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fix(minifier): recognize object spread of object literals as side-effect-free #20299

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graphite-app merged 1 commit into from
Mar 13, 2026
+23 −4
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fix(minifier): recognize object spread of object literals as side-effect-free #20299

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4 changes: 4 additions & 0 deletions crates/oxc_ecmascript/src/side_effects/expressions.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -650,6 +650,10 @@ impl<'a> MayHaveSideEffects<'a> for ObjectPropertyKind<'a> {
} else {
match &e.argument {
Expression::ArrayExpression(arr) => arr.may_have_side_effects(ctx),
Expression::ObjectExpression(obj) => obj
.properties
.iter()
.any(|property| property.may_have_side_effects(ctx)),
Comment on lines +653 to +656
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@chatgpt-codex-connector chatgpt-codex-connector bot Mar 13, 2026

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P1 Badge Treat getter-backed object spreads as side-effectful

When property_read_side_effects is All (the default), spreading an object literal with accessor properties must be considered effectful because object spread performs a property read (Get) for each enumerable key. This new branch only checks property.may_have_side_effects(ctx), which does not account for PropertyKind::Get, so expressions like ({...{ get a() { foo() } }}) can be misclassified as side-effect-free and then removed by remove_unused_object_expr, dropping the getter invocation.

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Expression::StringLiteral(_) => false,
Expression::TemplateLiteral(t) => t.may_have_side_effects(ctx),
_ => true,
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7 changes: 6 additions & 1 deletion crates/oxc_minifier/src/peephole/remove_unused_expression.rs
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Expand Up @@ -336,7 +336,12 @@ impl<'a> PeepholeOptimizations {
return true;
}
if object_expr.properties.iter().all(ObjectPropertyKind::is_spread) {
return false;
// All-spread objects like `({...x})` can only be removed if
// the spread arguments themselves have no side effects.
return !object_expr
.properties
.iter()
.any(|property| property.may_have_side_effects(ctx));
}

let mut transformed_elements = ctx.ast.vec();
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12 changes: 9 additions & 3 deletions crates/oxc_minifier/tests/ecmascript/may_have_side_effects.rs
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Expand Up @@ -310,10 +310,11 @@ fn closure_compiler_tests() {
test("new Object(...true)", true);

// OBJECT_SPREAD
// These could all invoke getters.
// Spreading unknown identifiers could invoke getters.
test("({...x})", true);
test("({...{}})", true);
test("({...{a:1}})", true);
// Spreading object literals is side-effect-free if the properties are.
test("({...{}})", false);
test("({...{a:1}})", false);
test("({...{a:i++}})", true);
test("({...{a:f()}})", true);
test("({...f()})", true);
Expand Down Expand Up @@ -711,6 +712,11 @@ fn test_object_expression() {
test("({...`foo${foo}`})", true);
test("({...`foo${foo()}`})", true);
test("({...foo()})", true);
// Spreading object literals
test("({...{}})", false);
test("({...{a: 1}})", false);
test("({...{a: foo()}})", true);
test("({...{[foo()]: 1}})", true);
}

#[test]
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4 changes: 4 additions & 0 deletions crates/oxc_minifier/tests/peephole/remove_unused_expression.rs
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Expand Up @@ -176,6 +176,10 @@ fn test_object_literal() {
// Object-spread may trigger getters.
test_same("({...a})");
test_same("({...foo()})");
// Spreading object literals is safe if contents are safe.
test("({...{}})", "");
test("({...{a: 1}})", "");
test("({...{a: foo()}})", "foo()");
test("({ [{ foo: foo() }]: 0 })", "foo()");
test("({ foo: { foo: foo() } })", "foo()");

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