[commit: ghc] ghc-8.2: Fix constraint solving for forall-types (7d9ca50)

[git at git.haskell.org]

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

On branch  : ghc-8.2
Link       : http://ghc.haskell.org/trac/ghc/changeset/7d9ca50e184f2bc5da531646673fa7eecfd39862/ghc

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

commit 7d9ca50e184f2bc5da531646673fa7eecfd39862
Author: Simon Peyton Jones <simonpj at microsoft.com>
Date:   Wed Jun 28 12:38:59 2017 +0100

    Fix constraint solving for forall-types
    
    Trac #13879 showed that when we were trying to solve
    
      (forall z1 (y1::z1). ty1)  ~  (forall z2 (y2:z2). ty2)
    
    we'd end up spitting out z1~z2 with no binding site for them.
    Those kind equalities need to be inside the implication.
    
    I ended up re-factoring the code for solving forall-equalities.
    It's quite nice now.
    
    (cherry picked from commit fae672f647fe00c303d8fb56971563c1a76ad04e)


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7d9ca50e184f2bc5da531646673fa7eecfd39862
 compiler/typecheck/TcCanonical.hs                  | 95 ++++++++++++++++-----
 compiler/typecheck/TcSMonad.hs                     | 98 +++++++++++-----------
 testsuite/tests/typecheck/should_compile/T13879.hs | 29 +++++++
 testsuite/tests/typecheck/should_compile/all.T     |  1 +
 .../tests/typecheck/should_fail/tcfail174.stderr   |  2 +-
 5 files changed, 152 insertions(+), 73 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 7d9ca50e184f2bc5da531646673fa7eecfd39862