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fix(es/compat): Handle sparse arrays correctly in generator transforms (#11131)
**Description:** Transforms arrays with empty slots correctly. ```javascript function* generator() {yield [, 'hello']} ``` is transformed to: ```javascript // ... function generator() { return _ts_generator(this, function(_state) { switch(_state.label){ case 0: return [ 4, [ 'hello' ] ]; case 1: _state.sent(); return [ 2 ]; } }); } ``` instead of: ```javascript function gen() { return _ts_generator(this, function (_state) { switch (_state.label) { case 0: return [ 4, [ , 'hello' ] ]; case 1: _state.sent(); return [ 2 ]; } }); } ``` (playground [url](https://play.swc.rs/?version=1.13.20&code=H4sIAAAAAAAAA0srzUsuyczP01JIT81LLUosyS%2FS0FSorsxMzUlRiNZRUM9IzcnJV4%2BtBQBOVRuJKQAAAA%3D%3D&config=H4sIAAAAAAAAA1WPSw7DIAwF9zkF8rrbdtE79BAWdSIifrKJVBTl7iUE0maH3xsz8jooBbNoeKq1PMsQkYX4nEsi2Sf8lARIOxTNJia49XaWvRrRCtVoOxpIyBOluiX3hoMNQajjLXPGmzH%2FC3VwkUnkCu4o%2BsnSVTc0JbjwXmrZDkk50qF%2FwA%2FqsvNjMPLqm4kXGrYvhlQioBQBAAA%3D) with 1.13.20)
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+126
-8
lines changed

5 files changed

+126
-8
lines changed

‎.changeset/shiny-spiders-relax.md‎

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@@ -0,0 +1,6 @@
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---
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swc_ecma_compat_es2015: patch
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swc_core: patch
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---
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fix(es/compat): Handle sparse arrays correctly in generator transforms

‎crates/swc_ecma_compat_es2015/src/generator.rs‎

Lines changed: 38 additions & 8 deletions
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@@ -1112,7 +1112,7 @@ impl Generator {
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);
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}
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let expressions = elements
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let mut expressions = elements
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.iter_mut()
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.skip(num_initial_elements)
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.map(|v| v.take())
@@ -1128,7 +1128,17 @@ impl Generator {
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spread: None,
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expr: Box::new(Expr::Array(ArrayLit {
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span: DUMMY_SP,
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elems: expressions,
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elems: expressions
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.take()
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.into_iter()
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.map(|expr| match expr {
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Some(expr_or_spread) => match &*expr_or_spread.expr {
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Expr::Invalid(_) => None,
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_ => Some(expr_or_spread),
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},
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None => None,
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})
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.collect(),
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})),
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}],
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..Default::default()
@@ -1141,7 +1151,13 @@ impl Generator {
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.take()
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.into_iter()
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.map(Some)
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.chain(expressions)
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.chain(expressions.take().into_iter().map(|expr| match expr {
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Some(expr_or_spread) => match &*expr_or_spread.expr {
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Expr::Invalid(_) => None,
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_ => Some(expr_or_spread),
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},
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None => None,
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}))
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.collect(),
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}
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.into()
@@ -1173,7 +1189,17 @@ impl Generator {
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.as_callee(),
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args: vec![Box::new(Expr::Array(ArrayLit {
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span: DUMMY_SP,
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elems: expressions.take(),
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elems: expressions
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.take()
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.into_iter()
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.map(|expr| match expr {
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Some(expr_or_spread) => match &*expr_or_spread.expr {
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Expr::Invalid(_) => None,
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_ => Some(expr_or_spread),
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},
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None => None,
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})
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.collect(),
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}))
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.as_arg()],
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..Default::default()
@@ -1187,7 +1213,13 @@ impl Generator {
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.take()
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.into_iter()
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.map(Some)
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.chain(expressions.take())
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.chain(expressions.take().into_iter().map(|expr| match expr {
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Some(expr_or_spread) => match &*expr_or_spread.expr {
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Expr::Invalid(_) => None,
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_ => Some(expr_or_spread),
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},
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None => None,
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}))
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.collect(),
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}
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.into(),
@@ -1199,9 +1231,7 @@ impl Generator {
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}
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element.visit_mut_with(self);
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if element.is_some() {
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expressions.push(element);
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}
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expressions.push(element);
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expressions
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}
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‎crates/swc_ecma_transforms_compat/tests/__swc_snapshots__/tests/es2015_generator_sparse_array.rs/sparse_array_leading_hole.js‎

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@@ -0,0 +1,19 @@
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function gen() {
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return _ts_generator(this, function (_state) {
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switch (_state.label) {
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case 0:
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return [
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4,
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[
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,
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'hello'
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]
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];
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case 1:
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_state.sent();
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return [
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2
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];
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}
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});
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}

‎crates/swc_ecma_transforms_compat/tests/__swc_snapshots__/tests/es2015_generator_sparse_array.rs/sparse_array_middle_hole.js‎

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@@ -0,0 +1,20 @@
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function gen() {
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return _ts_generator(this, function (_state) {
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switch (_state.label) {
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case 0:
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return [
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4,
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[
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'start',
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,
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'end'
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]
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];
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case 1:
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_state.sent();
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return [
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2
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];
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}
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});
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}

‎crates/swc_ecma_transforms_compat/tests/es2015_generator_sparse_array.rs‎

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#![allow(clippy::unit_arg)]
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use swc_common::{comments::NoopComments, Mark};
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use swc_ecma_ast::Pass;
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use swc_ecma_parser::Syntax;
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use swc_ecma_transforms_base::resolver;
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use swc_ecma_transforms_compat::es2015::generator::generator;
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use swc_ecma_transforms_testing::test;
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fn syntax() -> Syntax {
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Syntax::default()
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}
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fn tr(_: ()) -> impl Pass {
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let unresolved_mark = Mark::new();
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let top_level_mark = Mark::new();
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(
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resolver(unresolved_mark, top_level_mark, false),
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generator(unresolved_mark, NoopComments),
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)
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}
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test!(
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syntax(),
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|_| tr(Default::default()),
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sparse_array_leading_hole,
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r#"
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function* gen() {
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yield [, 'hello'];
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}
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"#
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);
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test!(
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syntax(),
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|_| tr(Default::default()),
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sparse_array_middle_hole,
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r#"
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function* gen() {
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yield ['start', , 'end'];
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}
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"#
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);

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