Quick and dirty build of simple shared libraries and collecting dependencies. This was designed to build custom Haskell handlers for nginx-haskell-module.

This module allows for building simple shared libraries with Cabal.

Below is a simple example.

File ngx_distribution_test.hs

{-# LANGUAGE TemplateHaskell #-}

module NgxDistributionTest where

import           NgxExport

import           Data.ByteString (ByteString)
import qualified Data.ByteString.Lazy.Char8 as C8L
import           Data.Aeson
import           Data.Maybe

incCnt :: ByteString -> C8L.ByteString
incCnt = C8L.pack . show . succ . fromMaybe (0 :: Int) . decodeStrict
ngxExportYY 'incCnt

File ngx-distribution-test.cabal

name:                       ngx-distribution-test
version:                    0.1.0.0
build-type:                 Custom
cabal-version:              1.24

custom-setup
  setup-depends:            base >= 4.8 && < 5
                          , ngx-export-distribution

library
  default-language:         Haskell2010
  build-depends:            base >= 4.8 && < 5
                          , ngx-export
                          , bytestring
                          , aeson

  ghc-options:             -Wall -O2 -no-keep-hi-files -no-keep-o-files

File Setup.hs

import NgxExport.Distribution
main = defaultMain

The configuration step requires that utilities patchelf and hslibdeps were found in the paths of environment variable $PATH.

Building is a bit cumbersome: it expects explicit option --prefix at the configuration step (which will be interpreted as the first part of the rpath by utility hslibdeps), and requires explicit ghc option -o at the build step which is as well used by hslibdeps as the name of the target library. The build also requires the explicit option for linkage against the Haskell RTS library.

Let's build the example with commands cabal v1-configure and cabal v1-build (the v2-commands should probably work as well).

$ cabal v1-configure --prefix=/var/lib/nginx
Resolving dependencies...
[1 of 1] Compiling Main             ( dist/setup/setup.hs, dist/setup/Main.o )
Linking ./dist/setup/setup ...
Configuring ngx-distribution-test-0.1.0.0...

$ cabal v1-build --ghc-options="ngx_distribution_test.hs -o ngx_distribution_test.so -lHSrts_thr-ghc$(ghc --numeric-version)"
[1 of 1] Compiling NgxDistributionTest ( ngx_distribution_test.hs, ngx_distribution_test.o )
Linking ngx_distribution_test.so ...
---> Collecting libraries
'/usr/lib64/libHSrts_thr-ghc8.10.5.so' -> 'x86_64-linux-ghc-8.10.5/libHSrts_thr-ghc8.10.5.so'
'/home/lyokha/.cabal/lib/x86_64-linux-ghc-8.10.5/libHSngx-export-1.7.5-JzTEmHewqdC9gGi6rzcAtt-ghc8.10.5.so' -> 'x86_64-linux-ghc-8.10.5/libHSngx-export-1.7.5-JzTEmHewqdC9gGi6rzcAtt-ghc8.10.5.so'
'/home/lyokha/.cabal/lib/x86_64-linux-ghc-8.10.5/libHSmonad-loops-0.4.3-8Lx5Hn3pTtO62yOPdPW77x-ghc8.10.5.so' -> 'x86_64-linux-ghc-8.10.5/libHSmonad-loops-0.4.3-8Lx5Hn3pTtO62yOPdPW77x-ghc8.10.5.so'
'/home/lyokha/.cabal/lib/x86_64-linux-ghc-8.10.5/libHSasync-2.2.4-ENjuIeC23kaKyMVDRYThP3-ghc8.10.5.so' -> 'x86_64-linux-ghc-8.10.5/libHSasync-2.2.4-ENjuIeC23kaKyMVDRYThP3-ghc8.10.5.so'
'/usr/lib64/libHSstm-2.5.0.1-ghc8.10.5.so' -> 'x86_64-linux-ghc-8.10.5/libHSstm-2.5.0.1-ghc8.10.5.so'
'/home/lyokha/.cabal/lib/x86_64-linux-ghc-8.10.5/libHSaeson-1.5.6.0-6XeGmWHoO3vJYEUW5PXPgC-ghc8.10.5.so' -> 'x86_64-linux-ghc-8.10.5/libHSaeson-1.5.6.0-6XeGmWHoO3vJYEUW5PXPgC-ghc8.10.5.so'

   ...

'/usr/lib64/libHSbase-4.14.2.0-ghc8.10.5.so' -> 'x86_64-linux-ghc-8.10.5/libHSbase-4.14.2.0-ghc8.10.5.so'
'/usr/lib64/libHSinteger-gmp-1.0.3.0-ghc8.10.5.so' -> 'x86_64-linux-ghc-8.10.5/libHSinteger-gmp-1.0.3.0-ghc8.10.5.so'
'/usr/lib64/libHSghc-prim-0.6.1-ghc8.10.5.so' -> 'x86_64-linux-ghc-8.10.5/libHSghc-prim-0.6.1-ghc8.10.5.so'

---> Patching ngx_distribution_test.so
/var/lib/nginx/x86_64-linux-ghc-8.10.5:/home/lyokha/.cabal/lib/x86_64-linux-ghc-8.10.5:/usr/lib64:/usr/lib64/ghc-8.10.5/rts

Now the current working directory contains new files ngx_distribution_test.so and ngx_distribution_test-0.1.0.0.tar.gz and a new directory x86_64-linux-ghc-8.10.5. The tar-file contains the patched shared library and the directory with dependent libraries: it is ready for installation in directory /var/lib/nginx at the target system.

With this building approach, the following list of drawbacks must be taken into account.

1. Utility hslibdeps collects only libraries prefixed with libHS.
2. Command cabal v1-clean only deletes directory dist, it does not delete build artifacts in the current working directory.
3. Behavior of Cabal commands other than configure, build and clean is not well defined.