[GHC] #15912: Output hadrian build data for cabal-helper tool support

[GHC]

#15912: Output hadrian build data for cabal-helper tool support
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           Reporter:  davide         |             Owner:  (none)
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:  8.6.3
          Component:  Build System   |           Version:  8.6.2
  (Hadrian)                          |
           Keywords:  cabal-helper   |  Operating System:  Unknown/Multiple
  hadrian tool support               |
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 As a step in the direction of adding tool support for ghc development we
 can output some meta data from Hadrian to better support the cabal-helper
 tool. Proposed changes:

 1. Add a <ghc-root>/cabal.helper file that points to the 3 stage build
 directories under the default Hadrian build dir: _build.
 2. Add a "--cabal-helper" command line option to Hadrian that enables this
 output.
 3. Output <build-root>/stage<x>/build.helper in JSON format containing per
 package:
     * .cabal file path relative to <ghc-root> (achieved by prefixing paths
 with $PROJECTDIR) e.g $PROJECTDIR/libraries/binary/binary.cabal
     * source path e.g. $PROJECTDIR/libraries/binary/binary.cabal
     * Build "dist directory", which is the directory containing the setup-
 config file generated by cabal on build. this is a relative path e.g.
 libraries/binary/setup-config

 ## TODO

 * decide on the naming of files

 ## Implementation

 * See:
   * Packages.ghcPackages
   * Hadrian.Package.pkgCabalFile

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15912>
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