[commit: ghc] ghc-8.4: Fix a nasty bug in the pure unifier (1132ec6)

[git at git.haskell.org]

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

On branch  : ghc-8.4
Link       : http://ghc.haskell.org/trac/ghc/changeset/1132ec683591eafa55e309cd01b9f4cb5524c7c5/ghc

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

commit 1132ec683591eafa55e309cd01b9f4cb5524c7c5
Author: Simon Peyton Jones <simonpj at microsoft.com>
Date:   Mon Feb 26 17:44:55 2018 +0000

    Fix a nasty bug in the pure unifier
    
    The pure unifier was building an infinite type, through a defective
    occurs check.  So GHC went into an infinite loop.
    
    Reason: we were neglecting the 'kco' part of the type, which
    'unify_ty' maintains.  Yikes.
    
    The fix is easy.  I refactored a bit to make it harder to
    go wrong in future.
    
    (cherry picked from commit e99fdf775540440c1c58dc5ade3c5984dc49246f)


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1132ec683591eafa55e309cd01b9f4cb5524c7c5
 compiler/types/Unify.hs                 | 59 ++++++++++++++++++---------------
 testsuite/tests/polykinds/T14846.hs     | 39 ++++++++++++++++++++++
 testsuite/tests/polykinds/T14846.stderr | 43 ++++++++++++++++++++++++
 testsuite/tests/polykinds/all.T         |  1 +
 4 files changed, 116 insertions(+), 26 deletions(-)

Diff suppressed because of size. To see it, use:

    git diff-tree --root --patch-with-stat --no-color --find-copies-harder --ignore-space-at-eol --cc 1132ec683591eafa55e309cd01b9f4cb5524c7c5