[commit: ghc] ghc-8.2: Fix #11400, #11560 by documenting an infelicity. (c722ff3)

[git at git.haskell.org]

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

On branch  : ghc-8.2
Link       : http://ghc.haskell.org/trac/ghc/changeset/c722ff338b5356c8e13bc3344140a9eb296afbc3/ghc

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

commit c722ff338b5356c8e13bc3344140a9eb296afbc3
Author: Richard Eisenberg <rae at cs.brynmawr.edu>
Date:   Thu Jun 1 18:09:05 2017 -0400

    Fix #11400, #11560 by documenting an infelicity.
    
    Really, the fix for both of these is #11307.
    
    (cherry picked from commit c9667d321c94ff0f67b73aa7bd560c38873f7df5)


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

c722ff338b5356c8e13bc3344140a9eb296afbc3
 docs/users_guide/glasgow_exts.rst | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/docs/users_guide/glasgow_exts.rst b/docs/users_guide/glasgow_exts.rst
index 3f039a2..9289637 100644
--- a/docs/users_guide/glasgow_exts.rst
+++ b/docs/users_guide/glasgow_exts.rst
@@ -8211,9 +8211,9 @@ enabled).
 The only way ``*`` is unordinary is in its parsing. In order to be backward
 compatible, ``*`` is parsed as if it were an alphanumeric idenfifier; note
 that we do not write ``Int :: (*)`` but just plain ``Int :: *``. Due to the
-bizarreness with which ``*`` is parsed-and the fact that it is the only such
-operator in GHC-there are some corner cases that are
-not handled. We are aware of two:
+bizarreness with which ``*`` is parsed--and the fact that it is the only such
+operator in GHC--there are some corner cases that are
+not handled. We are aware of three:
 
 - In a Haskell-98-style data constructor, you must put parentheses around
   ``*``, like this: ::
@@ -8227,6 +8227,10 @@ not handled. We are aware of two:
   Note that the keyword ``type`` there is just to disambiguate the import
   from a term-level ``(*)``. (:ref:`explicit-namespaces`)
 
+- In an instance declaration head (the part after the word ``instance``), you
+  must parenthesize ``*``. This applies to all manners of instances, including
+  the left-hand sides of individual equations of a closed type family.
+
 The ``Data.Kind`` module also exports ``Type`` as a synonym for ``*``.
 Now that type synonyms work in kinds, it is conceivable that we will deprecate
 ``*`` when there is a good migration story for everyone to use ``Type``.