feat(ecmascript): handle typeof guarded global access as side effect free

[Copilot]

This PR integrates sophisticated side effect analysis for unbound identifier references directly into Oxc's MayHaveSideEffects trait implementations, rather than exposing it as a separate public function.

What this implements

The enhanced analysis recognizes guard patterns that make accessing potentially undefined global variables safe:

// Safe to access `x` in the right side since we know it's defined  
typeof x !== 'undefined' && x

// Safe to access `x` in the else branch since we know it's defined
typeof x === 'undefined' ? fallback : x

// Safe to access `x` in the right side (string comparison optimization)
typeof x < 'u' && x

Implementation approach

Following code review feedback, the logic is integrated directly into the trait implementations:

• LogicalExpression: Enhanced to analyze AND/OR patterns with typeof guards
• ConditionalExpression: Enhanced to analyze ternary patterns with typeof guards
• Private helper function: Contains the core analysis logic, not exposed in the public API

Testing

Comprehensive tests have been added to crates/oxc_minifier/tests/ecmascript/may_have_side_effects.rs covering:

• Logical AND patterns: typeof x !== 'undefined' && x
• Logical OR patterns: typeof x === 'undefined' || x
• Conditional patterns: typeof x === 'undefined' ? fallback : x
• String comparison optimizations: typeof x < 'u' && x
• Negative cases ensuring side effects are properly detected when guards don't apply

Use cases

This enhancement is particularly valuable for:

• Tree-shaking optimizations - determining when global variable access can be safely eliminated
• Dead code elimination - identifying unreachable code paths based on type guards
• Bundler optimizations - similar to how Rolldown and esbuild analyze side effects

The implementation maintains full compatibility with Oxc's existing side effects analysis framework while providing enhanced capabilities for modern JavaScript bundling and optimization tools.

Ported from: https://github.com/evanw/esbuild/blob/d34e79e2a998c21bb71d57b92b0017ca11756912/internal/js_ast/js_ast_helpers.go#L2594-L2639

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[graphite-app]

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[sapphi-red]

@copilot add tests to https://github.com/oxc-project/oxc/blob/main/crates/oxc_minifier/tests/ecmascript/may_have_side_effects.rs

[Copilot]

@copilot add tests to https://github.com/oxc-project/oxc/blob/main/crates/oxc_minifier/tests/ecmascript/may_have_side_effects.rs

Added comprehensive tests for the typeof guard patterns in may_have_side_effects.rs. The tests cover all the enhanced side effect analysis patterns including logical AND/OR patterns, conditional expressions, and negative cases to ensure the optimization works correctly. Tests committed in 3b385d6.

[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #12981 will not alter performance

_{Comparing copilot/fix-f1053a7e-2cd4-45ea-b4e3-78f8bb81fcb0 (a9e817c) with main (ca91a26)}

Summary

✅ 34 untouched benchmarks

[sapphi-red]

• feat(ecmascript): handle typeof guarded global access as side effect free #12981 👈 (View in Graphite)
• main

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[Copilot]

Pull Request Overview

This PR enhances Oxc's side effect analysis to recognize typeof guard patterns that make accessing potentially undefined global variables safe. The implementation integrates sophisticated guard pattern detection directly into the MayHaveSideEffects trait implementations.

Key changes:

• Enhanced LogicalExpression and ConditionalExpression to analyze typeof guard patterns
• Added comprehensive helper function for detecting safe unbound identifier access patterns
• Extensive test coverage for various guard patterns including equality checks and string comparisons

Reviewed Changes

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

File	Description
crates/oxc_ecmascript/src/side_effects/may_have_side_effects.rs	Implements core guard pattern analysis logic in trait implementations and adds helper function
crates/oxc_minifier/tests/ecmascript/may_have_side_effects.rs	Adds comprehensive test cases covering all supported guard patterns and edge cases