fix(minifier): don't inline single use variables that are not literals to for statement initializers

[sapphi-red]

function wrapper() { var x = a; for (let a of x) console.log(a) }

should not be compress to

function wrapper() { for (let a of a) console.log(a) }

because a points to a different variable as the scope is different.
This PR fixes those kinds of cases for all for statements.

Found in rolldown/rolldown#6220

refs #13755

[sapphi-red]

• test(minifier): merge variable declarations into for statement initializers #13770
• fix(minifier): don't inline single use variables that are not literals to for statement initializers #13769 👈 (View in Graphite)
• main

---

How to use the Graphite Merge Queue

Add either label to this PR to merge it via the merge queue:

• 0-merge - adds this PR to the back of the merge queue
• hotfix - for urgent hot fixes, skip the queue and merge this PR next

You must have a Graphite account in order to use the merge queue. Sign up using this link.

An organization admin has enabled the Graphite Merge Queue in this repository.

Please do not merge from GitHub as this will restart CI on PRs being processed by the merge queue.

This stack of pull requests is managed by Graphite. Learn more about stacking.

[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #13769 will not alter performance

_{Comparing 09-15-fix_minifier_don_t_inline_single_use_variables_that_are_not_literals_to_for_statement_initializers (f0af9a4) with main (b6eba27)¹}

Summary

✅ 37 untouched

Footnotes

1. No successful run was found on main (f0af9a4) during the generation of this report, so b6eba27 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[Copilot]

Pull Request Overview

This PR fixes a bug in the minifier's single-use variable inlining optimization where variables were incorrectly inlined into for statement initializers when they would reference different scoped variables with the same name.

• Prevents inlining non-literal variables into for statement binding declarations to avoid scope confusion
• Updates test cases to cover the specific edge cases involving variable scope conflicts
• Adds parameter to control when only literal values should be inlined

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
crates/oxc_minifier/src/peephole/minimize_statements.rs	Adds scope-aware parameter to prevent non-literal inlining in for statements
crates/oxc_minifier/tests/peephole/inline_single_use_variable.rs	Updates and adds test cases to verify correct behavior with scoped variables
tasks/track_memory_allocations/allocs_minifier.snap	Updated memory allocation snapshots
tasks/minsize/minsize.snap	Updated minification size snapshots

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[Boshen]

Merge activity

• Sep 15, 5:59 AM UTC: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
• Sep 15, 5:59 AM UTC: Boshen added this pull request to the Graphite merge queue.
• Sep 15, 6:05 AM UTC: Merged by the Graphite merge queue.