[commit: ghc] ghc-8.2: Fix constraint simplification in rules (9869213)

[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/98692134c3aee35dd89992aff3c350f49543a67b/ghc

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

commit 98692134c3aee35dd89992aff3c350f49543a67b
Author: Simon Peyton Jones <simonpj at microsoft.com>
Date:   Fri Mar 10 12:09:52 2017 +0000

    Fix constraint simplification in rules
    
    Trac #13381 showed that we were losing track of a wanted constraint
    when simplifying the LHS constraints for a RULE.
    
    This patch fixes it, makes the code a bit simpler, and better
    documented.
    
    (cherry picked from commit af6ed4a62c77e57f544243aa72bba51a1cff6808)


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98692134c3aee35dd89992aff3c350f49543a67b
 compiler/typecheck/TcRules.hs                      | 153 +++++++++++----------
 testsuite/tests/typecheck/should_compile/T13381.hs |  22 +++
 .../tests/typecheck/should_compile/T13381.stderr   |  14 ++
 testsuite/tests/typecheck/should_compile/all.T     |   1 +
 4 files changed, 114 insertions(+), 76 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 98692134c3aee35dd89992aff3c350f49543a67b