Credence.Rule.NoStringLengthForCharCheck (credence v0.3.2)

Performance rule: Detects String.length(x) == 1 (or != 1) used to validate that a string is a single character. String.length/1 traverses the entire string to count grapheme clusters, making it O(n). For a simple single-character check, pattern matching on the result of String.graphemes/1 is more expressive and idiomatic. This rule automatically rewrites the comparison to use match?/2 with String.graphemes/1, which produces a clean boolean result that works in any expression context.

Bad

if String.length(target_char) != 1 do
  raise ArgumentError, "expected a single character"
end
String.length(s) == 1
1 === String.length(s)

Good

if not match?([_], String.graphemes(target_char)) do
  raise ArgumentError, "expected a single character"
end
match?([_], String.graphemes(s))