Document how GHC disambiguates between multiple COMPLETE sets
authorRyan Scott <ryan.gl.scott@gmail.com>
Mon, 25 Sep 2017 18:21:54 +0000 (14:21 -0400)
committerRyan Scott <ryan.gl.scott@gmail.com>
Mon, 25 Sep 2017 18:21:54 +0000 (14:21 -0400)
commit0e60cc1825aace414597b644731c30269994f7fb
tree42082c3542b86fd18fadc0c08d3c15d4af723dc1
parentabed9bf5008baf6b3e84251fe4d07de80c532ead
Document how GHC disambiguates between multiple COMPLETE sets

Summary:
Up until now, the knowledge of how GHC chooses which
`COMPLETE` set to use in the presence of multiple applicable
`COMPLETE` sets for a single data type constructor was only
documented in the GHC wiki. But this really should be advertised to
anyone who uses `COMPLETE` pragmas heavily, so per SPJ's advice in
https://ghc.haskell.org/trac/ghc/ticket/14253#comment:10, this adds
this wisdom to the GHC users' guide.

Test Plan: Read it

Reviewers: austin, bgamari

Subscribers: mpickering, rwbarton, thomie

GHC Trac Issues: #14253

Differential Revision: https://phabricator.haskell.org/D4005
compiler/deSugar/Check.hs
docs/users_guide/glasgow_exts.rst