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

Copilot · 2025-10-28T12:01:39Z

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

// 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.

Original prompt

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.

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graphite-app · 2025-10-28T12:01:46Z

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- Added ArbitraryModuleNamespaceNames to custom-compat-data.js with browser support info - Regenerated es_features.rs with the new ES2020ArbitraryModuleNamespaceNames feature - Added arbitrary_module_namespace_names option to ES2020Options - Implemented warning logic in ES2020 transformer for string literal module export names - Added delegation in main transformer for import/export specifiers - Added tests to verify warnings are emitted correctly - Updated snapshot tests Co-authored-by: sapphi-red <49056869+sapphi-red@users.noreply.github.com>

- Test that Chrome 90 (which supports the feature) does not emit warnings - Test that multiple string literals emit multiple warnings - Test that normal identifiers do not trigger warnings - All tests passing Co-authored-by: sapphi-red <49056869+sapphi-red@users.noreply.github.com>

tasks/compat_data/package-lock.json

tasks/compat_data/custom-compat-data.js

crates/oxc_transformer/tests/integrations/es_target.rs

- Remove tasks/compat_data/package-lock.json as requested - Fix browser compatibility versions to correct values (Chrome 88, Opera 74, Edge 88, Deno 1.6, Opera Mobile 63) - Change test case from chrome89 to es2019 for consistency - Update all test cases to use chrome87 (unsupported version) - Regenerate es_features.rs with corrected compatibility data - All tests passing Co-authored-by: sapphi-red <49056869+sapphi-red@users.noreply.github.com>

crates/oxc_transformer/src/es2020/mod.rs

crates/oxc_transformer/tests/integrations/es_target.rs

Signed-off-by: 翠 <green@sapphi.red>

crates/oxc_transformer/tests/integrations/es_target.rs

Signed-off-by: 翠 <green@sapphi.red>

sapphi-red · 2025-10-28T15:57:52Z

@copilot fix the lint error

codspeed-hq · 2025-10-28T15:58:26Z

CodSpeed Performance Report

Merging #15035 will not alter performance

_{Comparing copilot/add-warning-for-arbitrary-namespace (57048f7) with main (1611b4f)}

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. ↩

Fixed clippy::collapsible_if warnings by combining nested if statements with let patterns using && operator in: - enter_import_specifier - enter_export_all_declaration Co-authored-by: sapphi-red <49056869+sapphi-red@users.noreply.github.com>

Copilot · 2025-10-28T16:04:41Z

@copilot fix the lint error

Fixed in 57048f7. Collapsed nested if statements using && with let patterns to resolve clippy::collapsible_if warnings.

Copilot

Pull Request Overview

This PR implements warnings for the ES2020 "Arbitrary module namespace identifier names" feature, which allows string literals as import/export specifiers (e.g., export { foo as "kebab-case" }). When targeting environments that don't support this feature, the transformer will emit warnings.

Key Changes:

Added browser/runtime compatibility data for the feature (Chrome 88+, Firefox 87+, Safari 14.1+, etc.)
Implemented warning logic in the ES2020 transformer for string literal specifiers in import/export statements
Added configuration option and environment target mapping

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tasks/compat_data/data.json	Added compatibility data entry for ArbitraryModuleNamespaceNames with browser/runtime versions
tasks/compat_data/custom-compat-data.js	Added custom compatibility data definition with TC39 proposal reference
crates/oxc_transformer/tests/integrations/snapshots/es_target.snap	Added snapshot test showing warning output for ES2019 target
crates/oxc_transformer/tests/integrations/es_target.rs	Added integration test case for arbitrary module namespace names
crates/oxc_transformer/src/options/mod.rs	Added arbitrary_module_namespace_names option mapping from Babel options
crates/oxc_transformer/src/options/env.rs	Added environment target configuration for the feature
crates/oxc_transformer/src/lib.rs	Added traverse hooks for import/export specifiers and export all declarations
crates/oxc_transformer/src/es2020/options.rs	Added arbitrary_module_namespace_names boolean option to ES2020Options
crates/oxc_transformer/src/es2020/mod.rs	Implemented warning logic for string literal specifiers in import/export nodes
crates/oxc_compat/src/es_features.rs	Added ES2020ArbitraryModuleNamespaceNames feature enum and compatibility targets

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crates/oxc_transformer/src/es2020/mod.rs

Initial plan

95d471c

Copilot AI assigned Copilot and sapphi-red Oct 28, 2025

Copilot started work on behalf of sapphi-red October 28, 2025 12:02 View session

Copilot AI and others added 3 commits October 28, 2025 12:31

Remove temporary test file

409c32f

Copilot AI changed the title ~~[WIP] Add warning for arbitrary module namespace identifier names~~ feat(transformer): Add warning for arbitrary module namespace identifier names Oct 28, 2025

Copilot AI requested a review from sapphi-red October 28, 2025 12:37

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Copilot started work on behalf of sapphi-red October 28, 2025 14:12 View session

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chore: tweak

1445efd

Signed-off-by: 翠 <green@sapphi.red>

github-actions bot added A-transformer Area - Transformer / Transpiler C-enhancement Category - New feature or request labels Oct 28, 2025

sapphi-red reviewed Oct 28, 2025

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chore: tweak

af55e78

Signed-off-by: 翠 <green@sapphi.red>

sapphi-red changed the title ~~feat(transformer): Add warning for arbitrary module namespace identifier names~~ feat(transformer): add warning for arbitrary module namespace identifier names Oct 28, 2025

Copilot started work on behalf of sapphi-red October 28, 2025 15:58 View session

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sapphi-red approved these changes Oct 28, 2025

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sapphi-red marked this pull request as ready for review October 28, 2025 16:12

sapphi-red requested review from Dunqing and overlookmotel as code owners October 28, 2025 16:12

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Dunqing approved these changes Oct 31, 2025

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Dunqing merged commit aee6310 into main Oct 31, 2025
45 of 47 checks passed

Dunqing deleted the copilot/add-warning-for-arbitrary-namespace branch October 31, 2025 06:17

sapphi-red mentioned this pull request Oct 31, 2025

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

Merged

Boshen mentioned this pull request Nov 11, 2025

release(crates): oxc v0.97.0 #15582

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

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Merging #15035 will not alter performance

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