SOONER
  - It seems like long compiles are blocking other compiles?
    Namely, Cmd.hs, but maybe it's just not very parallel there.
  - EOF from distributor problem

  - Test with shakefile.
  - Restart when given different static flags, so I don't have to rely on the
    shutdown timeout.  Or can I start another distributor?  I think I need to
    allocate another socket then.
  - Unix sockets probably don't work on windows.  I should use a port number
    socket, but can I do a local one so that the firewall software doesn't
    freak out?



Use ghc api to compile a given module and keep its info in memory.

HscEnv - keeps cache info, stored in a GhcMonad.Session

Hint:
  loadModules -> doLoad
  doLoad:
    GHC.setTargets
    GHC.load GHC.LoadAllTargets
    GHC.load is GhcMake.load

GhcMake:
  load -> load2: this appears to do the dependency chasing, I don't think I
  need that, but let's see how it compiles.
  upsweep -> upsweep_mod mod ->
    fix dflags hscTarget
    if stable -> return entry from old hpt
    stable, no entry -> compile_it (Just linkable) SourceUnmodifiedAndStable
    .o exists -> reload .hi, return it
    otherwise -> compile_it Nothing SourceModified

    compile_it:
      compile hsc_env summary' mod_index nmods mb_old_ifec mb_linkable
          src_modified
      winds up being:
      DriverPipeline.compile hsc_env summary' mod_index nmods
          Nothing Nothing SourceModified

    "stable" means the module doesn't need recompilation:
      all stable imports && old linkable does not exist or == on-disk .o
      &&  date(on-disk .o) > date(.hs)

  What's HomePackageTable?  upsweep takes it, looks like cache info

DriverPipeline:
  compile is under the compilation manager, so it doesn't use -o.
  compile hsc_env summary' mod_index nmods Nothing Nothing SourceModified

  compileFile uses outputFile
    oneShot, and exported
  called by ghc/Main.hs


  I think I want HscMain.hscCompileBatch, that's what has the
  "Compiling [...]" msg.
  compile gives default args to compile'

Check out Main.doMake, which runs --make

-o flag is outputFile dflags
-c sets stopBeforeMode StopLn and '-no-link'

Main:
  plain batch compile is StopBefore (p :: Phase) -> oneShot hsc_env p srcs
  Phase I think should be As assembler, but -c sets StopLn

  Mode: Right (Right mode) -> main' mode
  -c -> Right (Right (StopBefore StopLn))
  -S -> As


What I want is to keep the HscEnv around like --make, but not invoke any of
the dep analysis, and specifically to use compileFile so it pays attention to
outputFile.

So see what --make does first:
  DoMake -> doMake srcs
  StopBefore StopLn -> oneShot hsc_env StopLn srcs

  doMake:
    sets targets and calls GHC.load LoadAllTargets, but that's the part that
    ignores outputFile.
    So:

    compileFile hsc_env StopLn src
      but preserve hsc_env, and do 'load's thing where I put loaded stuff into
      hsc_env

      According to HscEnv, the HPT (HomePackageTable) is not loaded by
      compileFile, but it implies the others are.

So:

Instance of calling compile myself, can I do it at the 'load' level?  That has
the code to detect unneeded compiles and load interfaces.

GhcMake.load (LoadUpTo ModuleName)