[GHC] #8683: add "cpp program" and "cpp program options" to settings file

[GHC]

#8683: add "cpp program" and "cpp program options" to settings file
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        Reporter:  carter            |            Owner:
            Type:  feature request   |           Status:  patch
        Priority:  highest           |        Milestone:  7.8.1
       Component:  Compiler          |          Version:  7.8.1-rc2
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:  #8439
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Changes (by carter):

 * status:  new => patch


Comment:

 Ok, it all works!

 some notes

 a) you still have to build using clang / gcc as the choice in cpp  for GHC
 building, but the hooks are there to set it otherwise with --with-hs-cpp
 and --with-hs-cpp-flags, but various hard codings in the build system
 prevent ghc builds from succeeding. Its just those issue are more
 discoverable :-)

 b) ghc will correctly use the new fields in the settings file, as if
 invoked with -pgmP and -optP being passed in. I managed to build all of
 lens's deps successfully using CPPHS! I did hit a bug  in CPPHS wrt
 building Lens 4.0.7, but again thats an issue with using CPPHS, not with
 the patch

 c) Theres still lots of hardcoded GCC / CPP things in the build system

 d) this gives the core of whats needed to provide a bindist that doesn't
 use clang/gcc for CPP, though because of other issues that need to be
 address (and should become a new ticket perhaps), you can't as yet build
 GHC with a CPP thats not clang or gcc

 is there any documentation i should add?  (either to the places patched or
 the documentation somewhere in the manual / wiki)

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8683#comment:42>
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