GHC internal error when GADT return type mentions its own constructor name
Take the following program:
{-# LANGUAGE GADTs #-}
{-# LANGUAGE TypeInType #-}
module Bug where
data A (a :: k) where
MkA :: A MkA
On GHC 8.4.2, this is rejected with a sensible error message:
$ /opt/ghc/8.4.2/bin/ghc Bug.hs
[1 of 1] Compiling Bug ( Bug.hs, Bug.o )
Bug.hs:6:12: error:
• Data constructor ‘MkA’ cannot be used here
(it is defined and used in the same recursive group)
• In the first argument of ‘A’, namely ‘MkA’
In the type ‘A MkA’
In the definition of data constructor ‘MkA’
|
6 | MkA :: A MkA
| ^^^
On GHC HEAD, however, this causes a GHC internal error:
$ ghc2/inplace/bin/ghc-stage2 Bug.hs
[1 of 1] Compiling Bug ( Bug.hs, Bug.o )
Bug.hs:6:12: error:
• GHC internal error: ‘MkA’ is not in scope during type checking, but it passed the renamer
tcl_env of environment: [asv :-> Type variable ‘k’ = k :: *,
asw :-> Type variable ‘a’ = a :: k,
rqs :-> ATcTyCon A :: forall k. k -> *]
• In the first argument of ‘A’, namely ‘MkA’
In the type ‘A MkA’
In the definition of data constructor ‘MkA’
|
6 | MkA :: A MkA
| ^^^
Trac metadata
Trac field | Value |
---|---|
Version | 8.5 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler (Type checker) |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |