No skolem info panic on invalid type application (GHC 9+)

Summary

Getting a compiler crash with the message "No skolem info" on a sample snippet where I accidentally used an invalid type application on an expression.

I can confirm the bug does not happen on GHC 8.10.7. I tested it on GHC 9.2.1 and GHC 9.2.2 - the bug persists in both. I have not checked in 9.0.1.

Steps to reproduce

{-# LANGUAGE AllowAmbiguousTypes #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE UndecidableInstances #-}
{-# LANGUAGE UndecidableSuperClasses #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE DataKinds #-}

module Main where

import Generics.SOP
import Generics.SOP.NP (ana_NP)

-- | [0..n] but for NP and the `n` is derived from `xs`.
rangeNP :: All Top xs => NP (K Int) xs
rangeNP = ana_NP f (K 0)
  where
    f :: K Int (y : ys) -> (K Int y, K Int ys)
    f (K i) = (K i, K $ i + 1)

fieldNames :: forall a flds. (HasDatatypeInfo a, IsProductType a flds) => NP (K String) flds
fieldNames = case hd . constructorInfo . datatypeInfo $ Proxy @a of
  Record _ np -> hmap (K . fieldName) np
  -- This branch uses stuff like `--0`, `--1` and so on for argument names.
  _ -> hmap undefined rangeNP @flds

Notice that final line, hmap. It should actually be hmap undefined $ rangeNP @flds (don't mind the undefined, I was actually using a typed hole there but didn't want to involve type holes in here).

This produces-

$ cabal build
Build profile: -w ghc-9.2.2 -O1
In order, the following will be built (use -v for more details):
 - testHS-0.1.0.0 (exe:testHS) (first run)
Preprocessing executable 'testHS' for testHS-0.1.0.0..
Building executable 'testHS' for testHS-0.1.0.0..
[1 of 1] Compiling Main             ( src/Main.hs, /testHS/dist-newstyle/build/x86_64-linux/ghc-9.2.2/testHS-0.1.0.0/x/testHS/build/testHS/testHS-tmp/Main.o )

src/Main.hs:26:39: error:ghc: panic! (the 'impossible' happened)
  (GHC version 9.2.2:
        No skolem info:
  [flds_a73s[sk:1]]
  Call stack:
      CallStack (from HasCallStack):
        callStackDoc, called at compiler/GHC/Utils/Panic.hs:181:37 in ghc:GHC.Utils.Panic
        pprPanic, called at compiler/GHC/Tc/Errors.hs:2912:17 in ghc:GHC.Tc.Errors

Please report this as a GHC bug:  https://www.haskell.org/ghc/reportabug

Same thing for GHC 9.2.1.

On the other hand, GHC 8.10.7 handles it correctly-

$ cabal build
Build profile: -w ghc-8.10.7 -O1
In order, the following will be built (use -v for more details):
 - testHS-0.1.0.0 (exe:testHS) (first run)
Preprocessing executable 'testHS' for testHS-0.1.0.0..
Building executable 'testHS' for testHS-0.1.0.0..
[1 of 1] Compiling Main             ( src/Main.hs, /testHS/dist-newstyle/build/x86_64-linux/ghc-8.10.7/testHS-0.1.0.0/x/testHS/build/testHS/testHS-tmp/Main.o )

src/Main.hs:28:8: error:
    • Cannot apply expression of type ‘NP f'0 xs0’
      to a visible type argument ‘flds’
    • In the expression: hmap undefined rangeNP @flds
      In a case alternative: _ -> hmap undefined rangeNP @flds
      In the expression:
        case hd . constructorInfo . datatypeInfo $ Proxy @a of
          Record _ np -> hmap (K . fieldName) np
          _ -> hmap undefined rangeNP @flds
   |
28 |   _ -> hmap undefined rangeNP @flds
   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Which is indeed true.

Expected behavior

No crash, ideally. Would like same behavior as GHC 8.10.7.

Environment

• GHC version used: 9.2.1, 9.2.2

Does not happen on GHC 8.10.7.

I'm using generics-sop == 0.5.1.2, though I doubt it's directly related to generics-sop. I haven't managed to get a simpler (no dependencies) reproduction yet, sorry.

Optional:

• Operating System: Arch linux
• System Architecture: 5.17.1-arch1-1 x86_64 GNU/Linux