feat(transformer): warn top level await usage if not supported #14276

Copilot · 2025-10-01T11:49:36Z

Implementation Complete: Add warning for top-level await usage

Successfully implemented warning for top-level await usage when the target doesn't support it, following the same pattern as the existing BigInt warning.

✅ Successfully merged main branch and resolved all conflicts

All changes have been merged with the latest main and all tests pass. Ready for review and merge.

Summary

Test Results

All tests pass successfully:

✅ oxc_transformer: 30 unit tests + 3 integration tests (es_target)
✅ oxc_compat: 3 tests
✅ No clippy warnings
✅ Successfully merged with latest main

Resolved Conflicts

Merged with main and resolved conflicts in:

crates/oxc_compat/src/es_features.rs - kept both ES2020ArbitraryModuleNamespaceNames and ES2022TopLevelAwait features
crates/oxc_transformer/src/lib.rs - kept both import/export specifier methods and await expression method
crates/oxc_transformer/tests/integrations/es_target.rs - kept both test cases
crates/oxc_transformer/tests/integrations/snapshots/es_target.snap - updated test numbering to include both features
tasks/compat_data/data.json - kept both ArbitraryModuleNamespaceNames and TopLevelAwait entries

Fixes #14258

Original prompt

This section details on the original issue you should resolve

<issue_title>transformer: warn top level await usage if not supported</issue_title>
<issue_description>A warning is emitted when BigInt is used and the target does not support it (playground). Similar to that, it would be helpful if a warning is emitted for top-level await as well.</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #14258

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graphite-app · 2025-10-01T11:49:43Z

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crates/oxc_compat/src/es_features.rs

crates/oxc_transformer/src/es2022/mod.rs

codspeed-hq · 2025-10-02T04:35:11Z

CodSpeed Performance Report

Merging #14276 will not alter performance

_{Comparing copilot/fix-84bb58e5-a448-42e9-bd15-4c860fd78a4e (c2fd474) with main (8b14ec9)}

Summary

✅ 33 untouched
⏩ 4 skipped¹

4 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

sapphi-red · 2025-10-03T15:11:49Z

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feat(transformer): warn top level await usage if not supported #14276 👈 (View in Graphite)
feat(tasks/compat_data): add custom compat data for export namespace from #14317 : 1 other dependent PR (#14277 )
main

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fixed

crates/oxc_transformer/src/es2022/mod.rs

Co-authored-by: sapphi-red <49056869+sapphi-red@users.noreply.github.com>

…pLevelAwait to es-features.js Co-authored-by: sapphi-red <49056869+sapphi-red@users.noreply.github.com>

Co-authored-by: Dunqing <29533304+Dunqing@users.noreply.github.com>

…ier names (#15035) feat(transformer): add warning for arbitrary module namespace identifier names Implements warnings for the ES2020 "Arbitrary module namespace identifier names" feature (TC39 proposal #2154), which allows string literals as import/export specifiers. Similar to #14276. ### Changes - **Compatibility data**: Added `ArbitraryModuleNamespaceNames` to `tasks/compat_data/custom-compat-data.js` with browser support (Chrome 88+, Edge 88+, Opera 74+, Firefox 87+, Safari 14.1+, Node 16.0+, Deno 1.6+) - **Transformer**: Added warning logic in `ES2020` for string literals in `ImportSpecifier`, `ExportSpecifier`, and `ExportAllDeclaration` nodes - **Configuration**: Added `arbitrary_module_namespace_names` option and environment target mapping ### Example ```javascript // Triggers warning when targeting ES2019 or Chrome 87 export { foo as "kebab-case-name" }; import { "string-name" as bar } from "./module"; export * as "namespace" from "./module"; ``` Warning message: ``` ⚠ Arbitrary module namespace identifier names are not available in the configured target environment. ``` ### Testing Added integration tests covering supported/unsupported targets, multiple literals, and normal identifiers.  <details> <summary>Original prompt</summary> > Similar to #14276, add a warning for "Arbitrary module namespace identifier names" feature (tc39/ecma262#2154). Add the compat data to `tasks/compat_data/custom-compat-data.js` as the data is not included in the compat table. </details>  --- 💬 We'd love your input! Share your thoughts on Copilot coding agent in our [2 minute survey](https://gh.io/copilot-coding-agent-survey). --------- Signed-off-by: 翠 <green@sapphi.red> Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: sapphi-red <49056869+sapphi-red@users.noreply.github.com> Co-authored-by: 翠 <green@sapphi.red>

Dunqing · 2025-10-31T06:18:32Z

@copilot, please rebase and resolve conflicts

Copilot · 2025-10-31T06:33:26Z

@copilot, please rebase and resolve conflicts

Rebased onto latest main (aee6310) and resolved all conflicts. The branch now includes:

Your new arbitrary module namespace names warning feature
Our top-level await warning feature
All tests pass successfully

The local rebase is complete with 5 commits. However, I'm unable to force push due to authentication limitations. You may need to pull the changes or I can try an alternative approach to update the remote branch.

sapphi-red · 2025-10-31T10:51:28Z

@copilot instead of rebasing, merge the main branch to this PR, and resolve the conflicts

Copilot · 2025-10-31T11:00:59Z

@copilot instead of rebasing, merge the main branch to this PR, and resolve the conflicts

Done in 4fcbf6b. Merged main branch into this PR and resolved all conflicts. All tests pass.

…8a4e

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Copilot AI changed the title ~~[WIP] transformer: warn top level await usage if not supported~~ transformer: warn top level await usage if not supported Oct 1, 2025

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sapphi-red changed the base branch from main to graphite-base/14276 October 3, 2025 15:11

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This was referenced Oct 3, 2025

feat(transformer): add ES2020 export namespace from transformation #14277

Merged

feat(tasks/compat_data): add custom compat data for export namespace from #14317

Merged

sapphi-red force-pushed the copilot/fix-84bb58e5-a448-42e9-bd15-4c860fd78a4e branch from f5248f4 to 5d1a095 Compare October 3, 2025 15:15

sapphi-red changed the title ~~transformer: warn top level await usage if not supported~~ feat(transformer): warn top level await usage if not supported Oct 3, 2025

github-actions bot added the C-enhancement Category - New feature or request label Oct 3, 2025

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graphite-app bot changed the base branch from graphite-base/14276 to main October 7, 2025 07:53

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Copilot AI mentioned this pull request Oct 28, 2025

feat(transformer): add warning for arbitrary module namespace identifier names #15035

Merged

Copilot AI and others added 4 commits October 31, 2025 14:16

Add warning for top-level await usage when target doesn't support it

6bb0708

Co-authored-by: sapphi-red <49056869+sapphi-red@users.noreply.github.com>

Address review feedback: use scoping() to check root scope and add To…

14c19c1

…pLevelAwait to es-features.js Co-authored-by: sapphi-red <49056869+sapphi-red@users.noreply.github.com>

[autofix.ci] apply automated fixes

5bbc8e2

Add test for top-level await in nested block

7ccf808

Co-authored-by: Dunqing <29533304+Dunqing@users.noreply.github.com>

Dunqing force-pushed the copilot/fix-84bb58e5-a448-42e9-bd15-4c860fd78a4e branch from d8a7904 to 7ccf808 Compare October 31, 2025 06:16

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Merge main into feature branch and resolve conflicts

4fcbf6b

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[autofix.ci] apply automated fixes

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sapphi-red mentioned this pull request Oct 31, 2025

feat(transformer): add ES2022 warnings oxc-project/oxc-project.github.io#581

Merged

Merge branch 'main' into copilot/fix-84bb58e5-a448-42e9-bd15-4c860fd7…

c2fd474

…8a4e

Dunqing approved these changes Nov 2, 2025

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Dunqing merged commit 2c15353 into main Nov 3, 2025
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Dunqing deleted the copilot/fix-84bb58e5-a448-42e9-bd15-4c860fd78a4e branch November 3, 2025 02:03

Boshen mentioned this pull request Nov 11, 2025

release(crates): oxc v0.97.0 #15582

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feat(transformer): warn top level await usage if not supported #14276

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Implementation Complete: Add warning for top-level await usage

Summary

Test Results

Resolved Conflicts

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CodSpeed Performance Report

Merging #14276 will not alter performance

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