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This program

{-# LANGUAGE LinearTypes, EmptyCase #-}
module M where

{-# NOINLINE f #-}
f :: a %1-> ()
f x = case () of {}

fails Linear Lint with -dlinear-core-lint -O. There are three problems.

1. castBottomExpr converts (case x :: T of {}) :: T to x. Commenting this line:

--- a/compiler/GHC/Core/Make.hs
+++ b/compiler/GHC/Core/Make.hs
@@ -239,7 +239,7 @@ castBottomExpr :: CoreExpr -> Type -> CoreExpr
 -- return an expression of type 'ty'
 -- See Note [Empty case alternatives] in GHC.Core
 castBottomExpr e res_ty
-  | e_ty `eqType` res_ty = e
+  -- | e_ty `eqType` res_ty = e
   | otherwise            = Case e (mkWildValBinder One e_ty) res_ty []
   where
     e_ty = exprType e

works around the problem, but the correct fix is to do this transformation only if the usage environment of the case is completely unrestricted. This needs #18768.

2. Worker/wrapper moves the empty case to a separate binding:

f = \ (@a_sCY) (w_sCZ [Dmd=B] :: a_sCY) -> $wf_sD1 @a_sCY void#

where $wf_sD1 contains the empty case. This fails Lint, can be worked around with -fno-worker-wrapper.

3. CorePrep eliminates empty case, just like point 1.

-- Eliminate empty case
-- See Note [Unsafe coercions]
cpeRhsE env (Case scrut _ ty [])
  = ...

This ticket is blocked on #18768.