From 3afd3a3920b999f795ec73e6c9a9740b1eff132b Mon Sep 17 00:00:00 2001
From: Javier Sagredo <jasataco@gmail.com>
Date: Wed, 19 Jul 2023 13:22:36 +0200
Subject: [PATCH 1/2] Try each pkg-config query separatedly if returned list
 doesn't match query length

MinGW's pkg-config returns only one version even if queried for
multiple libraries.
---
 .../Distribution/Solver/Types/PkgConfigDb.hs  | 20 ++++++++++++-------
 changelog.d/pkgconfig-once                    |  8 ++++++++
 2 files changed, 21 insertions(+), 7 deletions(-)
 create mode 100644 changelog.d/pkgconfig-once

diff --git a/cabal-install-solver/src/Distribution/Solver/Types/PkgConfigDb.hs b/cabal-install-solver/src/Distribution/Solver/Types/PkgConfigDb.hs
index 11e6da847f0..00bc38c28c3 100644
--- a/cabal-install-solver/src/Distribution/Solver/Types/PkgConfigDb.hs
+++ b/cabal-install-solver/src/Distribution/Solver/Types/PkgConfigDb.hs
@@ -70,12 +70,18 @@ readPkgConfigDb verbosity progdb = handle ioErrorHandler $ do
         (pkgVersions, _errs, exitCode) <-
                      getProgramInvocationOutputAndErrors verbosity
                        (programInvocation pkgConfig ("--modversion" : pkgNames))
-        case exitCode of
-          ExitSuccess -> (return . pkgConfigDbFromList . zip pkgNames) (lines pkgVersions)
-          -- if there's a single broken pc file the above fails, so we fall back into calling it individually
-          _ -> do
-             info verbosity ("call to pkg-config --modversion on all packages failed. Falling back to querying pkg-config individually on each package")
-             pkgConfigDbFromList . catMaybes <$> mapM (getIndividualVersion pkgConfig) pkgNames
+        if exitCode == ExitSuccess && length pkgNames == length pkgList
+          then (return . pkgConfigDbFromList . zip pkgNames) (lines pkgVersions)
+          else
+          -- if there's a single broken pc file the above fails, so we fall back
+          -- into calling it individually
+          --
+          -- Also some implementations of @pkg-config@ do not provide more than
+          -- one package version, so if the returned list is shorter than the
+          -- requested one, we fall back to querying one by one.
+          do
+            info verbosity ("call to pkg-config --modversion on all packages failed. Falling back to querying pkg-config individually on each package")
+            pkgConfigDbFromList . catMaybes <$> mapM (getIndividualVersion pkgConfig) pkgNames
   where
     -- For when pkg-config invocation fails (possibly because of a
     -- too long command line).
@@ -92,7 +98,7 @@ readPkgConfigDb verbosity progdb = handle ioErrorHandler $ do
     getIndividualVersion pkgConfig pkg = do
        (pkgVersion, _errs, exitCode) <-
                getProgramInvocationOutputAndErrors verbosity
-                 (programInvocation pkgConfig ["--modversion",pkg])
+                 (programInvocation pkgConfig ["--modversion", pkg])
        return $ case exitCode of
          ExitSuccess -> Just (pkg, pkgVersion)
          _ -> Nothing
diff --git a/changelog.d/pkgconfig-once b/changelog.d/pkgconfig-once
new file mode 100644
index 00000000000..c3ac3ac47e0
--- /dev/null
+++ b/changelog.d/pkgconfig-once
@@ -0,0 +1,8 @@
+synopsis: PkgConfig individual calls
+prs: #9134
+
+description: {
+
+- `cabal` invokes `pkg-config` individually for each lib if querying for all doesn't return the expected result
+
+}

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 2/2] 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
+
+}