Accessing shadowed definitions in GHCi

Apparently GHCi creates a qualified namespace for each line it interprets, as can be observed with:

> data A = A
> data A = B
> :t A
A :: Ghci3.A

Apparently accessing shadowed definitions in this way sometimes breaks GHCi:

> let a = a
> let a = a
> :t Ghci7.a

<interactive>:1:1: error:
    • GHC internal error: ‘Ghci7.a’ is not in scope during type checking, but it passed the renamer
      tcl_env of environment: []
    • In the expression: Ghci7.a

More specifically, complete reproduction instructions:

GHCi, version 8.1.20160205: http://www.haskell.org/ghc/  :? for help
> let foo = foo
> :t Ghci1.foo
Ghci1.foo :: t
> let foo = foo
> :t Ghci1.foo

<interactive>:1:1: error:
    • GHC internal error: ‘Ghci1.foo’ is not in scope during type checking, but it passed the renamer
      tcl_env of environment: []
    • In the expression: Ghci1.foo

1. 10.2 (and 7.8.3 as verified over IRC by monochrom) appears to have a slightly different behavior. It seems it only creates namespaces for data/newtype/class declarations. Yet still, it fails with an error the first time but works completely fine thereafter:

> data A = A
> data A = A
> :t Ghci1.A
Failed to load interface for ‘Ghci1’
no package key matching ‘interactive’ was found
> :t Ghci1.A
Ghci1.A :: Ghci1.A

1. 6.3 uses a different approach to displaying out of scope names so the behavior doesn't apply:

> data A = A
> data A = B
> :t A
A :: main::Interactive.A

Trac metadata

Trac field	Value
Version	8.0.1-rc1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	GHCi
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