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fix(minifier): avoid merging side effectful expressions to next assignment statement if the side effect may change the left hand side reference #16165

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Merged
merged 1 commit into from
Nov 27, 2025
Merged

fix(minifier): avoid merging side effectful expressions to next assignment statement if the side effect may change the left hand side reference #16165

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31 changes: 16 additions & 15 deletions apps/oxlint/src-js/generated/deserialize.js
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Original file line number Diff line number Diff line change
Expand Up @@ -4991,21 +4991,22 @@ function deserializeTSModuleDeclaration(pos) {
} else {
let innerId = body.id;
if (innerId.type === "Identifier") {
let start, end;
id.parent =
innerId.parent =
node.id =
parent =
{
__proto__: NodeProto,
type: "TSQualifiedName",
left: id,
right: innerId,
start: (start = id.start),
end: (end = innerId.end),
range: [start, end],
parent: node,
};
let start,
end,
outerId =
(node.id =
parent =
{
__proto__: NodeProto,
type: "TSQualifiedName",
left: id,
right: innerId,
start: (start = id.start),
end: (end = innerId.end),
range: [start, end],
parent: node,
});
id.parent = innerId.parent = outerId;
} else {
// Replace `left` of innermost `TSQualifiedName` with a nested `TSQualifiedName` with `id` of
// this module on left, and previous `left` of innermost `TSQualifiedName` on right
Expand Down
47 changes: 47 additions & 0 deletions crates/oxc_minifier/src/peephole/minimize_statements.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1384,6 +1384,38 @@ impl<'a> PeepholeOptimizations {
// ```
return Some(false);
}
if replacement_has_side_effect {
// If the assignment target may depend on side effects of the replacement,
// don't reorder it past the assignment target. The non-last part of the
// assignment target is evaluated before the assignment evaluation so that
// part may be changed by the side effect. For example, "fn()" may change
// "foo" here:
// ```js
// let a = fn();
// foo.bar = a;
// ```
let may_depend_on_side_effect = match &assign_expr.left {
AssignmentTarget::AssignmentTargetIdentifier(_) => false,
AssignmentTarget::ComputedMemberExpression(member_expr) => {
Self::is_expression_that_reference_may_change(&member_expr.object, ctx)
}
AssignmentTarget::PrivateFieldExpression(member_expr) => {
Self::is_expression_that_reference_may_change(&member_expr.object, ctx)
}
AssignmentTarget::StaticMemberExpression(member_expr) => {
Self::is_expression_that_reference_may_change(&member_expr.object, ctx)
}
AssignmentTarget::ArrayAssignmentTarget(_)
| AssignmentTarget::ObjectAssignmentTarget(_)
| AssignmentTarget::TSAsExpression(_)
| AssignmentTarget::TSNonNullExpression(_)
| AssignmentTarget::TSSatisfiesExpression(_)
| AssignmentTarget::TSTypeAssertion(_) => true,
};
if may_depend_on_side_effect {
return Some(false);
}
}
// If we get here then it should be safe to attempt to substitute the
// replacement past the left operand into the right operand.
if let Some(changed) = Self::substitute_single_use_symbol_in_expression(
Expand Down Expand Up @@ -1799,6 +1831,21 @@ impl<'a> PeepholeOptimizations {
// Otherwise we should stop trying to substitute past this point
Some(false)
}

fn is_expression_that_reference_may_change(expr: &Expression<'a>, ctx: &Ctx<'a, '_>) -> bool {
match expr {
Expression::Identifier(id) => {
if let Some(symbol_id) = ctx.scoping().get_reference(id.reference_id()).symbol_id()
{
ctx.scoping().symbol_is_mutated(symbol_id)
} else {
true
}
}
Expression::ThisExpression(_) => false,
_ => true,
}
}
}

#[cfg(test)]
Expand Down
19 changes: 19 additions & 0 deletions crates/oxc_minifier/tests/peephole/inline_single_use_variable.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -222,6 +222,25 @@ fn test_inline_single_use_variable() {
"function wrapper() { var __proto__ = []; return { __proto__ } }",
"function wrapper() { return { ['__proto__']: [] } }",
);

// cannot be compressed to `function wrapper() { var foo; globalThis[console.log(foo)] = (() => { foo = 1 })() }`
test(
"function wrapper() { var foo; var bar = (() => { foo = 1 })(); globalThis[console.log(foo)] = bar }",
"function wrapper() { var foo, bar = (() => { foo = 1 })(); globalThis[console.log(foo)] = bar }",
);
// cannot be compressed to `function wrapper() { let foo; return foo.bar = (() => { foo = {} })(), foo }`
test(
"function wrapper() { let foo; const bar = (() => { foo = {} })(); foo.bar = bar; return foo }",
"function wrapper() { let foo, bar = (() => { foo = {} })(); return foo.bar = bar, foo }",
);
test(
"function wrapper() { let foo = {}; const bar = (() => { console.log() })(); foo.bar = bar; return foo }",
"function wrapper() { let foo = {}; return foo.bar = (() => { console.log() })(), foo }",
);
test(
"function wrapper() { const bar = (() => { console.log() })(); this.bar = bar; return this }",
"function wrapper() { return this.bar = (() => { console.log() })(), this }",
);
}

#[test]
Expand Down
12 changes: 6 additions & 6 deletions napi/parser/generated/deserialize/js_parent.js
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Original file line number Diff line number Diff line change
Expand Up @@ -4346,10 +4346,9 @@ function deserializeTSModuleDeclaration(pos) {
body.parent = node;
} else {
let innerId = body.id;
if (innerId.type === "Identifier")
id.parent =
innerId.parent =
node.id =
if (innerId.type === "Identifier") {
let outerId =
(node.id =
parent =
{
type: "TSQualifiedName",
Expand All @@ -4358,8 +4357,9 @@ function deserializeTSModuleDeclaration(pos) {
start: id.start,
end: innerId.end,
parent: node,
};
else {
});
id.parent = innerId.parent = outerId;
} else {
// Replace `left` of innermost `TSQualifiedName` with a nested `TSQualifiedName` with `id` of
// this module on left, and previous `left` of innermost `TSQualifiedName` on right
node.id = innerId;
Expand Down
29 changes: 15 additions & 14 deletions napi/parser/generated/deserialize/js_range_parent.js
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Original file line number Diff line number Diff line change
Expand Up @@ -4560,20 +4560,21 @@ function deserializeTSModuleDeclaration(pos) {
} else {
let innerId = body.id;
if (innerId.type === "Identifier") {
let start, end;
id.parent =
innerId.parent =
node.id =
parent =
{
type: "TSQualifiedName",
left: id,
right: innerId,
start: (start = id.start),
end: (end = innerId.end),
range: [start, end],
parent: node,
};
let start,
end,
outerId =
(node.id =
parent =
{
type: "TSQualifiedName",
left: id,
right: innerId,
start: (start = id.start),
end: (end = innerId.end),
range: [start, end],
parent: node,
});
id.parent = innerId.parent = outerId;
} else {
// Replace `left` of innermost `TSQualifiedName` with a nested `TSQualifiedName` with `id` of
// this module on left, and previous `left` of innermost `TSQualifiedName` on right
Expand Down
12 changes: 6 additions & 6 deletions napi/parser/generated/deserialize/ts_parent.js
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Original file line number Diff line number Diff line change
Expand Up @@ -4604,10 +4604,9 @@ function deserializeTSModuleDeclaration(pos) {
body.parent = node;
} else {
let innerId = body.id;
if (innerId.type === "Identifier")
id.parent =
innerId.parent =
node.id =
if (innerId.type === "Identifier") {
let outerId =
(node.id =
parent =
{
type: "TSQualifiedName",
Expand All @@ -4616,8 +4615,9 @@ function deserializeTSModuleDeclaration(pos) {
start: id.start,
end: innerId.end,
parent: node,
};
else {
});
id.parent = innerId.parent = outerId;
} else {
// Replace `left` of innermost `TSQualifiedName` with a nested `TSQualifiedName` with `id` of
// this module on left, and previous `left` of innermost `TSQualifiedName` on right
node.id = innerId;
Expand Down
29 changes: 15 additions & 14 deletions napi/parser/generated/deserialize/ts_range_parent.js
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Original file line number Diff line number Diff line change
Expand Up @@ -4825,20 +4825,21 @@ function deserializeTSModuleDeclaration(pos) {
} else {
let innerId = body.id;
if (innerId.type === "Identifier") {
let start, end;
id.parent =
innerId.parent =
node.id =
parent =
{
type: "TSQualifiedName",
left: id,
right: innerId,
start: (start = id.start),
end: (end = innerId.end),
range: [start, end],
parent: node,
};
let start,
end,
outerId =
(node.id =
parent =
{
type: "TSQualifiedName",
left: id,
right: innerId,
start: (start = id.start),
end: (end = innerId.end),
range: [start, end],
parent: node,
});
id.parent = innerId.parent = outerId;
} else {
// Replace `left` of innermost `TSQualifiedName` with a nested `TSQualifiedName` with `id` of
// this module on left, and previous `left` of innermost `TSQualifiedName` on right
Expand Down
6 changes: 3 additions & 3 deletions tasks/minsize/minsize.snap
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Original file line number Diff line number Diff line change
Expand Up @@ -17,11 +17,11 @@ Original | minified | minified | gzip | gzip | Iterations | Fi

1.25 MB | 642.64 kB | 646.76 kB | 159.40 kB | 163.73 kB | 2 | three.js

2.14 MB | 711.13 kB | 724.14 kB | 160.42 kB | 181.07 kB | 2 | victory.js
2.14 MB | 711.14 kB | 724.14 kB | 160.43 kB | 181.07 kB | 2 | victory.js

3.20 MB | 1.00 MB | 1.01 MB | 322.59 kB | 331.56 kB | 3 | echarts.js

6.69 MB | 2.22 MB | 2.31 MB | 458.41 kB | 488.28 kB | 4 | antd.js
6.69 MB | 2.22 MB | 2.31 MB | 458.43 kB | 488.28 kB | 4 | antd.js

10.95 MB | 3.33 MB | 3.49 MB | 853.34 kB | 915.50 kB | 4 | typescript.js
10.95 MB | 3.33 MB | 3.49 MB | 853.36 kB | 915.50 kB | 4 | typescript.js

4 changes: 2 additions & 2 deletions tasks/track_memory_allocations/allocs_minifier.snap
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Original file line number Diff line number Diff line change
Expand Up @@ -6,9 +6,9 @@ cal.com.tsx | 1.06 MB || 40453 | 3033 |

RadixUIAdoptionSection.jsx | 2.52 kB || 85 | 9 || 30 | 6

pdf.mjs | 567.30 kB || 20494 | 2899 || 47442 | 7725
pdf.mjs | 567.30 kB || 20495 | 2899 || 47447 | 7728

antd.js | 6.69 MB || 99524 | 13523 || 331583 | 69338
antd.js | 6.69 MB || 99534 | 13524 || 331657 | 69358

binder.ts | 193.08 kB || 4760 | 974 || 7075 | 824

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