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.

default.nix

@@ -43,7 +43,6 @@ let
       allOverlays.build-toolbox
       allOverlays.checked-shell-script
       allOverlays.gitignore
-      allOverlays.postgresql-libpq
       (allOverlays.haskell-packages { inherit compiler; })
       allOverlays.slocat
     ];

nix/libpq.nix

@@ -1,61 +0,0 @@
-# Creating a separate libpq package is is discussed in
-# https://github.com/NixOS/nixpkgs/issues/61580, but nixpkgs has not moved
-# forward, yet.
-# This package is passed to postgresql-libpq (haskell) which needs to be
-# cross-compiled to the static build and possibly other architectures as
-# as well. To reduce the number of dependencies that need to be built with
-# it, this derivation focuses on building the client libraries only. No
-# server, no tests.
-{ stdenv
-, lib
-, openssl
-, zlib
-, postgresql
-, pkg-config
-, tzdata
-}:
-
-stdenv.mkDerivation {
-  pname = "libpq";
-  inherit (postgresql) src version patches;
-
-  __structuredAttrs = true;
-  env.CFLAGS = "-fdata-sections -ffunction-sections"
-    + (if stdenv.cc.isClang then " -flto" else " -fmerge-constants -Wl,--gc-sections");
-
-  configureFlags = [
-    "--without-gssapi"
-    "--without-icu"
-    "--without-readline"
-    "--with-openssl"
-    "--with-system-tzdata=${tzdata}/share/zoneinfo"
-    "--sysconfdir=/etc/postgresql"
-  ];
-
-  nativeBuildInputs = [ pkg-config tzdata ];
-  buildInputs = [ openssl zlib ];
-
-  buildFlags = [ "submake-libpq" "submake-libpgport" ];
-
-  installPhase = ''
-    runHook preInstall
-
-    make -C src/bin/pg_config install
-    make -C src/common install
-    make -C src/include install
-    make -C src/interfaces/libpq install
-    make -C src/port install
-
-    rm -rfv $out/share
-
-    runHook postInstall
-  '';
-
-  outputs = [ "out" ];
-
-  meta = with lib; {
-    homepage = "https://www.postgresql.org";
-    description = "Client API library for PostgreSQL";
-    license = licenses.postgresql;
-  };
-}

nix/overlays/default.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/postgresql-libpq.nix

@@ -1,7 +0,0 @@
-_: super:
-{
-  # Depending on which nixpkgs version is pinned, libpq might either be available already - or not.
-  libpq = super.libpq or (super.callPackage ../libpq.nix {
-    postgresql = super.postgresql_16;
-  });
-}

nix/static.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 [