DerivClause list is not populated for (TyConI (DataD ...))
% cat Test.hs
{-# LANGUAGE LambdaCase #-}
module Test where
import Language.Haskell.TH
test :: Name -> Q [Dec]
test name = reify name >>= \case
TyConI dec -> do
runIO $ print dec
pure []
_ -> pure []
% cat Run.hs
{-# LANGUAGE TemplateHaskell #-}
import Test
data Foo = Foo deriving (Eq, Ord, Show)
test ''Foo
% ghc Run.hs
[2 of 2] Compiling Main ( Run.hs, Run.o )
DataD [] Main.Foo [] Nothing [NormalC Main.Foo []] []One might expect the DataD to mention Eq, Ord, Show in the DerivClause list, but it doesn't.
This behavior manifests with every ghc version I tried: 8.0.2, 8.2.2, 8.4.2. I also asked a question whether it's intended behaviour on #haskell, and I've been advised to open a bug report, so here it is.
Trac metadata
| Trac field | Value |
|---|---|
| Version | 8.4.2 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Template Haskell |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |