feat(transformer): add ES2020 export namespace from transformation

[Copilot]

✅ Implementation Complete: ES2020 Export Namespace From Transformation

Successfully implemented the transformation for export * as ns from "mod" to convert it to:

import * as _ns from "mod";
export { _ns as ns };

Changes Made:

• Core transformation in es2020/export_namespace_from.rs
• ES2020 module integration and options
• Browser compatibility mapping in oxc_compat (auto-generated from custom compat data)
• Babel plugin support (transform-export-namespace-from)
• Target-based transformation (works with old browsers, skips modern ones)
• Code optimizations (removed clones, reserved capacity, used vec1)
• Custom compat data infrastructure for features not in compat-table
• Early return optimization to avoid unnecessary allocations
• Implemented GatherNodeParts for ModuleExportName to avoid string allocations
• All tests passing ✅

Code Review Addressed:

• Reserved capacity for statements vector
• Removed unnecessary clones via destructuring
• Used ctx.ast.vec1() for single-element vectors
• Created custom compat data system to avoid manual edits
• Imported TransformCtx directly
• Added early return when no export namespace declarations exist
• Implemented GatherNodeParts for ModuleExportName and use generate_uid_based_on_node

Example:

Input:

export * as ns from "mod";

Output:

import * as _ns from 'mod';
export { _ns as ns };

Original prompt

---

This section details on the original issue you should resolve

<issue_title>transformer: transform export * as ns from "mod"; to import * as ns from "mod"; export { ns }</issue_title>
<issue_description>This transformation is supported by babel: https://babeljs.io/docs/babel-plugin-transform-export-namespace-from

export * as ns from "mod";

// to

import * as _ns from "mod";
export { _ns as ns };
```</issue_description>

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

<comments>
</comments>

Fixes #14257

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[codspeed-hq]

CodSpeed Performance Report

Merging #14277 will not alter performance

_{Comparing copilot/fix-ced06a9a-b046-4d87-90de-6fe4af5bb650 (7b7c67b) with main (d0a8e3e)¹}

Summary

✅ 33 untouched
⏩ 4 skipped²

Footnotes

1. No successful run was found on main (a631dd7) during the generation of this report, so d0a8e3e was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

2. 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]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• feat(transformer): add ES2020 export namespace from transformation #14277 👈 (View in Graphite)
• feat(tasks/compat_data): add custom compat data for export namespace from #14317 : 1 other dependent PR (#14276 )
• main

---

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fixed

[Dunqing]

I just noticed that we should improve the case where there is no export * as ns from "mod".

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Additionally, we could try an alternative approach to implement this, which may have better performance than this in some scenarios.

How to implement it?

Do transform in exit_module_declaration. In this method, you can get a ModuleDeclaration, then check whether this is an ExportAllDeclaration whose exported is some, if so, you mutate it with the export part (export { _ns as ns }), and insert the import part (import * as _ns from "mod") by self.ctx.statement_injector.insert_before.

[Dunqing]

@copilot please check the requested changes