[commit: ghc] master: Observe #13267 in release notes (740ecda)

[git at git.haskell.org]

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

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/740ecda32116abe84b6d7d4786b3e2ad9c8ba2a4/ghc

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

commit 740ecda32116abe84b6d7d4786b3e2ad9c8ba2a4
Author: Ryan Scott <ryan.gl.scott at gmail.com>
Date:   Sat Mar 11 15:46:20 2017 -0500

    Observe #13267 in release notes
    
    I noticed some code in the wild that broke due to the validity checking
    introduced in #13267, so we should be proactive and warn about it in the 8.2
    release notes.


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

740ecda32116abe84b6d7d4786b3e2ad9c8ba2a4
 docs/users_guide/8.2.1-notes.rst | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/docs/users_guide/8.2.1-notes.rst b/docs/users_guide/8.2.1-notes.rst
index b3dd2de..9a7236b 100644
--- a/docs/users_guide/8.2.1-notes.rst
+++ b/docs/users_guide/8.2.1-notes.rst
@@ -167,6 +167,16 @@ Compiler
 
     "StillWorks" forall x. f (Just x) = e
 
+- Type synonyms can no longer appear in the class position of an instance.
+  This means something like this is no longer allowed: ::
+
+    type ReadShow a = (Read a, Show a)
+    instance Read Foo
+    instance Show Foo
+    instance ReadShow Foo -- illegal
+
+  See :ghc-ticket:`13267`.
+
 GHCi
 ~~~~