Panic in GHCi debugger with GADTs, PolyKinds and Phantom types

Potentially related: #10616 (closed) (I noticed this one first, and in simplifying the code it changed to that error - note TcUnify.hs vs TcType.hs)

The code

{-# LANGUAGE GADTs , PolyKinds #-}

data AppTreeT (a::k) where
  Con :: AppTreeT a
  App :: AppTreeT a -> AppTreeT b -> AppTreeT (a b)

tmt :: AppTreeT (Maybe Bool)
tmt = App (Con :: AppTreeT Maybe) Con

f :: AppTreeT a -> Bool
f (App (c@Con) _) = const True c
f _ = False

when loaded in ghci runs fine without breakpoints, but panics when breaking on f (App )c@Con) _) = ...:

*Main> f tmt
True
*Main> :break 11
Breakpoint 0 activated at DebuggerCrash2.hs:11:21-32
*Main> f tmt
ghc-stage2: panic! (the 'impossible' happened)
  (GHC version 7.11.20150708 for x86_64-unknown-linux):
        ASSERT failed! file compiler/typecheck/TcType.hs line 739 k_anx

It fails to load in 7.4.1: DebuggerCrash2.hs:3:19: parse error on input k'` It fails to load in 7.8.2:

DebuggerCrash2.hs:5:50:
    Kind occurs check
    The first argument of ‘a’ should have kind ‘k0’,
      but ‘b’ has kind ‘k0 -> k1’
    In the type ‘AppTreeT (a b)’
    In the definition of data constructor ‘App’
    In the data declaration for ‘AppTreeT’

It has the panic in both 7.10.1 and HEAD@d71b65f5

uname -a: Linux cam-05-unx 3.5.0-54-generic #81~precise1-Ubuntu SMP Tue Jul 15 04:02:22 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux

gcc -v:
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.6/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.6.3-1ubuntu5' --with-bugurl=file:///usr/share/doc/gcc-4.6/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.6 --enable-shared --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.6 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object --enable-plugin --enable-objc-gc --disable-werror --with-arch-32=i686 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5) 

With ghci-7.10.1 -v

GHCi, version 7.10.1: http://www.haskell.org/ghc/  :? for help
Glasgow Haskell Compiler, Version 7.10.1, stage 2 booted by GHC version 7.8.2
Using binary package database: /5playpen/t-bepric/ghc-7.10.1-build/inplace/lib/package.conf.d/package.cache
wired-in package ghc-prim mapped to ghc-prim-0.4.0.0-inplace
wired-in package integer-gmp mapped to integer-gmp-1.0.0.0-inplace
wired-in package base mapped to base-4.8.0.0-inplace
wired-in package rts mapped to builtin_rts
wired-in package template-haskell mapped to template-haskell-2.10.0.0-inplace
wired-in package ghc mapped to ghc-7.10.1-inplace
wired-in package dph-seq not found.
wired-in package dph-par not found.
Hsc static flags: 
Loading package ghc-prim-0.4.0.0 ... linking ... done.
*** gcc:
/usr/bin/gcc -fno-stack-protector -DTABLES_NEXT_TO_CODE -L/5playpen/t-bepric/ghc-7.10.1-build/libraries/integer-gmp2/dist-install/build --print-file-name libgmp.so
Loading package integer-gmp-1.0.0.0 ... linking ... done.
Loading package base-4.8.0.0 ... linking ... done.
wired-in package ghc-prim mapped to ghc-prim-0.4.0.0-inplace
wired-in package integer-gmp mapped to integer-gmp-1.0.0.0-inplace
wired-in package base mapped to base-4.8.0.0-inplace
wired-in package rts mapped to builtin_rts
wired-in package template-haskell mapped to template-haskell-2.10.0.0-inplace
wired-in package ghc mapped to ghc-7.10.1-inplace
wired-in package dph-seq not found.
wired-in package dph-par not found.
*** Chasing dependencies:
Chasing modules from: 
Stable obj: []
Stable BCO: []
unload: retaining objs []
unload: retaining bcos []
Ready for upsweep []
Upsweep completely successful.
*** Deleting temp files:
Deleting: 
*** Chasing dependencies:
Chasing modules from: *DebuggerCrash2.hs
Stable obj: []
Stable BCO: []
unload: retaining objs []
unload: retaining bcos []
Ready for upsweep
  [NONREC
      ModSummary {
         ms_hs_date = 2015-07-08 13:56:59 UTC
         ms_mod = Main,
         ms_textual_imps = [import (implicit) Prelude]
         ms_srcimps = []
      }]
*** Deleting temp files:
Deleting: 
compile: input file DebuggerCrash2.hs
Created temporary directory: /tmp/ghc22446_0
*** Checking old interface for Main:
[1 of 1] Compiling Main             ( DebuggerCrash2.hs, interpreted )
*** Parser:
*** Renamer/typechecker:
*** Desugar:
Result size of Desugar (before optimization)
  = {terms: 32, types: 72, coercions: 1}
Result size of Desugar (after optimization)
  = {terms: 26, types: 55, coercions: 0}
*** Simplifier:
Result size of Simplifier iteration=1
  = {terms: 24, types: 79, coercions: 2}
Result size of Simplifier = {terms: 21, types: 76, coercions: 2}
*** Tidy Core:
Result size of Tidy Core = {terms: 31, types: 109, coercions: 4}
*** CorePrep:
Result size of CorePrep = {terms: 45, types: 157, coercions: 5}
*** ByteCodeGen:
Upsweep completely successful.
*** Deleting temp files:
Deleting: /tmp/ghc22446_0/ghc22446_2.c /tmp/ghc22446_0/ghc22446_1.o
Warning: deleting non-existent /tmp/ghc22446_0/ghc22446_2.c
Warning: deleting non-existent /tmp/ghc22446_0/ghc22446_1.o
Ok, modules loaded: Main.
*Main> f tmt
*** Parser:
*** Desugar:
*** Simplify:
*** CorePrep:
*** ByteCodeGen:
True
*Main> :break 11
Breakpoint 0 activated at DebuggerCrash2.hs:11:21-32
*Main> f tmt
*** Parser:
*** Desugar:
*** Simplify:
*** CorePrep:
*** ByteCodeGen:
ghc-stage2: panic! (the 'impossible' happened)
  (GHC version 7.10.1 for x86_64-unknown-linux):
        ASSERT failed! file compiler/typecheck/TcType.hs line 730 k_an3

Trac metadata

Trac field	Value
Version	7.10.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	GHCi
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	hvr
Operating system
Architecture