Compute correct install directories for instantiated Backpack components

[ezyang]

Previously, we would compute elabInstallDirs once when configuring a
component, and then reuse the exactly same install directories for
every instantiation of the package.  But this is wrong, since we're
installing the header/object files for each instantiation to a different
directory.  We refactor install directory computation into a helper
function and then call it again at instantiation time to refresh
the install directories.

For some reason, this bug ONLY manifests for packages installed from
Hackage; it seems install dirs are not respected for inplace packages.

Fixes #6005

[ezyang]

cc @vmchale

[andrewthad]

Thanks for working on a fix for this! I've tried it out in a fresh container by cloning the branch, installing ghc-8.6.5, and running the bootstrap script to install cabal, and I get a different error than I used to. Here's the build log:

Configuring library 'sockets-datagram-receive' for sockets-0.5.0.0..
Warning: The package has an extraneous version range for a dependency on an
internal library: sockets -any && ==0.5.0.0 && ==0.5.0.0 && ==0.5.0.0, sockets
-any && ==0.5.0.0 && ==0.5.0.0 && ==0.5.0.0, sockets -any && ==0.5.0.0 &&
==0.5.0.0 && ==0.5.0.0. This version range includes the current package but
isn't needed as the current package's library will always be used.
Preprocessing library 'sockets-datagram-receive' for sockets-0.5.0.0..
Building library 'sockets-datagram-receive' instantiated with
  Datagram.Receive = <Datagram.Receive>
  Socket.Buffer = <Socket.Buffer>
  Socket.Interrupt = <Socket.Interrupt>
for sockets-0.5.0.0..
[1 of 4] Compiling Socket.Buffer[sig] ( dist/build/sockets-datagram-receive/autogen/Socket/Buffer.hsig, nothing )
[2 of 4] Compiling Datagram.Receive[sig] ( src-datagram-receive/Datagram/Receive.hsig, nothing )

src-datagram-receive/Datagram/Receive.hsig:7:1: warning: [-Wunused-imports]
    The import of ‘Data.Primitive.PrimArray.Offset’ is redundant
      except perhaps to import instances from ‘Data.Primitive.PrimArray.Offset’
    To import instances alone, use: import Data.Primitive.PrimArray.Offset()
  |
7 | import Data.Primitive.PrimArray.Offset (MutablePrimArrayOffset)
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

src-datagram-receive/Datagram/Receive.hsig:9:1: warning: [-Wunused-imports]
    The import of ‘CInt’ from module ‘Foreign.C.Types’ is redundant
  |
9 | import Foreign.C.Types (CSize,CInt)
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

src-datagram-receive/Datagram/Receive.hsig:10:1: warning: [-Wunused-imports]
    The import of ‘GHC.Exts’ is redundant
      except perhaps to import instances from ‘GHC.Exts’
    To import instances alone, use: import GHC.Exts()
   |
10 | import GHC.Exts (RealWorld)
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^

src-datagram-receive/Datagram/Receive.hsig:12:1: warning: [-Wunused-imports]
    The import of ‘Posix.Socket’ is redundant
      except perhaps to import instances from ‘Posix.Socket’
    To import instances alone, use: import Posix.Socket()
   |
12 | import Posix.Socket (SocketAddress,SocketAddressInternet)
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[3 of 4] Compiling Socket.Interrupt[sig] ( dist/build/sockets-datagram-receive/autogen/Socket/Interrupt.hsig, nothing )
[4 of 4] Compiling Datagram.Receive.Indefinite ( src-datagram-receive/Datagram/Receive/Indefinite.hs, nothing )
Installing internal library sockets-datagram-receive in /root/.cabal/store/ghc-8.6.5/incoming/new-2047/root/.cabal/store/ghc-8.6.5/sockets-0.5.0.0-495643d155551acae808a8d25d861888f010b4b962f2d1e8b05baa22ccb89342/lib
cabal: '/usr/local/bin/ghc' exited with an error:
Failed to load interface for ‘Data.Attoparsec.ByteString.Char8’
no unit id matching
‘attoparsec-0.13.2.3-1da906b1053cab59d5c799d20d77f038c525df8cf0400fb81ec6ece5a908f5c3’
was found

It's entirely possible that I messed up installing cabal. I've not installed cabal from github before, and I may have goofed.

[ezyang]

@andrewthad oh, that's an interesting error. Does it happen if your Backpack packages are all inplace? (Is this the repro instructions from the original issue?)

[andrewthad]

Sorry, I didn't follow my own instructions. With:

cabal install -w /opt/ghc/bin/ghc-8.8.1 --ghc-options='-dppr-debug' --lib sockets-0.5.0.0

It succeeds. Hooray!

[ezyang]

I need to version guard the test but it looks like everything else is good.

[hvr]

I need to version guard the test but it looks like everything else is good.

@ezyang fyi, I just pushed ff7f5df to your PR

[ezyang]

Thanks @hvr!