From 405b73d8e72b92fb329d777dd157c78decf4f5c2 Mon Sep 17 00:00:00 2001
From: Boshen <1430279+Boshen@users.noreply.github.com>
Date: Thu, 16 Jan 2025 03:08:26 +0000
Subject: [PATCH] fix(minifier): do not change `delete undefined` to `delete
 void 0` (#8527)

`delete undefined` returns `false`
`delete void 0` returns `true`
---
 .../ast_passes/peephole_substitute_alternate_syntax.rs   | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/crates/oxc_minifier/src/ast_passes/peephole_substitute_alternate_syntax.rs b/crates/oxc_minifier/src/ast_passes/peephole_substitute_alternate_syntax.rs
index a8f8939fac6d4..de73732b0a357 100644
--- a/crates/oxc_minifier/src/ast_passes/peephole_substitute_alternate_syntax.rs
+++ b/crates/oxc_minifier/src/ast_passes/peephole_substitute_alternate_syntax.rs
@@ -250,6 +250,12 @@ impl<'a, 'b> PeepholeSubstituteAlternateSyntax {
         if !ctx.is_identifier_undefined(ident) {
             return None;
         }
+        // `delete undefined` returns `false`
+        // `delete void 0` returns `true`
+        if matches!(ctx.parent(), Ancestor::UnaryExpressionArgument(e) if e.operator().is_delete())
+        {
+            return None;
+        }
         Some(ctx.ast.void_0(ident.span))
     }
 
@@ -1297,6 +1303,9 @@ mod test {
         // destructuring throw error side effect
         test_same("var {} = void 0");
         test_same("var [] = void 0");
+        // `delete undefined` returns `false`
+        // `delete void 0` returns `true`
+        test_same("delete undefined");
     }
 
     #[test]