Credence.Pattern.NoCaseTrueFalse (credence v0.6.0)

Detects case expr do true -> …; false -> … end that should be if/else.

LLMs frequently transliterate Python's if/else through a case on a boolean expression with explicit true/false (or _) clauses. Idiomatic Elixir uses if/else when the condition is already a boolean.

Only flags cases where the subject is a boolean expression (comparison, function call, operator) — not a plain variable, which may be a legitimate pattern match on a tristate value.

Detected patterns

case expr do true -> A; false -> B end
case expr do false -> B; true -> A end
case expr do true -> A; _ -> B end
case expr do false -> B; _ -> A end

Bad

case rem(n, 2) == 0 do
  true -> :even
  false -> :odd
end

Good

if rem(n, 2) == 0 do
  :even
else
  :odd
end

Auto-fix

Rewrites the case to if/else, placing the true body (or the wildcard counterpart) in the do block and the false body in else.