[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:  new
        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:                    |
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Comment (by snowleopard):

 Yes, we can run these Cabal commands and obtain the output using Shake's
 `cmd` function:

 https://hackage.haskell.org/package/shake-0.17.3/docs/Development-
 Shake.html#v:cmd

 In particular, see the example with `Stdout out <- cmd ...`.

 However, this makes Cabal a dependency of Hadrian even for users who are
 building Hadrian using Stack (e.g. using the `build.stack.bat` script).

 Could we instead use Hadrian's built-in path resolver `lookupInPath`? Have
 a look here:

 https://gitlab.haskell.org/ghc/ghc/blob/master/hadrian/src/Hadrian/Oracles/Path.hs#L18-22

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16120#comment:2>
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