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
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