[GHC] #16120: Hadrian should use cabal build-tools installed Alex and Happy if necessary

[GHC]

#16120: Hadrian should use cabal build-tools installed Alex and Happy if necessary
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        Reporter:  adamse            |                Owner:  (none)
            Type:  feature request   |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Build System      |              Version:  8.6.3
  (Hadrian)                          |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |  https://gitlab.haskell.org/ghc/ghc/merge_requests/69
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Changes (by sgraf):

 * cc: mpickering (added)


Comment:

 I just wanted to point out that this makes for different behavior when
 doing `./configure` and `hadrian/build.cabal.sh -c`. Specifically, when
 opening a `nix-shell --pure
 https://github.com/alpmestan/ghc.nix/archive/master.tar.gz`, this pollutes
 the configured $PATH variable with cabal-specific paths in my user home.
 Doing just `./configure` doesn't do that.

 I don't see why we always want to use the happy and alex versions that
 were used to build Hadrian.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16120#comment:12>
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