feat: implement Iterator.zip and Iterator.zipKeyed (#4564) by yush-1018 · Pull Request #4946 · boa-dev/boa

yush-1018 · 2026-03-08T07:47:40Z

Implements the TC39 Joint Iteration proposal (#4564).

Adds Iterator.zip and Iterator.zipKeyed static methods with support for
"shortest", "longest", and "strict" modes. Includes a new ZipIterator
backing object with proper iterator protocol handling.

github-actions · 2026-03-08T07:58:10Z

Test262 conformance changes

Test result	main count	PR count	difference
Total	52,963	52,963	0
Passed	50,073	50,073	0
Ignored	2,072	2,072	0
Failed	818	818	0
Panics	0	0	0
Conformance	94.54%	94.54%	0.00%

Tested main commit: 055ee0958ce332f3f99af27536a7c6f9a91def27
Tested PR commit: 455af3a0d140f320fa6877fb11aa665825857998
Compare commits: 055ee09...455af3a

nekevss

Please look at some other built-in for general style on implementation.

Most steps should have some level of documentation. There's a lot of nesting here and it's not clear whether it's a result of the specification or can be improved in another way.

nekevss · 2026-03-08T20:31:08Z

core/engine/src/builtins/iterable/mod.rs

+        let iterables = args.get_or_undefined(0);
+        let options = args.get_or_undefined(1);
+
+        // 1. If iterables is not an Object, throw a TypeError exception.


issue: include the entire specification text.

nekevss · 2026-03-08T20:36:24Z

core/engine/src/builtins/iterable/mod.rs

+        let mode = Self::parse_zip_mode(options, context)?;
+
+        // 6-7. Parse padding option (only for "longest" mode).
+        let padding_option = if mode == ZipMode::Longest {


suggestion: rewrite these using some if-let chains

nekevss · 2026-03-08T20:39:36Z

core/engine/src/builtins/iterable/mod.rs

+        let mode = Self::parse_zip_mode(options, context)?;
+
+        // 6-7. Parse padding option.
+        let padding_option = if mode == ZipMode::Longest {


suggestion: use if-let chains here

nekevss · 2026-03-08T20:40:47Z

core/engine/src/builtins/iterable/zip_iterator.rs

+    }
+}
+
+impl IntrinsicObject for ZipIterator {


nit: move this higher up in the file

yush-1018 · 2026-03-10T20:03:58Z

Hey @nekevss,

All review feedback addressed! (Added spec comments, refactored padding parsing with if let, and moved the IntrinsicObject impl).

Ready for review.

Thanks!

jedel1043 · 2026-03-13T06:24:34Z

All the implementation needs to be gated behind the experimental feature, since the proposal hasn't reached stage 4

yush-1018 · 2026-03-18T13:05:41Z

Can you please review this once.

Thanks!

jedel1043 · 2026-03-18T13:39:06Z

core/engine/src/builtins/typed_array/builtin.rs

Unrelated change

jedel1043 · 2026-03-18T13:39:16Z

core/engine/src/builtins/typed_array/tests.rs

Also unrelated

jedel1043 · 2026-03-18T13:39:24Z

core/engine/src/module/loader/mod.rs

Unrelated...

jedel1043 · 2026-03-18T13:42:47Z

Also you didn't address some of Kevin's comments

codecov · 2026-03-18T22:26:26Z

Codecov Report

❌ Patch coverage is 82.05882% with 61 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.97%. Comparing base (6ddc2b4) to head (b1e8393).
⚠️ Report is 917 commits behind head on main.

Files with missing lines	Patch %	Lines
...gine/src/builtins/iterable/iterator_constructor.rs	73.61%	43 Missing ⚠️
core/engine/src/builtins/iterable/zip_iterator.rs	89.59%	18 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #4946       +/-   ##
===========================================
+ Coverage   47.24%   59.97%   +12.73%     
===========================================
  Files         476      583      +107     
  Lines       46892    63798    +16906     
===========================================
+ Hits        22154    38266    +16112     
- Misses      24738    25532      +794

☔ View full report in Codecov by Sentry.
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yush-1018 · 2026-03-19T08:14:08Z

PR is ready to review.

Thanks!

nekevss · 2026-03-21T21:35:46Z

Looks like there may be some conflicts that need to be resolved

…nsic

…type chain, add tests

github-actions · 2026-03-22T13:09:58Z

Test262 conformance changes

Test result	main count	PR count	difference
Total	52,963	52,963	0
Passed	50,545	50,545	0
Ignored	1,426	1,426	0
Failed	992	992	0
Panics	2	2	0
Conformance	95.43%	95.43%	0.00%

Tested main commit: 817b6eaade662a49434c5d295667068a4875b378
Tested PR commit: b1e8393b198609caf94b910fc92e53a6478f6874
Compare commits: 817b6ea...b1e8393

yush-1018 · 2026-03-22T18:16:07Z

PR is ready to merge.

Thanks!

jedel1043 · 2026-03-23T17:55:47Z

Marking as blocked on #5236, since that PR would remove a lot of the boilerplate code in this PR.

yush-1018 requested a review from a team as a code owner March 8, 2026 07:47

jedel1043 added the C-Builtins PRs and Issues related to builtins/intrinsics label Mar 8, 2026

nekevss requested changes Mar 8, 2026

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jedel1043 added A-Enhancement New feature or request Waiting On Author Waiting on PR changes from the author labels Mar 13, 2026

github-actions bot added the Waiting On Review Waiting on reviews from the maintainers label Mar 17, 2026

yush-1018 marked this pull request as draft March 17, 2026 09:01

yush-1018 force-pushed the feat/joint-iteration-clean branch from 99be867 to cc4de18 Compare March 17, 2026 17:59

github-actions bot added the C-Tests Issues and PRs related to the tests. label Mar 18, 2026

yush-1018 marked this pull request as ready for review March 18, 2026 13:04

jedel1043 reviewed Mar 18, 2026

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core/engine/src/builtins/typed_array/builtin.rs

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Unrelated change

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jedel1043 reviewed Mar 18, 2026

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core/engine/src/builtins/typed_array/tests.rs

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Also unrelated

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core/engine/src/module/loader/mod.rs

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Unrelated...

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jedel1043 removed the Waiting On Review Waiting on reviews from the maintainers label Mar 18, 2026

yush-1018 force-pushed the feat/joint-iteration-clean branch from 2612098 to 0993de3 Compare March 18, 2026 21:11

yush-1018 added 7 commits March 22, 2026 14:38

feat: implement Iterator.zip and Iterator.zipKeyed (boa-dev#4564)

49dd95a

fix(builtins): address PR feedback for Iterator.zip

03cc3fa

refactor: gate Iterator.zip/zipKeyed behind experimental feature

9f4962f

fix: resolve CI failures by addressing clippy, fmt, and missing intri…

c859d50

…nsic

fix(lint): replace forbidden unwrap usages with expect

4abc0d3

style: run cargo fmt

b317691

fix(lint): use inspect_err instead of map_err

4bb9ae2

yush-1018 added 4 commits March 22, 2026 14:41

style: cargo fmt run

bfc5183

fix: resolve clippy redundant closure and use cow_utils for MSRV

0977571

fix(clippy): resolve ptr_arg and doc_markdown lints

db691c8

fix: move Iterator.zip/zipKeyed to constructor, fix ZipIterator proto…

293b797

…type chain, add tests

yush-1018 force-pushed the feat/joint-iteration-clean branch from 455af3a to 4f4cca1 Compare March 22, 2026 09:45

style: cargo fmt run for zip iterator

b1e8393

yush-1018 force-pushed the feat/joint-iteration-clean branch from 4f4cca1 to b1e8393 Compare March 22, 2026 13:00

jedel1043 added the Blocked Waiting for another code change label Mar 23, 2026

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