ASSERT failed! when building ghc-debug-client with GHC HEAD

Attempting to build ghc-debug-client with GHC HEAD (as as commit fc24c5cf) using a GHC build with assertions enabled will throw an ASSERT failed! error. Here is a minimized version of ghc-debug-client that triggers the issue:

{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TupleSections #-}
{-# LANGUAGE TypeApplications #-}
module GHC.Debug.TypePointsFrom (detectLeaks) where

import Control.Monad (zipWithM_)
import Control.Monad.Reader (ReaderT(..))
import Control.Monad.State (StateT, evalStateT)
import qualified Data.Map as M
import qualified Data.Set as S

data Debuggee

newtype DebugM a = DebugM (ReaderT Debuggee IO a)
                    deriving (Functor, Applicative, Monad)

runSimple :: Debuggee -> DebugM a -> IO a
runSimple d (DebugM a) = runReaderT a d

cands :: [a]
cands = []
{-# NOINLINE cands #-}

detectLeaks :: Debuggee -> IO ()
detectLeaks e = loop M.empty
  where
    loop :: M.Map () RankInfo -> IO ()
    loop rm = do
      gs <- runSimple e $ mapM (findSlice rm) cands
      zipWithM_ (\n _g -> writeFile
                            ("slices/" ++ show @Int n ++ ".dot")
                            "abcd")
                [0..] gs
      loop rm

data RankInfo = RankInfo !Double !Int

lookupRM :: () -> M.Map () RankInfo -> [((), RankInfo)]
lookupRM k m = M.assocs filtered_map
  where
    (res_map, _) = M.partitionWithKey (\e _ -> e == k) m
    filtered_map = M.filter (\(RankInfo r _) -> r > 0) res_map

findSlice :: forall m a. Monad m => M.Map () RankInfo -> () -> m [a]
findSlice rm _k = evalStateT go S.empty
  where
    go :: StateT s m [a]
    go = do
      let next_edges = lookupRM () rm
      _ss <- concat <$> mapM (\_ -> go) next_edges
      return []

$ ~/Software/ghc-9.11.20240504/bin/ghc -O Bug.hs -fforce-recomp
[1 of 1] Compiling GHC.Debug.TypePointsFrom ( Bug.hs, Bug.o )
WARNING:
  Lost join point
  bndr: loop_s5Ch
  tc:
  rules: []
  Call stack:
      CallStack (from HasCallStack):
        warnPprTrace, called at compiler/GHC/Core/Opt/OccurAnal.hs:3902:5 in ghc-9.11-inplace:GHC.Core.Opt.OccurAnal
<no location info>: error:
    ASSERT failed!
  CallStack (from HasCallStack):
    assert, called at compiler/GHC/Core/Opt/OccurAnal.hs:3853:10 in ghc-9.11-inplace:GHC.Core.Opt.OccurAnal

added Tbug assertion failure needs triage labels

mentioned in merge request head.hackage!362 (merged)

changed the description

mentioned in commit 196b7070

mentioned in merge request !12576 (closed)

Great repro case thank you. Fix is in !12576 (closed)

mentioned in issue #24638 (closed)

mentioned in commit 5a02a27c

mentioned in commit 03c5dfbf

Fixed by

commit 03c5dfbf52969504ca3473cb2eb7b3f7cf96d4b3
Author: Simon Peyton Jones <simon.peytonjones@gmail.com>
Date:   Sat May 4 22:56:03 2024 +0100

    Fix a float-out error
    
    Ticket #24768 showed that the Simplifier was accidentally destroying
    a join point.  It turned out to be that we were sending a bottoming
    join point to the top, accidentally abstracting over /other/ join
    points.
    
    Easily fixed.

 compiler/GHC/Core/Opt/SetLevels.hs                 | 11 ++++++--
 testsuite/tests/simplCore/should_compile/T24768.hs | 56 ++++++++++++++++++++++++++++++++++++++++
 testsuite/tests/simplCore/should_compile/all.T     |  1 +
 3 files changed, 66 insertions(+), 2 deletions(-)

closed

mentioned in commit 113e76d3