nix: remove libpq overlay

We have fixed the static build of PostgreSQL upstream, so we don't need
our separate overlay anymore. One more step towards building a static
executable on other platforms.

Author: wolfgangwalther

default.nix

@@ -35,7 +35,6 @@ let
       allOverlays.build-toolbox
       allOverlays.checked-shell-script
       allOverlays.gitignore
-      allOverlays.postgresql-libpq
       (allOverlays.haskell-packages { inherit compiler; })
       allOverlays.slocat
     ];

nix/libpq.nix

@@ -3,6 +3,5 @@
   checked-shell-script = import ./checked-shell-script;
   gitignore = import ./gitignore.nix;
   haskell-packages = import ./haskell-packages.nix;
-  postgresql-libpq = import ./postgresql-libpq.nix;
   slocat = import ./slocat.nix;
 }

nix/overlays/default.nix

@@ -60,15 +60,20 @@ let
 
       jose-jwt = prev.jose-jwt_0_10_0;
 
-      postgresql-libpq = lib.dontCheck (prev.callHackageDirect
+      postgresql-libpq = lib.overrideCabal
+        (lib.dontCheck (prev.callHackageDirect
+          {
+            pkg = "postgresql-libpq";
+            ver = "0.10.1.0";
+            sha256 = "sha256-tXOMqCO8opMilI9rx0D+njqjIjbZsH168Bzb8Aq8Ff4=";
+          }
+          { }
+        ))
         {
-          pkg = "postgresql-libpq";
-          ver = "0.10.1.0";
-          sha256 = "sha256-tXOMqCO8opMilI9rx0D+njqjIjbZsH168Bzb8Aq8Ff4=";
-        }
-        {
-          postgresql = super.libpq;
-        });
+          configureFlags = [ "-fuse-pkg-config" ];
+          libraryPkgconfigDepends = [ super.postgresql_16 ];
+          librarySystemDepends = [ ];
+        };
     };
 in
 {

nix/overlays/haskell-packages.nix

@@ -18,23 +18,6 @@ let
         # Cross compiling with native bignum works better than with gmp
         enableNativeBignum = true;
       };
-
-      overrides = pkgs.lib.composeExtensions old.overrides (_: prev: {
-        postgresql-libpq = (lib.overrideCabal prev.postgresql-libpq {
-          # TODO: This section can be simplified when this PR has made it's way to us:
-          #  https://github.com/NixOS/nixpkgs/pull/286370
-          # Additionally, we need to use the default version in nixpkgs, otherwise the
-          # override will not be active as well.
-          # Using use-pkg-config flag, because pg_config won't work when cross-compiling
-          configureFlags = [ "-fuse-pkg-config" ];
-          # postgresql doesn't build in the fully static overlay - but the default
-          # derivation is built with static libraries anyway.
-          libraryPkgconfigDepends = [ pkgsStatic.libpq ];
-          librarySystemDepends = [ ];
-        }).overrideAttrs (_: prevAttrs: {
-          buildInputs = prevAttrs.buildInputs ++ [ pkgsStatic.openssl ];
-        });
-      });
     });
 
   makeExecutableStatic = drv: pkgs.lib.pipe drv [