[commit: ghc] master: Refactor DeriveAnyClass's instance context inference (639e702)

[git at git.haskell.org]

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

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/639e702b6129f501c539b158b982ed8489e3d09c/ghc

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

commit 639e702b6129f501c539b158b982ed8489e3d09c
Author: Ryan Scott <ryan.gl.scott at gmail.com>
Date:   Fri Feb 10 16:12:46 2017 -0500

    Refactor DeriveAnyClass's instance context inference
    
    Summary:
    Currently, `DeriveAnyClass` has two glaring flaws:
    
    * It only works on classes whose argument is of kind `*` or `* -> *` (#9821).
    * The way it infers constraints makes no sense. It basically co-opts the
      algorithms used to infer contexts for `Eq` (for `*`-kinded arguments) or
      `Functor` (for `(* -> *)`-kinded arguments). This tends to produce overly
      constrained instances, which in extreme cases can lead to legitimate things
      failing to typecheck (#12594). Or even worse, it can trigger GHC panics
      (#12144 and #12423).
    
    This completely reworks the way `DeriveAnyClass` infers constraints to fix
    these two issues. It now uses the type signatures of the derived class's
    methods to infer constraints (and to simplify them). A high-level description
    of how this works is included in the GHC users' guide, and more technical notes
    on what is going on can be found as comments (and a Note) in `TcDerivInfer`.
    
    Fixes #9821, #12144, #12423, #12594.
    
    Test Plan: ./validate
    
    Reviewers: dfeuer, goldfire, simonpj, austin, bgamari
    
    Subscribers: dfeuer, thomie
    
    Differential Revision: https://phabricator.haskell.org/D2961


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

639e702b6129f501c539b158b982ed8489e3d09c
 compiler/typecheck/TcDeriv.hs                      |  50 +--
 compiler/typecheck/TcDerivInfer.hs                 | 357 +++++++++++++++++----
 compiler/typecheck/TcDerivUtils.hs                 |  92 ++++--
 compiler/typecheck/TcSimplify.hs                   |   3 +-
 compiler/typecheck/TcType.hs                       |   6 +-
 docs/users_guide/8.2.1-notes.rst                   |  11 +
 docs/users_guide/glasgow_exts.rst                  |  72 ++++-
 .../tests/deriving/should_compile/T12144_1.hs      |   6 +
 .../tests/deriving/should_compile/T12144_2.hs      |  15 +
 testsuite/tests/deriving/should_compile/T12423.hs  |  10 +
 testsuite/tests/deriving/should_compile/T12594.hs  |  41 +++
 .../{should_fail => should_compile}/T9968a.hs      |   0
 .../tests/deriving/should_compile/T9968a.stderr    |   5 +
 testsuite/tests/deriving/should_compile/all.T      |   7 +-
 .../tests/deriving/should_fail/T10598_fail1.stderr |   6 -
 testsuite/tests/deriving/should_fail/T9968a.stderr |   6 -
 testsuite/tests/deriving/should_fail/all.T         |   1 -
 .../tests/deriving/should_fail/drvfail004.stderr   |  17 +-
 .../tests/deriving/should_fail/drvfail012.stderr   |  17 +-
 .../tests/typecheck/should_fail/tcfail046.stderr   |  31 +-
 .../tests/typecheck/should_fail/tcfail169.stderr   |  17 +-
 21 files changed, 579 insertions(+), 191 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 639e702b6129f501c539b158b982ed8489e3d09c