From 2112a50d802f3e2c4f1c0b82e285d713014413d5 Mon Sep 17 00:00:00 2001
From: Hamish Mackenzie <Hamish.K.Mackenzie@gmail.com>
Date: Wed, 21 May 2025 13:26:53 +1200
Subject: [PATCH 1/2] Fix #2365 missing pg_config

The `pg_config` executable was moved into its own derivation in `nixpkgs`.  This fix includes that derivation if present when the `pg` library is requested.
---
 lib/system-nixpkgs-map.nix | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/lib/system-nixpkgs-map.nix b/lib/system-nixpkgs-map.nix
index 53f31132f6..32cf325aa0 100644
--- a/lib/system-nixpkgs-map.nix
+++ b/lib/system-nixpkgs-map.nix
@@ -17,6 +17,7 @@ let
       lndir ${pkgs.buildPackages.gcc.cc} $out
     '')
   ] else [];
+  postgresqlLibs = [ postgresql ] ++ lib.optional (postgresql ? pg_config) postgresql.pg_config;
 in
 # -- linux
 { crypto = [ openssl ];
@@ -57,10 +58,10 @@ in
   bz2 = [ bzip2 ];
   util = [ utillinux ];
   magic = [ file ];
-  pgcommon = [ postgresql ];
-  pgport = [ postgresql] ;
-  pq = [ postgresql ];
-  libpq = [ postgresql ];
+  pgcommon = postgresqlLibs;
+  pgport = postgresqlLibs;
+  pq = postgresqlLibs;
+  libpq = postgresqlLibs;
   iconv = [ libiconv ];
   lapack = [ liblapack ];
   boost_atomic = [ boost ];

From 79d2b7b4f26befcbc61010bc9ca9df7044595904 Mon Sep 17 00:00:00 2001
From: Hamish Mackenzie <Hamish.K.Mackenzie@gmail.com>
Date: Wed, 21 May 2025 14:41:11 +1200
Subject: [PATCH 2/2] Add comment

---
 lib/system-nixpkgs-map.nix | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/lib/system-nixpkgs-map.nix b/lib/system-nixpkgs-map.nix
index 32cf325aa0..f979bfd0c1 100644
--- a/lib/system-nixpkgs-map.nix
+++ b/lib/system-nixpkgs-map.nix
@@ -17,6 +17,9 @@ let
       lndir ${pkgs.buildPackages.gcc.cc} $out
     '')
   ] else [];
+  # In newer versions of nixpkgs `pg_config` has been moved to its own derivation.
+  # Haskell libs that depend on the `pq` library (like `postgresql-libpq`)
+  # are likely to require `pg_config` to be in the `PATH` as well.
   postgresqlLibs = [ postgresql ] ++ lib.optional (postgresql ? pg_config) postgresql.pg_config;
 in
 # -- linux