[commit: ghc] master: More comments on role subtyping, unsoundness fix. (4aada7a)

[git at git.haskell.org]

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

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/4aada7a6c13752652cfce5e04f015a8909553917/ghc

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

commit 4aada7a6c13752652cfce5e04f015a8909553917
Author: Edward Z. Yang <ezyang at cs.stanford.edu>
Date:   Sun Feb 26 20:15:30 2017 -0800

    More comments on role subtyping, unsoundness fix.
    
    Summary:
    - We incorrectly allowed subroling on injective data in
      some cases. There is now a test to check for this case, and a Note.
    
    - More commentary on how the subtyping with roles works.
    
    Signed-off-by: Edward Z. Yang <ezyang at cs.stanford.edu>
    
    Test Plan: validate
    
    Reviewers: goldfire, austin, simonpj, bgamari
    
    Subscribers: thomie
    
    Differential Revision: https://phabricator.haskell.org/D3222


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4aada7a6c13752652cfce5e04f015a8909553917
 compiler/typecheck/TcRnDriver.hs                   | 55 +++++++++++++++++++++-
 testsuite/tests/backpack/should_fail/all.T         |  2 +
 testsuite/tests/backpack/should_fail/bkpfail44.bkp | 10 ++++
 .../tests/backpack/should_fail/bkpfail44.stderr    | 23 +++++++++
 testsuite/tests/backpack/should_fail/bkpfail45.bkp | 23 +++++++++
 .../tests/backpack/should_fail/bkpfail45.stderr    | 22 +++++++++
 6 files changed, 134 insertions(+), 1 deletion(-)

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 4aada7a6c13752652cfce5e04f015a8909553917