feat(minifier): remove unused assignments for vars

[sapphi-red]

I found that the temporary variable are kept. This change would remove them.
Variables that were declared with var did not have SymbolValue populated and that caused those variables to bail out at this line.

oxc/crates/oxc_minifier/src/peephole/remove_unused_expression.rs

Lines 624 to 626 in 2141c18

	let Some(symbol_value) = ctx.state.symbol_values.get_symbol_value(symbol_id) else {
	return false;
	};

I think TDZ needs to be considered when inlining the values, but does not affect removing the unused assignments.

[sapphi-red]

• feat(minifier): support remaining expressions for single use variable inlining #13280
• feat(ecmascript): implement MayHaveSideEffects for AssignmentTarget #13279
• feat(minifier): support more statements for single use variable inlining #13277
• feat(minifier): support more expressions for single use variable inlining #13276
• feat(minifier): implement basic single use variable inlining #13275
• feat(minifier): remove unnecessary parenthesis from nested optional chaining #13268
• feat(minifier): remove unused assignments for vars #13231 👈 (View in Graphite)
• fix(minifier): keep variables that are modified by combined assignments made by minification #13267
• fix(minifier): keep property access before call expressions as-is to preserve this value #13278
• main

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[Copilot]

Pull Request Overview

This PR implements support for removing unused assignments for var declarations in the minifier. Previously, variables declared with var did not have SymbolValue populated, causing them to bail out during unused assignment removal optimization.

• Modified the inline module to populate SymbolValue for var declarations while avoiding constant value inlining
• Updated test cases to verify that unused var assignments are now properly removed
• Achieved improved minification results across multiple test files

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
crates/oxc_minifier/src/peephole/inline.rs	Modified init_symbol_value to populate symbol values for var declarations while skipping constant value inlining
crates/oxc_minifier/src/peephole/remove_unused_expression.rs	Updated test cases to verify unused var assignment removal works correctly
tasks/minsize/minsize.snap	Updated snapshot showing improved minification sizes across test files

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[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #13231 will degrade performances by 5.55%

_{Comparing 08-20-feat_minifier_collect_symbol_information_for_vars (8ca9909) with main (e7a49ed)¹}

Summary

❌ 1 regressions
✅ 33 untouched benchmarks

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

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
❌	minifier[react.development.js]	2.1 ms	2.3 ms	-5.55%

Footnotes

1. No successful run was found on main (0e804aa) during the generation of this report, so e7a49ed was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[graphite-app]

Merge activity

• Aug 24, 8:30 AM UTC: Boshen added this pull request to the Graphite merge queue.
• Aug 24, 8:50 AM UTC: Merged by the Graphite merge queue.