Introduce and use DerivClauseTys (#18662)

This switches `deriv_clause_tys` so that instead of using a list of
`LHsSigType`s to represent the types in a `deriving` clause, it now
uses a sum type. `DctSingle` represents a `deriving` clause with no
enclosing parentheses, while `DctMulti` represents a clause with
enclosing parentheses. This makes pretty-printing easier and avoids
confusion between `HsParTy` and the enclosing parentheses in
`deriving` clauses, which are different semantically.

Fixes #18662.

1 files changed, 7 insertions, 3 deletions

diff --git a/compiler/GHC/Iface/Ext/Ast.hs b/compiler/GHC/Iface/Ext/Ast.hs
index 52a62862ce..b123450b60 100644
--- a/compiler/GHC/Iface/Ext/Ast.hs
+++ b/compiler/GHC/Iface/Ext/Ast.hs
@@ -1507,12 +1507,16 @@ instance ToHie (Located [Located (HsDerivingClause GhcRn)]) where
 
 instance ToHie (Located (HsDerivingClause GhcRn)) where
   toHie (L span cl) = concatM $ makeNode cl span : case cl of
-      HsDerivingClause _ strat (L ispan tys) ->
+      HsDerivingClause _ strat dct ->
         [ toHie strat
-        , locOnly ispan
-        , toHie $ map (TS (ResolvedScopes [])) tys
+        , toHie dct
         ]
 
+instance ToHie (Located (DerivClauseTys GhcRn)) where
+  toHie (L span dct) = concatM $ makeNode dct span : case dct of
+      DctSingle _ ty -> [ toHie $ TS (ResolvedScopes[]) ty ]
+      DctMulti _ tys -> [ toHie $ map (TS (ResolvedScopes [])) tys ]
+
 instance ToHie (Located (DerivStrategy GhcRn)) where
   toHie (L span strat) = concatM $ makeNode strat span : case strat of
       StockStrategy -> []