feat(minifier): inline single use variables within the same variable declarations

[sapphi-red]

Compress

var a = foo, b = a;

into

var b = foo;

refs #13912

[sapphi-red]

• feat(minifier): inline single use variables within the same variable declarations #13959 👈 (View in Graphite)
• main

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[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #13959 will degrade performances by 3.59%

_{Comparing 09-20-feat_minifier_inline_single_use_variables_within_the_same_variable_declarations (402e6c7) with main (7e42b0a)}

Summary

❌ 1 regression
✅ 32 untouched
⏩ 4 skipped¹

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
❌	minifier[cal.com.tsx]	31.5 ms	32.7 ms	-3.59%

Footnotes

1. 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. ↩

[Copilot]

Pull Request Overview

Adds a peephole optimization to inline single-use variables within the same variable declaration list (e.g., var a = foo, b = a; -> var b = foo;), and refactors internal logic to support reuse across contexts.

• Implement inline-within-declaration optimization and invoke it for standalone var/let/const declarations and for-loop init declarations
• Extract shared logic for substituting single-use symbols from a list of declarators
• Update tests and snapshots to reflect improved minification and allocation/sizing deltas

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tasks/track_memory_allocations/allocs_minifier.snap	Updates memory allocation snapshots reflecting new optimization effects.
tasks/minsize/minsize.snap	Updates size metrics snapshots showing slightly improved minification.
crates/oxc_minifier/tests/peephole/inline_single_use_variable.rs	Adds tests covering inlining within the same variable declarations, including for-loop init and using/let cases.
crates/oxc_minifier/src/peephole/minimize_statements.rs	Implements the inlining within declaration lists, refactors substitution logic into a reusable helper, and wires calls at appropriate transformation points.
crates/oxc_minifier/src/peephole/minimize_conditions.rs	Adjusts a test to expect additional constant folding/elimination due to the new optimization.

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[Boshen]

Merge activity

• Sep 27, 6:37 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 27, 6:47 AM UTC: This pull request can not be added to the Graphite merge queue. Please try rebasing and resubmitting to merge when ready.
• Sep 27, 6:47 AM UTC: Graphite disabled "merge when ready" on this PR due to: a merge conflict with the target branch; resolve the conflict and try again..
• Sep 27, 6:48 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 27, 6:48 AM UTC: This pull request can not be added to the Graphite merge queue. Please try rebasing and resubmitting to merge when ready.
• Sep 27, 6:48 AM UTC: Graphite disabled "merge when ready" on this PR due to: a merge conflict with the target branch; resolve the conflict and try again..
• Sep 27, 6:48 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 27, 6:49 AM UTC: This pull request can not be added to the Graphite merge queue. Please try rebasing and resubmitting to merge when ready.
• Sep 27, 6:49 AM UTC: Graphite disabled "merge when ready" on this PR due to: a merge conflict with the target branch; resolve the conflict and try again..
• Sep 27, 6:49 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 27, 7:24 AM UTC: This pull request can not be added to the Graphite merge queue. Please try rebasing and resubmitting to merge when ready.
• Sep 27, 7:24 AM UTC: Graphite disabled "merge when ready" on this PR due to: a merge conflict with the target branch; resolve the conflict and try again..
• Sep 27, 7:24 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 27, 8:47 AM UTC: Boshen added this pull request to the Graphite merge queue.
• Sep 27, 8:53 AM UTC: Merged by the Graphite merge queue.