From c32b769b8cde4402cda7be5de11020f54a014946 Mon Sep 17 00:00:00 2001
From: Matthew Craven <clyring@gmail.com>
Date: Tue, 22 Oct 2024 17:04:02 -0400
Subject: [PATCH] Add a constraint reflecting #665 to the package description
 (#698)

Some combinations of Apple toolchains and GHC versions will
provide headers that anger -Werror=undef.  See discussion
at that #665.
---
 bytestring.cabal | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/bytestring.cabal b/bytestring.cabal
index 20cc13ea..c337c1ac 100644
--- a/bytestring.cabal
+++ b/bytestring.cabal
@@ -185,6 +185,13 @@ library
     if os(windows) && impl(ghc < 9.3)
       extra-libraries:  gcc
 
+  if arch(aarch64)
+    -- The libffi in Apple's darwin toolchain doesn't
+    -- play nice with -Wundef.  Recent GHCs work around this.
+    -- See also https://github.com/haskell/bytestring/issues/665
+    -- and https://gitlab.haskell.org/ghc/ghc/-/issues/23568
+    build-depends:    base (>= 4.17.2 && < 4.18) || >= 4.18.1
+
   include-dirs:      include
   install-includes:  fpstring.h
                      bytestring-cpp-macros.h