[GHC] #12610: Emit tab warning promptly

[GHC]

#12610: Emit tab warning promptly
-------------------------------------+-------------------------------------
        Reporter:  dfeuer            |                Owner:  dalaing
            Type:  bug               |               Status:  patch
        Priority:  high              |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.0.1
  (Parser)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  warning at compile-time            |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D3584
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by Ben Gamari <ben@…>):

 In [changeset:"49012ebc9ed44a0b1f8de3781e15c8115d3074f8/ghc"
 49012ebc/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="49012ebc9ed44a0b1f8de3781e15c8115d3074f8"
 Print warnings on parser failures (#12610).

 Test Plan: validate

 Reviewers: austin, bgamari, simonmar, mpickering

 Reviewed By: mpickering

 Subscribers: mpickering, rwbarton, thomie

 GHC Trac Issues: #12610

 Differential Revision: https://phabricator.haskell.org/D3584
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12610#comment:12>
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