-ddump-splices omits required parentheses around quantified constraints
If you compile this program with `-ddump-splices`:
```hs
{-# LANGUAGE QuantifiedConstraints #-}
{-# LANGUAGE TemplateHaskell #-}
{-# OPTIONS_GHC -ddump-splices #-}
module Bug where
import Language.Haskell.TH
data Foo x = MkFoo x
$([d| f :: (forall a. Eq (Foo a)) => Foo x -> Foo x -> Bool
f = (==)
|])
```
You'll notice something fishy:
```
$ /opt/ghc/8.6.1/bin/ghci Bug.hs
GHCi, version 8.6.1: http://www.haskell.org/ghc/ :? for help
Loaded GHCi configuration from /home/rgscott/.ghci
[1 of 1] Compiling Bug ( Bug.hs, interpreted )
Bug.hs:(10,3)-(12,6): Splicing declarations
[d| f_a1Ia ::
(forall a_a1Ic. Eq (Foo a_a1Ic)) =>
Foo x_a1Ib -> Foo x_a1Ib -> Bool
f_a1Ia = (==) |]
======>
f_a5tj ::
forall a_a5tk. Eq (Foo a_a5tk) => Foo x_a5ti -> Foo x_a5ti -> Bool
f_a5tj = (==)
Ok, one module loaded.
```
The signature for `f` gets pretty-printed as:
```hs
f_a5tj :: forall a_a5tk. Eq (Foo a_a5tk) => Foo x_a5ti -> Foo x_a5ti -> Bool
```
Which is just plain wrong—there is a missing set of parentheses around the quantified constraint `forall a_a5tk. Eq (Foo a_a5tk)`.
Patch incoming.
<details><summary>Trac metadata</summary>
| Trac field | Value |
| ---------------------- | ---------------- |
| Version | 8.6.1 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Template Haskell |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture | |
</details>
<!-- {"blocked_by":[],"summary":"-ddump-splices omits required parentheses around quantified constraints","status":"New","operating_system":"","component":"Template Haskell","related":[],"milestone":"8.8.1","resolution":"Unresolved","owner":{"tag":"Unowned"},"version":"8.6.1","keywords":[],"differentials":[],"test_case":"","architecture":"","cc":[""],"type":"Bug","description":"If you compile this program with `-ddump-splices`:\r\n\r\n{{{#!hs\r\n{-# LANGUAGE QuantifiedConstraints #-}\r\n{-# LANGUAGE TemplateHaskell #-}\r\n{-# OPTIONS_GHC -ddump-splices #-}\r\nmodule Bug where\r\n\r\nimport Language.Haskell.TH\r\n\r\ndata Foo x = MkFoo x\r\n\r\n$([d| f :: (forall a. Eq (Foo a)) => Foo x -> Foo x -> Bool\r\n f = (==)\r\n |])\r\n}}}\r\n\r\nYou'll notice something fishy:\r\n\r\n{{{\r\n$ /opt/ghc/8.6.1/bin/ghci Bug.hs\r\nGHCi, version 8.6.1: http://www.haskell.org/ghc/ :? for help\r\nLoaded GHCi configuration from /home/rgscott/.ghci\r\n[1 of 1] Compiling Bug ( Bug.hs, interpreted )\r\nBug.hs:(10,3)-(12,6): Splicing declarations\r\n [d| f_a1Ia ::\r\n (forall a_a1Ic. Eq (Foo a_a1Ic)) =>\r\n Foo x_a1Ib -> Foo x_a1Ib -> Bool\r\n f_a1Ia = (==) |]\r\n ======>\r\n f_a5tj ::\r\n forall a_a5tk. Eq (Foo a_a5tk) => Foo x_a5ti -> Foo x_a5ti -> Bool\r\n f_a5tj = (==)\r\nOk, one module loaded.\r\n}}}\r\n\r\nThe signature for `f` gets pretty-printed as:\r\n\r\n{{{#!hs\r\nf_a5tj :: forall a_a5tk. Eq (Foo a_a5tk) => Foo x_a5ti -> Foo x_a5ti -> Bool\r\n}}}\r\n\r\nWhich is just plain wrong—there is a missing set of parentheses around the quantified constraint `forall a_a5tk. Eq (Foo a_a5tk)`.\r\n\r\nPatch incoming.","type_of_failure":"OtherFailure","blocking":[]} -->
issue