-a || ((d)=>e);
+a;

crates/swc/tests/tsc-references/parserArrowFunctionExpression12.2.minified.js

@@ -1,5 +1,5 @@
 //// [parserArrowFunctionExpression13.ts]
 //// [fileJs.js]
-a || (()=>null);
+a;
 //// [fileTs.ts]
-a || (()=>null);
+a;

crates/swc/tests/tsc-references/parserArrowFunctionExpression13.2.minified.js

@@ -1,9 +1,5 @@
 //// [parserArrowFunctionExpression8.ts]
 //// [fileJs.js]
-x || ((z)=>({
-        z
-    }));
+x;
 //// [fileTs.ts]
-x || ((z)=>({
-        z
-    }));
+x;

crates/swc/tests/tsc-references/parserArrowFunctionExpression8.2.minified.js

@@ -658,6 +658,16 @@ impl Optimizer<'_> {
                 return None;
             }
 
+            // Arrow function expression cannot have a side effect.
+            Expr::Arrow(_) => {
+                report_change!(
+                    "ignore_return_value: Dropping unused arrow expr as it does not have any side \
+                     effect"
+                );
+                self.changed = true;
+                return None;
+            }
+
             Expr::Class(cls) => {
                 // Do not remove class if it's self-referencing
                 if let Some(id) = &cls.ident {

crates/swc_ecma_minifier/src/compress/optimize/mod.rs

@@ -0,0 +1,14 @@
+class X {
+    constructor() {
+
+    }
+}
+
+class Y extends X {
+
+}
+
+const t = (a) => (b => {
+    if (a.foo()) throw Error();
+    return a;
+}), y = t(new Y);

crates/swc_ecma_minifier/tests/fixture/issues/11303/input.js

@@ -0,0 +1,4 @@
+class X {
+}
+new class extends X {
+};

crates/swc_ecma_minifier/tests/fixture/issues/11303/output.js

@@ -1,12 +1 @@
-Yp.revoke, (a)=>Yp.config({
-        aria: {
-            mode: "checked"
-        },
-        ...ge(a, (e, t)=>"exclusive" !== t),
-        onToggled: (c, d)=>{
-            p(a.onToggled) && a.onToggled(c, d), Or(c, th, {
-                item: c,
-                state: d
-            });
-        }
-    });
+Yp.revoke;

crates/swc_ecma_minifier/tests/fixture/next/tinymce/1/output.js

@@ -39,4 +39,4 @@
   "bugs": {
     "url": "https://github.com/swc-project/swc/issues"
   }
-}
+}