[GHC] #13336: Improve or remove the glomming warning

[GHC]

#13336: Improve or remove the glomming warning
-------------------------------------+-------------------------------------
           Reporter:  mpickering     |             Owner:  (none)
               Type:  task           |            Status:  new
           Priority:  low            |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 In the GHC build log there's lots of warnings about "glomming" but they
 are not actionable.

 The first problem is understanding what glomming is, that much is
 explained in the `Note [Glomming]`,

 In my own words, in the occurence analyser there are situations where
 there are out of scope top-level bindings. This usually happens when a
 rule is fired which drops in a new binding which does not appear anywhere
 else other than in rules.

 GHC dutifully warns us about this event but I can't work out why it this
 is necessary. What is bad about glomming? It seems like normal and
 expected behaviour for this to happen, further, there isn't really
 anything you can do about it.

 If it is a worthwhile warning to investigate, then the debugging output
 should be improved as the output is currently a list of uniques with
 occurence information which is difficult to map to source files. It would
 be much more useful to display the user-level names of the glommed
 identifiers.

 For a real world example look in `Data.Maybe`, compiling this module with
 a debugging compiler will emit a warning about glomming because of
 `mapMaybeFB` which appears on the RHS of rules but not anywhere else in a
 module.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13336>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler