MikaCredoRules.NoBlanketRescue (MikaCredoRules v0.1.0)

A rescue clause must not catch every exception only to swallow it.

A blanket rescue _ -> or rescue error -> that neither reraises, raises, nor logs converts every crash — typos, match errors, genuine bugs — into a silent wrong value. Rescue the specific exceptions you can handle, and let everything else crash.

# BAD — swallows every exception, bugs included
def read_file(path) do
  File.read!(path)
rescue
  _ -> :error
end

# GOOD — rescues only the exception it can handle
def read_file(path) do
  File.read!(path)
rescue
  error in File.Error -> {:error, error}
end

A blanket rescue is allowed when its body handles the exception it caught — reraising, raising a wrapping exception, or logging it:

# GOOD — logs before returning an error value
def read_file(path) do
  File.read!(path)
rescue
  error ->
    Logger.error("#{__MODULE__}: read failed, error: #{inspect(error)}")
    {:error, error}
end

Both the explicit try do ... rescue block and the implicit def ... rescue form are checked.

What counts as handling is configurable through :allowed_recovery_calls. Calls are matched by name, so a Logger renamed through an alias is not recognised.