From 2a10a99444eb59fa44ce730baff5323ec3b418b7 Mon Sep 17 00:00:00 2001
From: sapphi-red <49056869+sapphi-red@users.noreply.github.com>
Date: Mon, 10 Feb 2025 05:36:13 +0000
Subject: [PATCH] feat(ecmascript): support arrays and objects for unary
 expression may_have_side_effects (#8990)

Detect `+[]` / `+{}` as side effect free.
---
 .../src/side_effects/may_have_side_effects.rs        | 12 ++++++++++++
 .../tests/ecmascript/may_have_side_effects.rs        |  6 ++++++
 2 files changed, 18 insertions(+)

diff --git a/crates/oxc_ecmascript/src/side_effects/may_have_side_effects.rs b/crates/oxc_ecmascript/src/side_effects/may_have_side_effects.rs
index a26c1db78a198..82b6a89071576 100644
--- a/crates/oxc_ecmascript/src/side_effects/may_have_side_effects.rs
+++ b/crates/oxc_ecmascript/src/side_effects/may_have_side_effects.rs
@@ -82,6 +82,12 @@ pub trait MayHaveSideEffects {
                         !(matches!(ident.name.as_str(), "Infinity" | "NaN" | "undefined")
                             && self.is_global_reference(ident))
                     }
+                    Expression::ArrayExpression(arr) => {
+                        self.array_expression_may_have_side_effects(arr)
+                    }
+                    // unless `Symbol.toPrimitive`, `valueOf`, `toString` is overridden,
+                    // ToPrimitive for an object returns `"[object Object]"`
+                    Expression::ObjectExpression(obj) => !obj.properties.is_empty(),
                     // ToNumber throws an error when the argument is Symbol / BigInt / an object that
                     // returns Symbol or BigInt from ToPrimitive
                     _ => true,
@@ -98,6 +104,12 @@ pub trait MayHaveSideEffects {
                         !(matches!(ident.name.as_str(), "Infinity" | "NaN" | "undefined")
                             && self.is_global_reference(ident))
                     }
+                    Expression::ArrayExpression(arr) => {
+                        self.array_expression_may_have_side_effects(arr)
+                    }
+                    // unless `Symbol.toPrimitive`, `valueOf`, `toString` is overridden,
+                    // ToPrimitive for an object returns `"[object Object]"`
+                    Expression::ObjectExpression(obj) => !obj.properties.is_empty(),
                     // ToNumber throws an error when the argument is Symbol an object that
                     // returns Symbol from ToPrimitive
                     _ => true,
diff --git a/crates/oxc_minifier/tests/ecmascript/may_have_side_effects.rs b/crates/oxc_minifier/tests/ecmascript/may_have_side_effects.rs
index 895cd346d75d7..2e22929a55c3c 100644
--- a/crates/oxc_minifier/tests/ecmascript/may_have_side_effects.rs
+++ b/crates/oxc_minifier/tests/ecmascript/may_have_side_effects.rs
@@ -364,9 +364,12 @@ fn test_unary_expressions() {
     test_with_global_variables("+Infinity", vec!["Infinity".to_string()], false);
     test_with_global_variables("+NaN", vec!["NaN".to_string()], false);
     test_with_global_variables("+undefined", vec!["undefined".to_string()], false); // NaN
+    test("+[]", false); // 0
+    test("+[foo()]", true);
     test("+foo()", true);
     test("+foo", true); // foo can be Symbol or BigInt
     test("+Symbol()", true);
+    test("+{}", false); // NaN
     test("+{ valueOf() { return Symbol() } }", true);
 
     test("-0", false);
@@ -377,9 +380,12 @@ fn test_unary_expressions() {
     test_with_global_variables("-Infinity", vec!["Infinity".to_string()], false);
     test_with_global_variables("-NaN", vec!["NaN".to_string()], false);
     test_with_global_variables("-undefined", vec!["undefined".to_string()], false); // NaN
+    test("-[]", false); // -0
+    test("-[foo()]", true);
     test("-foo()", true);
     test("-foo", true); // foo can be Symbol
     test("-Symbol()", true);
+    test("-{}", false); // NaN
     test("-{ valueOf() { return Symbol() } }", true);
 
     test("~0", false);