Credence.Syntax.PreferCondDoKeyword (credence v0.8.0)

Repairs cond -> written in place of cond do.

LLMs occasionally emit cond -> — mixing Rust/OCaml match-arm syntax into Elixir — where Elixir requires cond do. The bare cond -> never parses, so this is a REPAIR: replace the offending cond -> with cond do, opening the block the trailing end was already waiting to close. cond do … end is the only valid form, so the rewrite is behaviour-neutral.

Detection is driven by the parser itself. The rule replaces a single cond -> occurrence and commits the result only when Code.string_to_quoted/1 then succeeds. A cond -> sitting inside a string, heredoc, or comment is invisible to the parser, so replacing it never resolves a parse error and is never the committed occurrence — it is left untouched even when the file is unparseable for an unrelated reason.

Bad (won't parse)

cond ->
  list == [] -> nil
  true -> Enum.min(list)
end

Good

cond do
  list == [] -> nil
  true -> Enum.min(list)
end