[GHC] #10982: Warn about unused pattern variables in type families

[GHC]

#10982: Warn about unused pattern variables in type families
-------------------------------------+-------------------------------------
        Reporter:  jstolarek         |                Owner:  msosn
            Type:  feature request   |               Status:  closed
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.11
      Resolution:  fixed             |             Keywords:  newcomer
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
                                     |  UnusedTyVarWarnings,
                                     |  UnusedTyVarWarningsNamedWCs
      Blocked By:                    |             Blocking:
 Related Tickets:  #11098            |  Differential Rev(s):  Phab:D1576
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"575a98e4d245c1e60526ed6d6711d96cea08e9d2/ghc"
 575a98e4/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="575a98e4d245c1e60526ed6d6711d96cea08e9d2"
 Refactor named wildcards (again)

 Michal's work on #10982, #11098, refactored the handling of named
 wildcards by making them more like ordinary type variables.

 This patch takes the same idea to its logical conclusion, resulting
 in a much tidier, tighter implementation.

 Read Note [The wildcard story for types] in HsTypes.

 Changes:

  * Named wildcards are ordinary type variables, throughout

  * HsType no longer has a data constructor for named wildcards
    (was NamedWildCard in HsWildCardInfo).  Named wildcards are
    simply HsTyVars

  * Similarly named wildcards disappear from Template Haskell

  * I refactored RnTypes to avoid polluting LocalRdrEnv with something
    as narrow as named wildcards.  Instead the named wildcard set is
    carried in RnTyKiEnv.

 There is a submodule update for Haddock.
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10982#comment:11>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler