Summary

Reduces CSS selector pruning overhead by eliminating unnecessary allocations and redundant work in the hot path.

Changes:

• Replace .slice() + .shift()/.pop() in apply_selector with index-based from/to params — avoids O(n) array copies per recursive call
• Merge has_selectors/other_selectors split in relative_selector_might_apply_to_node into a single pass — eliminates 2 temporary array allocations per call
• Hoist name.toLowerCase() out of the inner loop in attribute_matches
• Replace value.split(/\s/).includes() with indexOf + boundary checks in test_attribute for ~= — avoids array allocation on every class match
• Skip name.replace() regex when selector name has no backslash

Benchmark

Interleaved benchmark (5 rounds, alternating baseline/optimized):

--- Round 1 ---
  Baseline:  min=59.58ms  median=64.63ms
  Optimized: min=47.20ms  median=54.35ms
--- Round 2 ---
  Baseline:  min=59.11ms  median=64.90ms
  Optimized: min=48.36ms  median=54.74ms
--- Round 3 ---
  Baseline:  min=58.38ms  median=64.06ms
  Optimized: min=48.38ms  median=53.83ms
--- Round 4 ---
  Baseline:  min=58.49ms  median=63.99ms
  Optimized: min=48.45ms  median=53.82ms
--- Round 5 ---
  Baseline:  min=58.40ms  median=64.07ms
  Optimized: min=48.97ms  median=54.64ms

Best min:    Before=58.38ms  After=47.20ms  Improvement=19.1%
Best median: Before=63.99ms  After=53.82ms  Improvement=15.9%

CPU profile before → after:

Test plan

• All 196 CSS tests pass (180 samples + 16 parse)
• All 31 snapshot tests pass
• All 2380 runtime-runes tests pass
• All 3291 runtime-legacy tests pass
• All 145 compiler-errors tests pass
• All 326 validator tests pass
• Added css-prune-edge-cases test covering: ~= word matching (substring vs whole word), deep combinator chains (4+ levels), :has() combined with class selectors, escaped selectors, :is()/:where()/:not() with combinators
• Edge case test passes on both baseline and optimized code

🤖 Generated with Claude Code