[commit: ghc] master: Tighten checking for associated type instances (8136a5c)

[git at git.haskell.org]

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

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/8136a5cbfcd24647f897a2fae9fcbda0b1624035/ghc

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

commit 8136a5cbfcd24647f897a2fae9fcbda0b1624035
Author: Simon Peyton Jones <simonpj at microsoft.com>
Date:   Mon Apr 18 15:14:40 2016 +0100

    Tighten checking for associated type instances
    
    This patch finishes off Trac #11450.  Following debate on that ticket,
    the patch tightens up the rules for what the instances of an
    associated type can look like.  Now they must match the instance
    header exactly. Eg
    
       class C a b where
        type T a x b
    
    With this class decl, if we have an instance decl
      instance C ty1 ty2 where ...
    then the type instance must look like
         type T ty1 v ty2 = ...
    with exactly
      - 'ty1' for 'a'
      -  'ty2' for 'b', and
      - a variable for 'x'
    
    For example:
    
      instance C [p] Int
        type T [p] y Int = (p,y,y)
    
    Previously we allowed multiple instance equations and now, in effect,
    we don't since they would all overlap.  If you want multiple cases,
    use an auxiliary type family.
    
    This is consistent with the treatment of generic-default instances,
    and the user manual always said "WARNING: this facility (multiple
    instance equations may be withdrawn in the future".
    
    I also improved error messages, and did other minor refactoring.


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

8136a5cbfcd24647f897a2fae9fcbda0b1624035
 compiler/rename/RnSource.hs                        |  40 +++-
 compiler/typecheck/TcDeriv.hs                      |  16 +-
 compiler/typecheck/TcInstDcls.hs                   |   8 +-
 compiler/typecheck/TcTyClsDecls.hs                 |  13 +-
 compiler/typecheck/TcValidity.hs                   | 251 ++++++++++++---------
 compiler/types/Type.hs                             |  12 -
 docs/users_guide/glasgow_exts.rst                  |  66 ++++--
 testsuite/tests/ghci/scripts/T4175.hs              |   4 +-
 testsuite/tests/ghci/scripts/T4175.stdout          |   9 +-
 testsuite/tests/ghci/scripts/T6018ghcifail.stderr  |  13 +-
 .../tests/indexed-types/should_compile/T10931.hs   |   2 +-
 .../indexed-types/should_fail/SimpleFail10.hs      |   3 +-
 .../indexed-types/should_fail/SimpleFail10.stderr  |  11 +
 .../tests/indexed-types/should_fail/SimpleFail9.hs |   5 +-
 .../indexed-types/should_fail/SimpleFail9.stderr   |   7 +
 .../tests/indexed-types/should_fail/T11450.hs      |   9 +
 .../tests/indexed-types/should_fail/T11450.stderr  |   7 +
 testsuite/tests/indexed-types/should_fail/all.T    |   5 +-
 testsuite/tests/polykinds/T10570.stderr            |  14 +-
 testsuite/tests/th/T9692.hs                        |   2 +-
 testsuite/tests/th/T9692.stderr                    |   4 +-
 testsuite/tests/typecheck/should_fail/T6018fail.hs |   4 +-
 .../tests/typecheck/should_fail/T6018fail.stderr   |  13 +-
 .../typecheck/should_fail/T6018failclosed.stderr   | 144 ++++++------
 24 files changed, 394 insertions(+), 268 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 8136a5cbfcd24647f897a2fae9fcbda0b1624035