The following program:

{-# LANGUAGE LambdaCase #-}

foo =
    if True
    then
        \case ->
            1 -> 2
    else id

Produces this message:

problem.hs:4:5:
    parse error in if statement: missing required else clause

The problem in the code is that there's a -> after the \case.

I don't know if a better error message can be generated, but this one is really unhelpful.