Invalid constructor names are accepted in data declarations

Earlier today, someone was asking on #haskell why the constructor name (^) wouldn't work in GADT definitions. My response was that (^) isn't a constructor name, but much to my surprise, GHC accepts such names in a regular data declaration:

data Foo = F | (^^^^) Int Int

This creates a Foo type and value constructor F, but no value constructor (^^^^). However, in 7.6.3, if DataKinds are enabled, both constructors appear at the type level.

In HEAD, the same definition is accepted, with only F existing at the value level, as before. But at the type level, both F and (^^^^) just generate errors that Foo is not a promotable type. At that point, I think there's no question that the declaration should just be ruled out.

Trac metadata

Trac field	Value
Version	7.6.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture