[MacPorts] #62228: haskell-stack 1.0: set stack root to home directory

[MacPorts]

#62228: haskell-stack 1.0: set stack root to home directory
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 Reporter:  Ionic   |      Owner:  (none)
     Type:  defect  |     Status:  new
 Priority:  Normal  |  Milestone:
Component:  ports   |    Version:
 Keywords:          |       Port:
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 Stack root is currently defined as `${workpath}/.stack`.

 That's... okay, but leads to a weird issue (probably due to a bug in stack
 itself): during the destroot phase, it ignores this environment variable,
 uses `~/.stack` instead, re-downloads GHC, populates that directory and,
 worst of all, rebuilds all the packages.

 This rebuild is not just wasteful, but actually triggers a second bug in
 stack: it doesn't pass down GHC options (which I need for `legacy-support`
 integration) during `stack install`/`stack build --copy-bins`. So the
 rebuild will fail and I have no idea how to fix stack to pass down the
 given GHC options.

 Now, this said, we can easily fix that by defining the stack root relative
 to the home directory. This sounds a bit dangerous, but shouldn't be,
 since we set `$HOME` to `${workpath}/.home`.

 I could have committed this myself, but I'm looking for comments.

 Case in point: if I set `haskell_stack.stack_root
 "${workpath}/.home/.stack`, the second rebuild in the destroot phase
 vanishes completely.

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Ticket URL: <https://trac.macports.org/ticket/62228>
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