Andreas Herrmann authored Jun 07, 2018 and Ben Gamari committed Jun 07, 2018

Previously we would print code which would not round-trip:
```
> :set -XDataKinds
> :set -XPolyKinds
> data Proxy k = Proxy
> _ :: Proxy '[ 'True ]
error:
  Found hole: _ :: Proxy '['True]
> _ :: Proxy '['True]
error:
    Invalid type signature: _ :: ...
    Should be of form <variable> :: <type>
```

Test Plan: Validate with T14343

Reviewers: RyanGlScott, goldfire, bgamari, tdammers

Reviewed By: RyanGlScott, bgamari

Subscribers: tdammers, rwbarton, thomie, carter

GHC Trac Issues: #14343

Differential Revision: https://phabricator.haskell.org/D4746