[GHC] #15985: `pprint EqualityT` infinitely loops

[GHC]

#15985: `pprint EqualityT` infinitely loops
-------------------------------------+-------------------------------------
        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:  8.8.1
       Component:  Template Haskell  |              Version:  8.6.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D5403
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by Ryan Scott <ryan.gl.scott@…>):

 In [changeset:"89d80921d9328499ffca9877e7dea540350be9c1/ghc" 89d8092/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="89d80921d9328499ffca9877e7dea540350be9c1"
 Fix embarrassing infinite loop in pprParendType

 Summary:
 `pprParendType` was missing an explicit case for
 `EqualityT`, which caused it to fall through to a catch-all case
 that invokes `ppr`. But `ppr` itself does not have a case for a
 partial application of `EqualityT`, so //it// falls back to
 `pprParendType`, resulting in an infinite loop!

 The fix is simple: add a case for `EqualityT` in `pprParendType`.
 While I was in the neighborhood, I removed the catch-call case in
 `pprParendType` to make this sort of mistake less likely to happen
 in the future.

 Test Plan: make test TEST=T15985

 Reviewers: bgamari, monoidal, simonpj

 Reviewed By: monoidal, simonpj

 Subscribers: rwbarton, carter

 GHC Trac Issues: #15985

 Differential Revision: https://phabricator.haskell.org/D5403
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15985#comment:2>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler