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fix(es/minifier): preserve lexical method defaults (#12239)
**Description:** Fix object method-to-arrow conversion when a parameter default references lexical `arguments` or `super`. - Reject conversion for those parameter initializers, preserving method bindings and valid `super` syntax. - Add an SWC-owned #12187 fixture with runtime coverage for both unsafe defaults, existing body controls, and a safe default that still converts to an arrow. - Add patch changesets for `swc_ecma_minifier` and `swc_core`. **BREAKING CHANGE:** None. **Related issue (if exists):** Closes #12187 **Tests:** - `UPDATE=1 cargo test -p swc_ecma_minifier` - `cargo test -p swc_ecma_minifier` - `crates/swc_ecma_minifier/scripts/test.sh` - `crates/swc_ecma_minifier/scripts/exec.sh` - `cargo fmt --all` - `cargo clippy --all --all-targets -- -D warnings` --------- Co-authored-by: Labor0 Bot <279936132+labor0-bot[bot]@users.noreply.github.com>
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‎.changeset/fix-minifier-lexical-defaults.md‎

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---
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swc_core: patch
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swc_ecma_minifier: patch
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---
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fix(es/minifier): Preserve lexical arguments and super in method parameter defaults

‎crates/swc_ecma_minifier/src/compress/pure/arrows.rs‎

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use swc_common::{util::take::Take, DUMMY_SP};
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use swc_ecma_ast::*;
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use swc_ecma_transforms_base::rename::contains_eval;
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use swc_ecma_utils::{contains_arguments, contains_this_expr};
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use super::Pure;
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if m.function.is_generator
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|| contains_arguments(&m.function.body)
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|| contains_super(&m.function.body)
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|| m.function.params.iter().any(contains_this_expr)
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|| m.function.params.iter().any(|param| {
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contains_this_expr(param)
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|| contains_arguments(param)
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|| contains_super(param)
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|| contains_eval(param, false)
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})
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{
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return;
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}

‎crates/swc_ecma_minifier/tests/fixture/issues/12187/config.json‎

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{
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"defaults": true
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}

‎crates/swc_ecma_minifier/tests/fixture/issues/12187/expected.stdout‎

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0 0 7 0 7 5

‎crates/swc_ecma_minifier/tests/fixture/issues/12187/input.js‎

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function argumentsDefault() {
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if (arguments.length !== 2) {
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throw new Error("arguments were dropped");
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}
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return {
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m(value = arguments.length) {
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return value;
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},
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}.m();
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}
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function evalDefault() {
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if (arguments.length !== 2) {
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throw new Error("arguments were dropped");
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}
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return {
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m(value = eval("arguments.length")) {
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return value;
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},
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}.m();
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}
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const superDefault = {
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__proto__: {
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value: 7,
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},
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m(value = super.value) {
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return value;
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},
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};
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function argumentsBody() {
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return {
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m() {
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return arguments.length;
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},
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}.m();
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}
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const superBody = {
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__proto__: {
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value: 7,
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},
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m() {
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return super.value;
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},
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};
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const safeDefault = {
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m(value = 5) {
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return value;
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},
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};
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console.log(
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argumentsDefault(1, 2),
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evalDefault(1, 2),
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superDefault.m(),
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argumentsBody(1, 2),
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superBody.m(),
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safeDefault.m(),
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);

‎crates/swc_ecma_minifier/tests/fixture/issues/12187/output.js‎

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function argumentsDefault() {
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if (2 != arguments.length) throw Error("arguments were dropped");
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return ({
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m (value = arguments.length) {
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return value;
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}
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}).m();
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}
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function evalDefault() {
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if (2 != arguments.length) throw Error("arguments were dropped");
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return ({
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m (value = eval("arguments.length")) {
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return value;
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}
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}).m();
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}
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const superDefault = {
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__proto__: {
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value: 7
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},
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m (value = super.value) {
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return value;
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}
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};
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function argumentsBody() {
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return ({
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m () {
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return arguments.length;
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}
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}).m();
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}
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const superBody = {
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__proto__: {
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value: 7
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},
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m () {
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return super.value;
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}
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}, safeDefault = {
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m: (value = 5)=>value
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};
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console.log(argumentsDefault(1, 2), evalDefault(1, 2), superDefault.m(), argumentsBody(1, 2), superBody.m(), safeDefault.m());

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