[GHC] #2182: ghc sessions (--make, --interactive, ghc api) erroneously retain instances

[GHC]

#2182: ghc sessions (--make, --interactive, ghc api) erroneously retain instances
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              Reporter:  claus       |            Owner:  ezyang
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:  7.10.1
             Component:  Compiler    |          Version:  6.9
  (Type checker)                     |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:  GHC         |  Related Tickets:
  accepts invalid program            |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Changes (by ezyang):

 * cc: simonpj (added)
 * owner:   => ezyang


Comment:

 Plan changed again! Now the idea is to maintain the set of orphan modules
 reachable from DIRECTLY imported modules, instead of the set of interface
 files.

 This ALMOST works. The big problem is when we mkLocalInstance, we need to
 know (immediately) if it's an orphan or not, because that entry in the
 instance environment may become enshrined forever if we have a GHCi
 session involved. I think we can pull this off by moving the logic from
 MkIface for calculating if an instance is an orphan to the typechecker.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/2182#comment:9>
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