From 1a54459c105754304f5036757b497011e9b8f7ec Mon Sep 17 00:00:00 2001
From: Ivan Trubach <mr.trubach@icloud.com>
Date: Thu, 15 Jun 2023 05:50:06 +0300
Subject: [PATCH] rubyPackages.pg: use pkg-config instead of pg_config

This change forces pg native extension to use pkg-config to locate libpq
instead of running pg_config. It also removes an unnecessary reference
to postgresql package since build flags are embedded in the output at
`$out/${ruby.gemPath}/build_info/*`.
---
 pkgs/development/ruby-modules/gem-config/default.nix | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/pkgs/development/ruby-modules/gem-config/default.nix b/pkgs/development/ruby-modules/gem-config/default.nix
index 22794da25167..a9eb1f96ab84 100644
--- a/pkgs/development/ruby-modules/gem-config/default.nix
+++ b/pkgs/development/ruby-modules/gem-config/default.nix
@@ -573,9 +573,14 @@ in
   };
 
   pg = attrs: {
-    buildFlags = [
-      "--with-pg-config=${postgresql}/bin/pg_config"
-    ];
+    # Force pkg-config lookup for libpq.
+    # See https://github.com/ged/ruby-pg/blob/6629dec6656f7ca27619e4675b45225d9e422112/ext/extconf.rb#L34-L55
+    #
+    # Note that setting --with-pg-config=${postgresql}/bin/pg_config would add
+    # an unnecessary reference to the entire postgresql package.
+    buildFlags = [ "--with-pg-config=ignore" ];
+    nativeBuildInputs = [ pkg-config ];
+    buildInputs = [ postgresql ];
   };
 
   psych = attrs: {