[GHC] #11990: Custom Type Error not getting triggered in the nested Type function call

[GHC]

#11990: Custom Type Error not getting triggered in the nested Type function call
-------------------------------------+-------------------------------------
        Reporter:  magesh.b          |                Owner:
            Type:  bug               |               Status:  merge
        Priority:  normal            |            Milestone:  8.0.2
       Component:  Compiler          |              Version:  8.0.1-rc3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by Ben Gamari <ben@…>):

 In [changeset:"b75d1940dd3362382c0bc94018a9045c2def82a9/ghc"
 b75d1940/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="b75d1940dd3362382c0bc94018a9045c2def82a9"
 Be more aggressive when checking constraints for custom type errors.

 This fixes #11990.

 The current rule is simpler than before: if we encounter an unsolved
 constraint that contains any mentions of properly applied `TypeError`,
 then we report the type error.

 If there are multiple `TypeErrors`, then we just report one of them.

 Reviewers: simonpj, bgamari, austin

 Reviewed By: simonpj

 Subscribers: thomie

 Differential Revision: https://phabricator.haskell.org/D2151

 GHC Trac Issues: #11990
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11990#comment:3>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler