[commit: ghc] master: Make note of #12907 in 8.0.2 release notes (a452c6e)

[git at git.haskell.org]

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

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/a452c6e57a286f3b31f0e3fbef83cbea0cee8b34/ghc

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

commit a452c6e57a286f3b31f0e3fbef83cbea0cee8b34
Author: Ryan Scott <ryan.gl.scott at gmail.com>
Date:   Thu Dec 1 12:24:48 2016 -0500

    Make note of #12907 in 8.0.2 release notes
    
    Test Plan: Read it, commit it, merge it, ship it
    
    Reviewers: goldfire, bgamari, austin, hvr, simonpj
    
    Reviewed By: simonpj
    
    Subscribers: thomie
    
    Differential Revision: https://phabricator.haskell.org/D2774
    
    GHC Trac Issues: #12907


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

a452c6e57a286f3b31f0e3fbef83cbea0cee8b34
 docs/users_guide/8.0.2-notes.rst | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/docs/users_guide/8.0.2-notes.rst b/docs/users_guide/8.0.2-notes.rst
index 9bc78ea..fa7aa8d 100644
--- a/docs/users_guide/8.0.2-notes.rst
+++ b/docs/users_guide/8.0.2-notes.rst
@@ -86,6 +86,19 @@ Language
 
       instance {-# OVERLAPPING #-} Foo Int
 
+-  GHC now adheres more closely to the Haskell 2010 Report with respect to
+   defaulting rules. As a result, GHC will now reject some defaulting rules
+   which GHC 8.0.1 and earlier would accept. For example, this is now
+   rejected ::
+
+      module Foo where
+      default (Bool)
+
+   because when the :ghc-flag:`-XExtendedDefaultRules` extension is not
+   enabled, defaulting rules only work for the ``Num`` class, of which ``Bool``
+   is not an instance. To make GHC accept the above program, simply enable the
+   :ghc-flag:`-XExtendedDefaultRules` extension.
+
 Compiler
 ~~~~~~~~