Enable maxBound checks for OverloadedLists (Fixes #18172)

Consider the Literal `[256] :: [Data.Word.Word8]`

When the `OverloadedLists` extension is not active, then the `ol_ext` field
in the `OverLitTc` record that is passed to the function `getIntegralLit`
contains the type `Word8`. This is a simple type, and we can use its
type constructor immediately for the `warnAboutOverflowedLiterals` function.

When the `OverloadedLists` extension is active, then the `ol_ext` field
contains the type family `Item [Word8]`. The function `nomaliseType` is used
to convert it to the needed type `Word8`.

1 files changed, 6 insertions, 4 deletions

diff --git a/compiler/GHC/HsToCore/Expr.hs b/compiler/GHC/HsToCore/Expr.hs
index ff23a9c168..6b55926af3 100644
--- a/compiler/GHC/HsToCore/Expr.hs
+++ b/compiler/GHC/HsToCore/Expr.hs
@@ -945,8 +945,9 @@ dsArithSeq :: PostTcExpr -> (ArithSeqInfo GhcTc) -> DsM CoreExpr
 dsArithSeq expr (From from)
   = App <$> dsExpr expr <*> dsLExprNoLP from
 dsArithSeq expr (FromTo from to)
-  = do dflags <- getDynFlags
-       warnAboutEmptyEnumerations dflags from Nothing to
+  = do fam_envs <- dsGetFamInstEnvs
+       dflags <- getDynFlags
+       warnAboutEmptyEnumerations fam_envs dflags from Nothing to
        expr' <- dsExpr expr
        from' <- dsLExprNoLP from
        to'   <- dsLExprNoLP to
@@ -954,8 +955,9 @@ dsArithSeq expr (FromTo from to)
 dsArithSeq expr (FromThen from thn)
   = mkApps <$> dsExpr expr <*> mapM dsLExprNoLP [from, thn]
 dsArithSeq expr (FromThenTo from thn to)
-  = do dflags <- getDynFlags
-       warnAboutEmptyEnumerations dflags from (Just thn) to
+  = do fam_envs <- dsGetFamInstEnvs
+       dflags <- getDynFlags
+       warnAboutEmptyEnumerations fam_envs dflags from (Just thn) to
        expr' <- dsExpr expr
        from' <- dsLExprNoLP from
        thn'  <- dsLExprNoLP thn