Credence.Rule.NoIsPrefix (credence v0.2.0)

Style rule: Detects functions named with an is_ prefix that are not guard-safe BIFs.

In Elixir, predicate functions use a trailing ? by convention (e.g. valid?/1, palindrome?/1). The is_ prefix is reserved for guard-safe type checks from Erlang (is_list/1, is_integer/1, etc.). User-defined functions named is_foo look like guards but aren't usable in guards, which misleads readers.

Bad

def is_valid_palindrome(s), do: ...
defp is_empty(list), do: ...

Good

def valid_palindrome?(s), do: ...
defp empty?(list), do: ...