‘Identity instance’: Outputable SDoc

Is there reason why there isn't an ‘identity instance’¹ for Outputable?

class Outputable a where
  ppr :: a -> SDoc

instance Outputabe SDoc where
  ppr :: SDoc -> SDoc
  ppr = id

A benefit: lets me always use pprTraceIt :: Outputable a => String -> a -> a, I know I can use pprTrace but I like not having to think about the type of what I'm tracing and neither functions work to debug something like Either SDoc Name.

---

¹ For lack of a better term, something like

class Foo a where
  foo :: a -> A

instance Foo A where
  foo :: A -> A
  foo = id @A

Trac metadata

Trac field	Value
Version	8.0.1
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	GHC API
Test case
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changed weight to 5

added GHC API Tfeature request Trac import labels

I've wondered this, too, thinking that the reason was to support better hygiene. But I think we should just have it.

Done in !778 (merged).

closed

added Pnormal label