Build without GHC environment files, instead using wrappers

Lets development shells work.

Author: rvl

builder/comp-builder.nix

@@ -221,7 +221,6 @@ stdenv.mkDerivation ({
   };
 
   CABAL_CONFIG = configFiles + /cabal.config;
-  GHC_ENVIRONMENT = configFiles + /ghc-environment;
   LANG = "en_US.UTF-8";         # GHC needs the locale configured during the Haddock phase.
   LC_ALL = "en_US.UTF-8";
 
@@ -232,7 +231,7 @@ stdenv.mkDerivation ({
     ++ component.pkgconfig;
 
   nativeBuildInputs =
-    [ghc buildPackages.removeReferencesTo]
+    [shellWrappers buildPackages.removeReferencesTo]
     ++ lib.optional (component.pkgconfig != []) pkgconfig
     ++ executableToolDepends;
 

builder/with-package-wrapper.nix

@@ -10,15 +10,15 @@
 }:
 
 let
-  isGhcjs       = ghc.isGhcjs or false;
+  isGhcjs        = ghc.isGhcjs or false;
   ghcCommand'    = if isGhcjs then "ghcjs" else "ghc";
-  ghcCommand = "${ghc.targetPrefix}${ghcCommand'}";
-  ghcCommandCaps= lib.toUpper ghcCommand';
-  libDir        = "$out/lib/${ghcCommand}-${ghc.version}";
-  docDir        = "$out/share/doc/ghc/html";
-  packageCfgDir = "${libDir}/package.conf.d";
+  ghcCommand     = "${ghc.targetPrefix}${ghcCommand'}";
+  ghcCommandCaps = lib.toUpper ghcCommand';
+  libDir         = "$out/lib/${ghcCommand}-${ghc.version}";
+  docDir         = "$out/share/doc/ghc/html";
+  packageCfgDir  = "${libDir}/package.conf.d";
 
-in runCommand "${ghc.name}-with-${package.identifier.name}" {
+in runCommand "${ghc.name}-for-${package.identifier.name}" {
   preferLocalBuild = true;
   passthru = {
     inherit (ghc) version meta;
@@ -32,49 +32,56 @@ in runCommand "${ghc.name}-with-${package.identifier.name}" {
     # Start with a ghc...
     mkdir -p $out/bin
     ${lndir}/bin/lndir -silent ${ghc} $out
-
-    # ...and replace package database with the one from target package config.
-    rm -rf ${libDir}
-    mkdir -p ${libDir}
-    # ... yet retain the lib/.../bin directory. This contains `unlit' and friends.
-    ${lndir}/bin/lndir -silent ${ghc}/lib/${ghcCommand}-${ghc.version}/bin ${libDir}
-
+    # ... remove all of the package directories
+    rm -rf ${libDir}/*/
+    # ... but retain the lib/ghc/bin directory. This contains `unlit' and friends.
+    ln -s ${ghc}/lib/${ghcCommand}-${ghc.version}/bin ${libDir}
+    # Replace the package database with the one from target package config.
     ln -s ${configFiles}/package.conf.d ${packageCfgDir}
 
     # Wrap compiler executables with correct env variables.
     # The NIX_ variables are used by the patched Paths_ghc module.
-    # The GHC_ENVIRONMENT variable forces ghc to use the build
-    # dependencies of the component.
 
-    for prg in ${ghcCommand} ${ghcCommand}i ${ghcCommand}-${ghc.version} ${ghcCommand}i-${ghc.version} runghc runhaskell; do
+    for prg in ${ghcCommand} ${ghcCommand}i ${ghcCommand}-${ghc.version} ${ghcCommand}i-${ghc.version}; do
       if [[ -x "${ghc}/bin/$prg" ]]; then
         rm -f $out/bin/$prg
         makeWrapper ${ghc}/bin/$prg $out/bin/$prg                           \
+          --add-flags '"-B$NIX_${ghcCommandCaps}_LIBDIR"'                   \
           --set "NIX_${ghcCommandCaps}"        "$out/bin/${ghcCommand}"     \
           --set "NIX_${ghcCommandCaps}PKG"     "$out/bin/${ghcCommand}-pkg" \
           --set "NIX_${ghcCommandCaps}_DOCDIR" "${docDir}"                  \
-          --set "NIX_${ghcCommandCaps}_LIBDIR" "${libDir}"                  \
-          --set "${ghcCommandCaps}_ENVIRONMENT" "${configFiles}/ghc-environment"
+          --set "NIX_${ghcCommandCaps}_LIBDIR" "${libDir}"
       fi
     done
 
-    # Point ghc-pkg to the package database of the component using the
-    # GHC_PACKAGE_PATH variable.
-
-    for prg in ${ghcCommand}-pkg ${ghcCommand}-pkg-${ghc.version}; do
+    for prg in runghc runhaskell; do
       if [[ -x "${ghc}/bin/$prg" ]]; then
         rm -f $out/bin/$prg
-        makeWrapper ${ghc}/bin/$prg $out/bin/$prg \
-          --set "${ghcCommandCaps}_PACKAGE_PATH" "${configFiles}/package.conf.d"
+        makeWrapper ${ghc}/bin/$prg $out/bin/$prg                           \
+          --add-flags "-f $out/bin/${ghcCommand}"                           \
+          --set "NIX_${ghcCommandCaps}"        "$out/bin/${ghcCommand}"     \
+          --set "NIX_${ghcCommandCaps}PKG"     "$out/bin/${ghcCommand}-pkg" \
+          --set "NIX_${ghcCommandCaps}_DOCDIR" "${docDir}"                  \
+          --set "NIX_${ghcCommandCaps}_LIBDIR" "${libDir}"
       fi
     done
 
-    # fixme: check if this is needed
-    # haddock was referring to the base ghc, https://github.com/NixOS/nixpkgs/issues/36976
+    # Wrap haddock, if the base GHC provides it.
     if [[ -x "${ghc}/bin/haddock" ]]; then
       rm -f $out/bin/haddock
       makeWrapper ${ghc}/bin/haddock $out/bin/haddock    \
+        --add-flags '"-B$NIX_${ghcCommandCaps}_LIBDIR"'  \
         --set "NIX_${ghcCommandCaps}_LIBDIR" "${libDir}"
     fi
+
+    # Point ghc-pkg to the package database of the component using the
+    # --global-package-db flag.
+
+    for prg in ${ghcCommand}-pkg ${ghcCommand}-pkg-${ghc.version}; do
+      if [[ -x "${ghc}/bin/$prg" ]]; then
+        rm -f $out/bin/$prg
+        makeWrapper ${ghc}/bin/$prg $out/bin/$prg --add-flags "--global-package-db=${packageCfgDir}"
+      fi
+    done
   ''
 )