Feat/deep merge config optimizations

[tyrauber]

Security Hardening and Performance Optimization for Style Filtering

Summary

This PR hardens the CSS variable filtering implementation with critical security fixes and performance optimizations based on red team review.

Changes

Commit 1: 3f1d395 - Refactor: harden style filtering with security and performance fixes

Critical fixes:

• Add null safety checks to prevent crashes
• Use hasOwnProperty to prevent prototype pollution attacks
• Add depth limit (100) to prevent stack overflow on deep nesting
• Fix falsy value filtering (preserve 0, false, empty strings)
• Use Object.keys() to properly filter Symbol properties
• Replace spread operator with reduce() for large array performance

Performance improvements:

• Extract hasNonOverlappingProperties() helper (DRY)
• Single-pass array filtering in filterCssVariables()
• Early exit in flattenStyleArray()
• Handle arrays with 10k+ items without stack overflow

Security hardening:

• Prevent prototype pollution via for...in loops
• Filter inherited properties with hasOwnProperty checks
• Remove Symbol properties for React Native compatibility

Commit 2: dffa268 - Test: add comprehensive edge case tests for security hardening

Red team validation tests covering:

• Circular references with depth limit protection
• Sparse arrays with undefined holes
• Objects with only Symbol properties (RN filtering)
• Mixed null/undefined/falsy values preservation
• Frozen/sealed objects handling
• Very deep nesting (105 levels) beyond limit
• Prototype pollution prevention (proto)
• Arrays with custom properties
• Empty arrays and objects
• Numeric string keys

All 10 edge case tests pass, validating:

• No crashes on malformed input
• Prototype pollution prevention
• Circular reference handling
• Stack overflow prevention
• Symbol filtering for React Native compatibility
• Null safety across all code paths

Test Results

✅ 970 passing tests (42 rightIsInline-specific)
✅ 0 TypeScript errors
✅ 0 linting warnings

Files Changed

• src/native/styles/index.ts: +66, -48
• src/__tests__/native/rightIsInline.test.tsx: +175

Total: 2 files changed, +241 insertions(+), -48 deletions(-)

[Copilot]

Pull Request Overview

This PR refactors the CSS variable filtering logic in the native styles module to improve code maintainability and add comprehensive test coverage. The changes centralize the filtering logic, add proper null/undefined handling, and introduce style flattening optimizations.

• Extracts CSS variable filtering into reusable utility functions (filterCssVariables, hasNonOverlappingProperties, flattenStyleArray)
• Enhances handling of inline styles with improved null safety and edge case coverage
• Adds extensive test suite covering CSS variable stripping, important style interactions, and edge cases

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
src/native/styles/index.ts	Adds three new utility functions for style processing and refactors deepMergeConfig to use centralized filtering logic with better null handling
src/tests/native/rightIsInline.test.tsx	New comprehensive test file covering CSS variable filtering, inline style handling, and edge cases including circular references and prototype pollution
src/tests/native/className-with-style.test.tsx	Adds tests for important style overrides and multiple className properties with inline styles

[danstepanov]

Seems like overkill but I'm with it