[GHC] #13896: Use response file to invoke hsc2hs

[GHC]

#13896: Use response file to invoke hsc2hs
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        Reporter:  bgamari       |                Owner:  ckoparkar
            Type:  bug           |               Status:  new
        Priority:  normal        |            Milestone:  8.6.1
       Component:  hsc2hs        |              Version:  8.0.1
      Resolution:                |             Keywords:  newcomer
Operating System:  Windows       |         Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown  |            Test Case:
      Blocked By:                |             Blocking:
 Related Tickets:                |  Differential Rev(s):
       Wiki Page:                |
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Changes (by ckoparkar):

 * owner:  (none) => ckoparkar


Comment:

 Ben, I'd like to work on this. Mikhail (23Skidoo) outlined the solution
 [https://github.com/haskell/cabal/issues/3122#issuecomment-181585821
 here]:

 > We're probably bumping into the same command-line length restriction we
 did with Haddock. If this is the case, the solution is to add support for
 response files to hsc2hs and use that in Cabal.

 One way to implement this idea would be to have something similar to
 [https://github.com/haskell/haddock/blob/ghc-8.4/driver/ResponseFile.hs
 haddock's implementation] in `hsc2hs`. Or, we could also have just one
 implementation somewhere, and have `haddock` and `hsc2hs` use that.

 What's the proper place to house this in GHC ?  `base` or `process` seem
 like the obvious candidates. Although `haddock` doesn't seem to depend on
 `process` right now.

 I haven't looked at the specifics of implementing this, but the overall
 roadmap I'd follow would be:

 (1) Copy
 [https://github.com/haskell/haddock/blob/ghc-8.4/driver/ResponseFile.hs
 haddock's implementation] to either `base` or `process` (or somewhere else
 ?)

 (2) Use that in `hsc2hs` and `haddock` (and remove the relevant bits from
 `haddock`)

 (3) Update `Cabal` appropriately

 Does this sound like a good idea ?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13896#comment:3>
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