From 9f1504590d4e9fa533265ae9035668a3ef4dbc9c Mon Sep 17 00:00:00 2001
From: Javier Sagredo <jasataco@gmail.com>
Date: Mon, 18 Sep 2023 17:08:08 +0200
Subject: [PATCH] Set `PKG_CONFIG_ALLOW_SYSTEM_(CFLAGS|LIBS)` by default

---
 Cabal/src/Distribution/Simple/Program/Builtin.hs | 7 +++++++
 changelog.d/pkgconfig-envvars                    | 8 ++++++++
 2 files changed, 15 insertions(+)
 create mode 100644 changelog.d/pkgconfig-envvars

diff --git a/Cabal/src/Distribution/Simple/Program/Builtin.hs b/Cabal/src/Distribution/Simple/Program/Builtin.hs
index 1f3db0740f3..e604dbbe962 100644
--- a/Cabal/src/Distribution/Simple/Program/Builtin.hs
+++ b/Cabal/src/Distribution/Simple/Program/Builtin.hs
@@ -400,4 +400,11 @@ pkgConfigProgram :: Program
 pkgConfigProgram =
   (simpleProgram "pkg-config")
     { programFindVersion = findProgramVersion "--version" id
+    , programPostConf = \_ pkgConfProg ->
+        let programOverrideEnv' =
+              programOverrideEnv pkgConfProg
+                ++ [ ("PKG_CONFIG_ALLOW_SYSTEM_CFLAGS", Just "1")
+                   , ("PKG_CONFIG_ALLOW_SYSTEM_LIBS", Just "1")
+                   ]
+         in pure $ pkgConfProg{programOverrideEnv = programOverrideEnv'}
     }
diff --git a/changelog.d/pkgconfig-envvars b/changelog.d/pkgconfig-envvars
new file mode 100644
index 00000000000..9b570693a44
--- /dev/null
+++ b/changelog.d/pkgconfig-envvars
@@ -0,0 +1,8 @@
+synopsis: PkgConfig environment variables
+prs: #9134
+
+description: {
+
+- `cabal` invokes `pkg-config` with `PKG_CONFIG_ALLOW_SYSTEM_CFLAGS` and `PKG_CONFIG_ALLOW_SYSTEM_LIBS` set
+
+}