Opened 6 months ago

#13777 new bug

Poor error message around CUSKs

Reported by: goldfire Owned by:
Priority: normal Milestone:
Component: Compiler Version: 8.2.1-rc2
Keywords: TypeInType, CUSKs Cc:
Operating System: Unknown/Multiple Architecture: Unknown/Multiple
Type of failure: None/Unknown Test Case:
Blocked By: Blocking:
Related Tickets: Differential Rev(s):
Wiki Page:

Description

While typing up comment:7:ticket:13761, I came across a poor error message around CUSKs.

data Proxy (a :: k) = P
data S :: forall k. Proxy k -> Type where
  MkS :: S (P :: Proxy Maybe)

produces

    You have written a *complete user-suppled kind signature*,
    but the following variable is undetermined: k0 :: *
    Perhaps add a kind signature.
    Inferred kinds of user-written variables:

That promised list of the kinds of user-written variables is empty. Either GHC should find something to print (like k :: k0, perhaps) or omit the header.

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