[PATCH 0/2] native-search-paths for GHC

[ericbavier]

From: Eric Bavier <address@hidden>

The first of these patches lets search-path-as-list function correctly when a
pattern is given and the 'directory file type is specified.

The second adds a native-search-paths field to our ghc package.  It modifies
our haskell-build-system to install a package-specific package database with
each haskell library.  GHC insists on a binary package cache file called
'package.cache' to be in each directory listed in GHC_PACKAGE PATH, so we
uniquely name the package database directories, and use a file-pattern to add
those to GHC_PACKAGE_PATH.

The benefit of this over the current situation is that one gets the benefit of
`guix package --search-paths`.  Currently, after installing ghc packages, the
user needs to know to manually add
~/.guix-profile/lib/ghc-7.8.4/package.conf.d to their GHC_PACKAGE_PATH.  GHC
package recipes would no longer need to propagate runtime dependencies, and
'guix environment' also works nicely out-of-the-box::

$ guix environment --ad-hoc ghc ghc-attoparsec
$ ghc-pkg list
/gnu/store/...-ghc-mtl-2.1.3.1/lib/ghc-7.8.4/ghc-mtl-2.1.3.1.conf.d
   base-4.7.0.2
   ghc-prim-0.3.1.0
   integer-gmp-0.5.1.0
   mtl-2.1.3.1
   rts-1.0
   transformers-0.3.0.0
/gnu/store/...-ghc-regex-base-0.93.2/lib/ghc-7.8.4/ghc-regex-base-0.93.2.conf.d
   array-0.5.0.0
   base-4.7.0.2
   bytestring-0.10.4.0
...
/gnu/store/4vvmngz1w8ccm7v7mk4f4dxk45834464-ghc-attoparsec-0.13.0.0/lib/ghc-7.8.4/ghc-attoparsec-0.13.0.0.conf.d
   array-0.5.0.0
   attoparsec-0.13.0.0
...

Though, as you can see in this example, libraries may be listed more than
once.  As far as I can tell at this point, that is just an aesthetic detail.

Future work might involve filtering build-only library dependencies from the
generated package database.  We could probably also remove the ghc package
database creation during profile generation.

I'd be insterested in hearing others' thoughts on this approach.

Eric Bavier (2):
  utils: Have search-path-as-list pattern search for directories.
  gnu: ghc: Add GHC_PACKAGE_PATH native search path.

 gnu/packages/haskell.scm            |   6 +++
 guix/build/haskell-build-system.scm | 100 +++++++++++++++++++++++++++++-------
 guix/build/utils.scm                |   9 ++--
 guix/search-paths.scm               |   6 ---
 4 files changed, 93 insertions(+), 28 deletions(-)

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2.4.3