[GHC] #14769: The RecompBecause [TH] check is not resume-build-safe

[GHC]

#14769: The RecompBecause [TH] check is not resume-build-safe
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        Reporter:  nh2               |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #481              |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by nh2):

 Replying to [comment:3 simonmar]:
 > you wouldn't perhaps consider Phabricator instead? It's much easier to
 review code there

 I will when I have it working and have some non-hacky commits; until then
 I prefer Github because it is much easier to update multi-commit patch
 series there than on Phab.

 > I'd be surprised if you can do that, we thought pretty hard about
 whether this was feasible and came to the conclusion that it probably
 wasn't, due to things like parallel builds, ghc --make needing to have
 unique supplies for multiple modules, and lazy I/O in the typechecker.

 I'm not convinced either yet that it will work, and the `'r'`
 `UniqueSupply` in the global `--make` `HscEnv` is giving me some troubles
 at the current state, but so far I haven't found a reason why maintaining
 an independent "seed" for each module (as we know all modules ahead of
 time in a `--make` invocation) wouldn't cover at least the cases of
 multiple modules and `-j`.

 Regarding the lazy I/O in the typechecker, could you point me at where
 that happens?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14769#comment:5>
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