[commit: ghc] master: Fix unsafe usage of `is_iloc` selector in Ord instance for ImportSpec (6e4188a)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/6e4188abf36d3b489ff7c9586ca49fe922f2beb7/ghc

>---------------------------------------------------------------

commit 6e4188abf36d3b489ff7c9586ca49fe922f2beb7
Author: Matthew Pickering <matthewtpickering at gmail.com>
Date:   Tue Dec 6 18:09:55 2016 +0000

    Fix unsafe usage of `is_iloc` selector in Ord instance for ImportSpec
    
    Summary:
    This fixes tests rn017, T7672 and closed #12930.
    
    Both these tests were self referential module imports through hs-boot
    files. As a result, I am quite suspicious of what the ImpAll constructor is
    used for. I had a brief hunt around but couldn't immediately see whether
    it was necessary.
    
    Reviewers: austin, bgamari
    
    Subscribers: simonpj, thomie, nomeata
    
    Differential Revision: https://phabricator.haskell.org/D2793
    
    GHC Trac Issues: #12930


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6e4188abf36d3b489ff7c9586ca49fe922f2beb7
 compiler/basicTypes/RdrName.hs | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/compiler/basicTypes/RdrName.hs b/compiler/basicTypes/RdrName.hs
index d60522f..c4e3228 100644
--- a/compiler/basicTypes/RdrName.hs
+++ b/compiler/basicTypes/RdrName.hs
@@ -1137,7 +1137,12 @@ instance Eq ImpItemSpec where
   p1 == p2 = case p1 `compare` p2 of EQ -> True; _ -> False
 
 instance Ord ImpItemSpec where
-   compare is1 is2 = is_iloc is1 `compare` is_iloc is2
+   compare is1 is2 =
+    case (is1, is2) of
+      (ImpAll, ImpAll) -> EQ
+      (ImpAll, _)      -> GT
+      (_, ImpAll)      -> LT
+      (ImpSome _ l1, ImpSome _ l2) -> l1 `compare` l2
 
 
 bestImport :: [ImportSpec] -> ImportSpec