[commit: ghc] master: Improve the desugaring of RULES, esp those from SPECIALISE pragmas (d4d4bef)

[git at git.haskell.org]

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

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/d4d4bef2a2a3b90e6c5cb3544e1c2057920ed572/ghc

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

commit d4d4bef2a2a3b90e6c5cb3544e1c2057920ed572
Author: Simon Peyton Jones <simonpj at microsoft.com>
Date:   Fri Aug 1 14:56:53 2014 +0100

    Improve the desugaring of RULES, esp those from SPECIALISE pragmas
    
    In the code for Trac #8331 we were not getting a complaint, but
    we *were* getting a terrible (and virtually useless) RULE, looking
    like
       useAbstractMonad (complicated-dictionary-expresion) = $fuseAbstractMonad
    where we wanted
       useAbstractMonad d = $fuseAbstractMonad
    
    This commit improves the desugaring algorithm.  More comments
    explain; see Note [Drop dictionary bindings on rule LHS]


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d4d4bef2a2a3b90e6c5cb3544e1c2057920ed572
 compiler/deSugar/DsBinds.lhs                       | 75 ++++++++++++++++++----
 testsuite/tests/simplCore/should_compile/T8331.hs  | 59 +++++++++++++++++
 .../tests/simplCore/should_compile/T8331.stderr    |  9 +++
 testsuite/tests/simplCore/should_compile/all.T     |  1 +
 4 files changed, 133 insertions(+), 11 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 d4d4bef2a2a3b90e6c5cb3544e1c2057920ed572