[GHC] #16259: Hadrian does not work with a cabal v2-installed "Happy"

[GHC]

#16259: Hadrian does not work with a cabal v2-installed "Happy"
-------------------------------------+-------------------------------------
        Reporter:  RolandSenn        |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Build System      |              Version:  8.6.3
  (Hadrian)                          |
      Resolution:                    |             Keywords:
Operating System:  Linux             |         Architecture:
 Type of failure:  Building GHC      |  Unknown/Multiple
  failed                             |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by hvr):

 Ok, so the problem here is that `happy` gets demoted into an inplace
 package (and this basically means that the resulting executable can't be
 invoked without setting a couple of env-vars, which `cabal {run,exec}`
 would do -- but if you don't invoke it that way you'd be responsible for
 doing this... long story), because it picked up a local dependency, namely
 the intree-`Cabal` for its `setup-depends`; a simple way to workaround
 this is inject a constraint to prevent Setup.hs scripts from using an
 unreleased version of lib:Cabal, via e.g.

 {{{#!diff
 diff --git a/hadrian/cabal.project b/hadrian/cabal.project
 index 176d1ee..d8e5e79 100644
 --- a/hadrian/cabal.project
 +++ b/hadrian/cabal.project
 @@ -1,2 +1,4 @@
  packages: ./
            ../libraries/Cabal/Cabal/
 +
 +constraints: setup.Cabal < 2.5
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16259#comment:3>
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