Set HASKELL_GI paths

Author: hamishmack

builder/make-config-files.nix

@@ -1,4 +1,4 @@
-{ stdenv, lib, haskellLib, ghc, nonReinstallablePkgs, runCommand, writeText, writeScript }@defaults:
+{ pkgs, stdenv, lib, haskellLib, ghc, nonReinstallablePkgs, runCommand, writeText, writeScript }@defaults:
 
 { identifier, component, fullName, flags ? {}, needsProfiling ? false, enableDWARF ? false, chooseDrv ? drv: drv, nonReinstallablePkgs ? defaults.nonReinstallablePkgs }:
 
@@ -121,7 +121,21 @@ let
         fi
       fi
     done
+    ${ # Help haskell.nix find .gir and .typelib files when compiling for musl
+    lib.optionalString stdenv.hostPlatform.isMusl ''
 
+      for l in "''${pkgsHostTarget[@]}"; do
+        if [ -d "$l/share/gir-1.0" ]; then
+          HASKELL_GI_GIR_SEARCH_PATH="''${HASKELL_GI_GIR_SEARCH_PATH:+''${HASKELL_GI_GIR_SEARCH_PATH}:}$l/share/gir-1.0"
+        fi
+        if [ -d "$l/lib/girepository-1.0" ]; then
+          HASKELL_GI_TYPELIB_SEARCH_PATH="''${HASKELL_GI_TYPELIB_SEARCH_PATH:+''${HASKELL_GI_TYPELIB_SEARCH_PATH}:}$l/lib/girepository-1.0"
+        fi
+      done
+      export HASKELL_GI_GIR_SEARCH_PATH
+      export HASKELL_GI_TYPELIB_SEARCH_PATH
+
+    ''}
     ${ # Note: we pass `clear` first to ensure that we never consult the implicit global package db.
        # However in `cabal.config` `cabal` requires `global` to be first.
       flagsAndConfig "package-db" ["clear"]