[GHC] #7841: Stage1Only conditional program/package building

[GHC]

#7841: Stage1Only conditional program/package building
-------------------------------+--------------------------------------------
  Reporter:  elliottt          |          Owner:                  
      Type:  feature request   |         Status:  closed          
  Priority:  normal            |      Milestone:                  
 Component:  Build System      |        Version:  7.7             
Resolution:  worksforme        |       Keywords:  Stage1Only      
        Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple
   Failure:  None/Unknown      |     Difficulty:  Unknown         
  Testcase:                    |      Blockedby:                  
  Blocking:                    |        Related:                  
-------------------------------+--------------------------------------------

Comment(by igloo):

 Replying to [comment:3 elliottt]:
 > It looks like libraries/base_dist-install_NOT_NEEDED would prevent base
 from being built at all, instead of just with a specific stage of the
 compiler.

 `base` is only built with one specific stage of the compiler.

 For packages that are built with multiple stages, the distdir is different
 for each one. e.g. `libraries/terminfo_dist-boot` is built with stage 0,
 and `libraries/terminfo_dist-install` with stage 1.

 > In the case where stage 2 doesn't get build, what causes the RTS to
 build, without all_rts being a dependency of all?

 Nothing currently; I'll fix that.

 > I'm very interested in getting some version of Stage1Only working, and
 am happy to do the work to implement it.  Could you give me a little
 guidance so that I can submit a better patch?

 One way (untested) would probably be to add a check `ifneq "$(Stage1Only)
 $3" "YES 2"` before calling the helpers in `build-prog` and `build-
 package`, as well as defining `compiler_stage2_NOT_NEEDED=YES` and
 `ghc_stage2_NOT_NEEDED=YES`.

 An alternative would be to define lots of `_NOT_NEEDED` variables by
 iterating over `PACKAGE_STAGE2`. This would make the logic in the rules
 slightly simpler, but would probably be a little more verbose overall.

 I think the second would probably be slightly nicer on balance.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7841#comment:4>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler