[commit: ghc] master: Improved data family export documentation (b138248)

[git at git.haskell.org]

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

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/b1382481ac14a9f8999321581eaf88148bd44415/ghc

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

commit b1382481ac14a9f8999321581eaf88148bd44415
Author: David Kraeutmann <kane at kane.cx>
Date:   Fri Dec 11 22:36:55 2015 +0100

    Improved data family export documentation
    
    Reviewers: simonpj, austin, bgamari
    
    Reviewed By: simonpj
    
    Subscribers: thomie
    
    Differential Revision: https://phabricator.haskell.org/D1587
    
    GHC Trac Issues: #11164


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

b1382481ac14a9f8999321581eaf88148bd44415
 compiler/rename/RnNames.hs        | 5 +++--
 docs/users_guide/glasgow_exts.rst | 5 +++++
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/compiler/rename/RnNames.hs b/compiler/rename/RnNames.hs
index d61c299..0024304 100644
--- a/compiler/rename/RnNames.hs
+++ b/compiler/rename/RnNames.hs
@@ -1223,8 +1223,9 @@ exports_from_avail Nothing rdr_env _imports _this_mod
   where
     -- #11164: when we define a data instance
     -- but not data family, re-export the family
-    -- Generally, whenever we export a part of a declaration,
-    -- export the declaration, too.
+    -- Even though we don't check whether this is actually a data family
+    -- only data families can locally define subordinate things (`ns` here)
+    -- without locally defining (and instead importing) the parent (`n`)
     fix_faminst (AvailTC n ns flds)
       | not (n `elem` ns)
       = AvailTC n (n:ns) flds
diff --git a/docs/users_guide/glasgow_exts.rst b/docs/users_guide/glasgow_exts.rst
index 0959337..9993618 100644
--- a/docs/users_guide/glasgow_exts.rst
+++ b/docs/users_guide/glasgow_exts.rst
@@ -6666,6 +6666,11 @@ adjustment for type families:
    associated types ``Tj``. The types need a keyword "``type``" to
    distinguish them from data constructors.
 
+-  Whenever there is no export list and a data instance is defined, the
+   corresponding data family type constructor is exported along with
+   the new data constructors, regardless of whether the data family
+   is defined locally or in another module.
+
 .. _data-family-impexp-examples:
 
 Examples