[GHC] #14273: Typed holes' "valid substitutions" suggestions are oblivious to type class constraints

[GHC]

#14273: Typed holes' "valid substitutions" suggestions are oblivious to type class
constraints
-------------------------------------+-------------------------------------
        Reporter:  RyanGlScott       |                Owner:  Tritlo
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:  8.4.1
       Component:  Compiler (Type    |              Version:  8.3
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Poor/confusing    |  Unknown/Multiple
  error message                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #9091, #9479      |  Differential Rev(s):  Phab:D4315
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"1e14fd3ecfd468c3beddb2e5f992c358e1a798de/ghc"
 1e14fd3e/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="1e14fd3ecfd468c3beddb2e5f992c358e1a798de"
 Inform hole substitutions of typeclass constraints (fixes  #14273).

 This implements SPJ's suggestion on the ticket (#14273). We find the
 relevant constraints (ones that whose free unification variables are all
 mentioned in the type of the hole), and then clone the free unification
 variables of the hole and the relevant constraints. We then add a
 subsumption constraints and run the simplifier, and then check whether
 all the constraints were solved.

 Reviewers: bgamari

 Reviewed By: bgamari

 Subscribers: RyanGlScott, rwbarton, thomie, carter

 GHC Trac Issues: #14273

 Differential Revision: https://phabricator.haskell.org/D4315
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14273#comment:21>
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