nix: Build only libpq instead of full postgresql package

default.nix

@@ -36,7 +36,7 @@ let
       allOverlays.build-toolbox
       allOverlays.checked-shell-script
       allOverlays.gitignore
-      allOverlays.postgresql-default
+      allOverlays.postgresql-libpq
       allOverlays.postgresql-legacy
       allOverlays.postgresql-future
       allOverlays.postgis

nix/libpq.nix

@@ -0,0 +1,57 @@
+# 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
+, libkrb5
+, icu
+, postgresql
+, pkg-config
+, tzdata
+}:
+
+stdenv.mkDerivation {
+  pname = "libpq";
+  inherit (postgresql) src version;
+
+  configureFlags = [
+    "--without-gssapi"
+    "--without-readline"
+    "--with-openssl"
+    "--with-system-tzdata=${tzdata}/share/zoneinfo"
+  ];
+
+  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

@@ -4,7 +4,7 @@
   gitignore = import ./gitignore.nix;
   haskell-packages = import ./haskell-packages.nix;
   postgis = import ./postgis.nix;
-  postgresql-default = import ./postgresql-default.nix;
+  postgresql-libpq = import ./postgresql-libpq.nix;
   postgresql-legacy = import ./postgresql-legacy.nix;
   postgresql-future = import ./postgresql-future.nix;
   slocat = import ./slocat.nix;

nix/overlays/haskell-packages.nix

@@ -1,4 +1,4 @@
-{ compiler, extraOverrides ? (final: prev: { }) }:
+{ compiler }:
 
 self: super:
 let
@@ -41,11 +41,14 @@ let
       # Marked as broken (?)
       fuzzyset = lib.markUnbroken prev.fuzzyset;
 
-      postgresql-libpq = lib.dontCheck prev.postgresql-libpq_0_10_0_0;
+      postgresql-libpq = lib.dontCheck
+        (prev.postgresql-libpq_0_10_0_0.override {
+          postgresql = super.libpq;
+        });
 
       hasql-pool = lib.dontCheck prev.hasql-pool_0_10;
 
-    } // extraOverrides final prev;
+    };
 in
 {
   haskell =

nix/overlays/postgresql-default.nix

@@ -1,5 +0,0 @@
-self: super:
-# Overlay that sets the default version of PostgreSQL.
-{
-  postgresql = super.postgresql_15;
-}

nix/overlays/postgresql-libpq.nix

@@ -0,0 +1,6 @@
+self: super:
+{
+  libpq = super.callPackage ../libpq.nix {
+    postgresql = super.postgresql_15;
+  };
+}

nix/static.nix

@@ -12,21 +12,6 @@ let
   inherit (pkgsCross) pkgsStatic;
   inherit (pkgsStatic.haskell) lib;
 
-  # postgresql doesn't build in the fully static overlay - but the default
-  # derivation is built with static libraries anyway.
-  libpq = (pkgsCross.postgresql.override {
-    # disable server-side only stuff to improve compilation times
-    enableSystemd = false;
-    jitSupport = false;
-
-    # disable gssapi support, because it leads to linking errors
-    gssSupport = false;
-  }).overrideAttrs (finalAttrs: prevAttrs: {
-    dontDisableStatic = true;
-    # Tests fail for initdb and other server-side code which we don't care about
-    doCheck = false;
-  });
-
   packagesStatic =
     pkgsStatic.haskell.packages."${compiler}".override (old: {
       ghc = pkgsStatic.pkgsBuildHost.haskell.compiler."${compiler}".override {
@@ -40,7 +25,9 @@ let
 
       overrides = pkgs.lib.composeExtensions old.overrides (final: prev: {
         postgresql-libpq = (prev.postgresql-libpq.override {
-          postgresql = libpq;
+          # postgresql doesn't build in the fully static overlay - but the default
+          # derivation is built with static libraries anyway.
+          postgresql = pkgsCross.libpq;
         }).overrideAttrs (finalAttrs: prevAttrs: {
           # Using use-pkg-config flag, because pg_config won't work when cross-compiling
           configureFlags = prevAttrs.configureFlags ++ [ "-fuse-pkg-config" ];