diff options
Diffstat (limited to 'compiler/GHC')
| -rw-r--r-- | compiler/GHC/HsToCore/Quote.hs | 8 |
1 files changed, 5 insertions, 3 deletions
diff --git a/compiler/GHC/HsToCore/Quote.hs b/compiler/GHC/HsToCore/Quote.hs index 07ab2959ba..292cb4dca0 100644 --- a/compiler/GHC/HsToCore/Quote.hs +++ b/compiler/GHC/HsToCore/Quote.hs @@ -2122,10 +2122,12 @@ wrapGenSyms binds body@(MkC b) = do { var_ty <- lookupType nameTyConName ; go var_ty binds } where - (_, [elt_ty]) = tcSplitAppTys (exprType b) + (_, elt_ty) = tcSplitAppTy (exprType b) -- b :: m a, so we can get the type 'a' by looking at the - -- argument type. NB: this relies on Q being a data/newtype, - -- not a type synonym + -- argument type. Need to use `tcSplitAppTy` here as since + -- the overloaded quotations patch the type of the expression can + -- be something more complicated than just `Q a`. + -- See #17839 for when this went wrong with the type `WriterT () m a` go _ [] = return body go var_ty ((name,id) : binds) |