[commit: ghc] master: Don't replace type family instances with the same LHS in GHCi (#7102) (0abe736)

[git at git.haskell.org]

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

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/0abe7361249b0b4dc43dc66547451da8916b30bf/ghc

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

commit 0abe7361249b0b4dc43dc66547451da8916b30bf
Author: Reid Barton <rwbarton at gmail.com>
Date:   Sun Feb 5 20:24:06 2017 -0500

    Don't replace type family instances with the same LHS in GHCi (#7102)
    
    This fixes the easy part of #7102 by removing the logic that lets the
    user replace a type family instance with a new one with the same LHS.
    As discussed on that ticket, this is unsound in general. Better to have
    the user redefine the type family from scratch.
    
    The example from comment:7 involving loading modules into ghci is not
    fixed yet; it actually doesn't rely on the instances having the same LHS.
    This commit adds an expect_broken test for that example as well.
    
    Test Plan: T7102a for the fix; T7102 is the test not fixed yet
    
    Reviewers: dfeuer, austin, bgamari, goldfire
    
    Reviewed By: dfeuer
    
    Subscribers: dfeuer, thomie
    
    Differential Revision: https://phabricator.haskell.org/D2994


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

0abe7361249b0b4dc43dc66547451da8916b30bf
 compiler/main/HscTypes.hs                          |  5 +--
 compiler/typecheck/FamInst.hs                      | 21 +++++-------
 compiler/types/FamInstEnv.hs                       | 32 ++----------------
 docs/users_guide/ghci.rst                          | 38 +++++++++++++++++++---
 testsuite/tests/ghci/scripts/ghci046.script        |  1 +
 testsuite/tests/ghci/scripts/ghci046.stderr        |  5 +++
 testsuite/tests/ghci/scripts/ghci046.stdout        |  2 +-
 .../tests/indexed-types/should_fail/T7102.script   |  5 +++
 .../should_fail/T7102.stdout}                      |  0
 .../tests/indexed-types/should_fail/T7102A.hs      |  3 ++
 .../tests/indexed-types/should_fail/T7102B.hs      |  6 ++++
 .../tests/indexed-types/should_fail/T7102C.hs      |  6 ++++
 .../tests/indexed-types/should_fail/T7102a.script  |  4 +++
 .../tests/indexed-types/should_fail/T7102a.stderr  |  5 +++
 testsuite/tests/indexed-types/should_fail/all.T    |  2 ++
 15 files changed, 84 insertions(+), 51 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 0abe7361249b0b4dc43dc66547451da8916b30bf