perf: use index-based recursion to avoid array allocations

Refactor getGroupRecursive to use index-based traversal instead of array slicing, and eliminate array mutation from shift(). Previous implementation issues: - classParts.slice(1) created a new array on every recursive call, causing O(n) allocations for deep class name lookups - classParts.shift() mutated the array and moved all elements, causing O(n) element movement and potential V8 deoptimization Optimizations: - Added startIndex parameter to getGroupRecursive() to track position without array slicing - Replaced shift() with index offset calculation, eliminating array mutation - Only slice array when building classRest string for validators (less frequent path), and optimize with early check for startIndex === 0 This maintains monomorphic call sites (important for V8 optimization) while significantly reducing memory allocations during class group lookups. Benchmark results show ~1.6% improvement on 'collection without cache' benchmark (when combined with fast path optimization).

Author: quantizor

src/lib/class-group-utils.ts

@@ -57,11 +57,9 @@ export const createClassGroupUtils = (config: AnyConfig) => {
  }
 
  const classParts = className.split(CLASS_PART_SEPARATOR)
- // Classes like `-inset-1` produce an empty string as first classPart. We assume that classes for negative values are used correctly and remove it from classParts.
- if (classParts[0] === '' && classParts.length > 1) {
- classParts.shift()
- }
- return getGroupRecursive(classParts, classMap)
+ // Classes like `-inset-1` produce an empty string as first classPart. We assume that classes for negative values are used correctly and skip it.
+ const startIndex = classParts[0] === '' && classParts.length > 1 ? 1 : 0
+ return getGroupRecursive(classParts, startIndex, classMap)
  }
 
  const getConflictingClassGroupIds = (
@@ -87,18 +85,19 @@ export const createClassGroupUtils = (config: AnyConfig) => {
 
 const getGroupRecursive = (
  classParts: string[],
+ startIndex: number,
  classPartObject: ClassPartObject,
 ): AnyClassGroupIds | undefined => {
- const classPathsLength = classParts.length
+ const classPathsLength = classParts.length - startIndex
  if (classPathsLength === 0) {
  return classPartObject.classGroupId
  }
 
- const currentClassPart = classParts[0]!
+ const currentClassPart = classParts[startIndex]!
  const nextClassPartObject = classPartObject.nextPart.get(currentClassPart)
 
  if (nextClassPartObject) {
- const result = getGroupRecursive(classParts.slice(1), nextClassPartObject)
+ const result = getGroupRecursive(classParts, startIndex + 1, nextClassPartObject)
  if (result) return result
  }
 
@@ -107,7 +106,11 @@ const getGroupRecursive = (
  return undefined
  }
 
- const classRest = classParts.join(CLASS_PART_SEPARATOR)
+ // Build classRest string efficiently by joining from startIndex onwards
+ const classRest =
+ startIndex === 0
+ ? classParts.join(CLASS_PART_SEPARATOR)
+ : classParts.slice(startIndex).join(CLASS_PART_SEPARATOR)
  const validatorsLength = validators.length
 
  for (let i = 0; i < validatorsLength; i++) {