devshell: better definition of PKG_CONFIG_PATH

 that manually going through pkg-config of all packages.
 Also filter out non-derivation from nativeBuildInputs.

Author: jbgi

lib/project-overlays.nix

@@ -7,22 +7,17 @@
   devshell = final: prev: {
     devshell = let
     in {
-      packages = final.shell.nativeBuildInputs
-      # Cannot add the whole final.shell.buildInputs list because many collide with each other when fused.
-      # So we only add what is really used (by pkg-config):
-      ++ map (p: p.dev or p) (lib.concatLists (lib.concatMap (p: p.components.library.pkgconfig or [] ++ p.components.setup.pkgconfig or [] ++ lib.concatMap (c: lib.concatMap (a: a.pkgconfig) (lib.attrValues c)) (lib.attrValues (removeAttrs p.components ["library" "setup"])))
-        (lib.attrValues final.pkg-set.config.packages)))
+      packages = lib.filter lib.isDerivation (final.shell.nativeBuildInputs
       # devshell does not use pkgs.mkShell / pkgs.stdenv.mkDerivation,
       # so we need to explicit required dependencies which
       # are provided implicitely by stdenv when using the normal shell:
-      ++ (lib.filter lib.isDerivation final.shell.stdenv.defaultNativeBuildInputs)
+      ++ final.shell.stdenv.defaultNativeBuildInputs)
       ++ lib.optional final.shell.stdenv.targetPlatform.isGnu final.pkgs.buildPackages.binutils;
       # We need to expose all the necessary env variables:
       env = [
         {
           name = "PKG_CONFIG_PATH";
-          # devshell fuse every all `packages` into a single directory ($DEVSHELL_DIR), so we use it:
-          prefix = "$DEVSHELL_DIR/lib/pkgconfig";
+          value = lib.makeSearchPath "lib/pkgconfig" final.shell.buildInputs;
         }
       ] ++ lib.mapAttrsToList lib.nameValuePair ({
         inherit (final.shell) NIX_GHC_LIBDIR;