From 53653350cd730208e82f40728a955c6f8c4d8846 Mon Sep 17 00:00:00 2001
From: Martijn Bastiaan <martijn@qbaylogic.com>
Date: Tue, 2 Aug 2022 15:49:27 +0200
Subject: [PATCH] Don't warn about 'prepositive-qualified-module' in Paths_pkgs

Enabling '-Wprepositive-qualified-module' in a project leads to warnings
when used in combination with Cabal's Paths_* feature. Given that this
is code outside of a user's control, this warning should be disabled
locally.
---
 .../Distribution/Simple/Build/PathsModule/Z.hs  |  8 ++++++++
 .../PathsModule/ImportQualifiedPost/Main.hs     |  4 ++++
 .../PathsModule/ImportQualifiedPost/my.cabal    | 17 +++++++++++++++++
 .../ImportQualifiedPost/setup.cabal.out         |  5 +++++
 .../PathsModule/ImportQualifiedPost/setup.out   |  5 +++++
 .../ImportQualifiedPost/setup.test.hs           |  4 ++++
 templates/Paths_pkg.template.hs                 |  5 +++++
 7 files changed, 48 insertions(+)
 create mode 100644 cabal-testsuite/PackageTests/PathsModule/ImportQualifiedPost/Main.hs
 create mode 100644 cabal-testsuite/PackageTests/PathsModule/ImportQualifiedPost/my.cabal
 create mode 100644 cabal-testsuite/PackageTests/PathsModule/ImportQualifiedPost/setup.cabal.out
 create mode 100644 cabal-testsuite/PackageTests/PathsModule/ImportQualifiedPost/setup.out
 create mode 100644 cabal-testsuite/PackageTests/PathsModule/ImportQualifiedPost/setup.test.hs

diff --git a/Cabal/src/Distribution/Simple/Build/PathsModule/Z.hs b/Cabal/src/Distribution/Simple/Build/PathsModule/Z.hs
index 6488ea06101..9100dc629ec 100644
--- a/Cabal/src/Distribution/Simple/Build/PathsModule/Z.hs
+++ b/Cabal/src/Distribution/Simple/Build/PathsModule/Z.hs
@@ -41,6 +41,14 @@ render z_root = execWriter $ do
     return ()
   else do
     return ()
+  if (zSupportsCpp z_root)
+  then do
+    tell "#if __GLASGOW_HASKELL__ >= 810\n"
+    tell "{-# OPTIONS_GHC -Wno-prepositive-qualified-module #-}\n"
+    tell "#endif\n"
+    return ()
+  else do
+    return ()
   tell "{-# OPTIONS_GHC -fno-warn-missing-import-lists #-}\n"
   tell "{-# OPTIONS_GHC -w #-}\n"
   tell "module Paths_"
diff --git a/cabal-testsuite/PackageTests/PathsModule/ImportQualifiedPost/Main.hs b/cabal-testsuite/PackageTests/PathsModule/ImportQualifiedPost/Main.hs
new file mode 100644
index 00000000000..d82a4bd93b7
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PathsModule/ImportQualifiedPost/Main.hs
@@ -0,0 +1,4 @@
+module Main where
+
+main :: IO ()
+main = return ()
diff --git a/cabal-testsuite/PackageTests/PathsModule/ImportQualifiedPost/my.cabal b/cabal-testsuite/PackageTests/PathsModule/ImportQualifiedPost/my.cabal
new file mode 100644
index 00000000000..8ad771ececd
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PathsModule/ImportQualifiedPost/my.cabal
@@ -0,0 +1,17 @@
+name: PathsModule
+version: 0.1
+license: BSD3
+author: Martijn Bastiaan
+category: PackageTests
+build-type: Simple
+Cabal-version: >= 1.2
+
+description:
+    Check that the generated paths module compiles.
+
+Executable TestPathsModule
+    main-is: Main.hs
+    if impl(ghc >= 8.10.0)
+        ghc-options: -Werror -fwarn-prepositive-qualified-module
+    other-modules: Paths_PathsModule
+    build-depends: base
diff --git a/cabal-testsuite/PackageTests/PathsModule/ImportQualifiedPost/setup.cabal.out b/cabal-testsuite/PackageTests/PathsModule/ImportQualifiedPost/setup.cabal.out
new file mode 100644
index 00000000000..bead24d62fd
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PathsModule/ImportQualifiedPost/setup.cabal.out
@@ -0,0 +1,5 @@
+# Setup configure
+Configuring PathsModule-0.1...
+# Setup build
+Preprocessing executable 'TestPathsModule' for PathsModule-0.1..
+Building executable 'TestPathsModule' for PathsModule-0.1..
diff --git a/cabal-testsuite/PackageTests/PathsModule/ImportQualifiedPost/setup.out b/cabal-testsuite/PackageTests/PathsModule/ImportQualifiedPost/setup.out
new file mode 100644
index 00000000000..bead24d62fd
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PathsModule/ImportQualifiedPost/setup.out
@@ -0,0 +1,5 @@
+# Setup configure
+Configuring PathsModule-0.1...
+# Setup build
+Preprocessing executable 'TestPathsModule' for PathsModule-0.1..
+Building executable 'TestPathsModule' for PathsModule-0.1..
diff --git a/cabal-testsuite/PackageTests/PathsModule/ImportQualifiedPost/setup.test.hs b/cabal-testsuite/PackageTests/PathsModule/ImportQualifiedPost/setup.test.hs
new file mode 100644
index 00000000000..ac477fa7567
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PathsModule/ImportQualifiedPost/setup.test.hs
@@ -0,0 +1,4 @@
+import Test.Cabal.Prelude
+-- Test that Paths module is generated and available for executables.
+main = setupAndCabalTest $ setup_build []
+
diff --git a/templates/Paths_pkg.template.hs b/templates/Paths_pkg.template.hs
index 6bc6b7875e6..8e1e03d27e4 100644
--- a/templates/Paths_pkg.template.hs
+++ b/templates/Paths_pkg.template.hs
@@ -7,6 +7,11 @@
 {% if not absolute %}
 {-# LANGUAGE ForeignFunctionInterface #-}
 {% endif %}
+{% if supportsCpp %}
+#if __GLASGOW_HASKELL__ >= 810
+{-# OPTIONS_GHC -Wno-prepositive-qualified-module #-}
+#endif
+{% endif %}
 {-# OPTIONS_GHC -fno-warn-missing-import-lists #-}
 {-# OPTIONS_GHC -w #-}
 module Paths_{{ manglePkgName packageName }} (