[GHC] #11053: Add a warning for pattern synonyms without signatures

[GHC]

#11053: Add a warning for pattern synonyms without signatures
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        Reporter:  mpickering        |                Owner:  mpickering
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.2
      Resolution:                    |             Keywords:  newcomer
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Matthew Pickering <matthewtpickering@…>):

 In [changeset:"1883afb2eee88c828adf6aa8014bab64dd6e8096/ghc" 1883afb/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="1883afb2eee88c828adf6aa8014bab64dd6e8096"
 Implement -fwarn-missing-pat-syn-sigs

 This adds a warning when a pattern synonym is not accompanied by a
 signature in the style of `-fwarn-missing-sigs`.

 It is turned on by -Wall.

 If the user specifies, `-fwarn-missing-exported-signatures` with
 `-fwarn-missing-pat-syn-sigs` then it will only warn when the pattern
 synonym is exported.

 Test Plan: ./validate

 Reviewers: hvr, austin, bgamari

 Reviewed By: bgamari

 Subscribers: thomie

 Differential Revision: https://phabricator.haskell.org/D1596

 GHC Trac Issues: #11053
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11053#comment:2>
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