From 8af26e3af0d93232fbe0752318531a69764ca2d5 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

(cherry picked from commit 9f1504590d4e9fa533265ae9035668a3ef4dbc9c)
---
 Cabal/src/Distribution/Simple/Program/Builtin.hs | 14 +++++++++++---
 changelog.d/pkgconfig-envvars                    |  8 ++++++++
 2 files changed, 19 insertions(+), 3 deletions(-)
 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 5c615fd5f51..5bb324f388f 100644
--- a/Cabal/src/Distribution/Simple/Program/Builtin.hs
+++ b/Cabal/src/Distribution/Simple/Program/Builtin.hs
@@ -343,6 +343,14 @@ cppProgram :: Program
 cppProgram = simpleProgram "cpp"
 
 pkgConfigProgram :: Program
-pkgConfigProgram = (simpleProgram "pkg-config") {
-    programFindVersion = findProgramVersion "--version" id
-  }
+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
+
+}