From b9f8e3b72ef20732317d30274b5ed0ebbf561cb7 Mon Sep 17 00:00:00 2001
From: Vadim Zeitlin <vadim@zeitlins.org>
Date: Fri, 23 Jan 2026 01:55:47 +0100
Subject: [PATCH] Fix MT use with libxml2 < 2.9.10 under Linux

libxml2 headers used to require _REENTRANT to be defined to actually
enable support for multiple threads and even though this was changed
back in cf68fe3d (Always define LIBXML_THREAD_ENABLED when enabled,
2019-02-27), still add -pthread to ensure _REENTRANT is defined just in
case we use an older version.
---
 src/CMakeLists.txt | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 059ac99..e378a2b 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -74,6 +74,20 @@ target_include_directories(xmlwrapp
     $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>
     $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
 )
+
+# Always use -pthread under Linux: this is required to ensure that _REENTRANT
+# is defined as libxml2 < 2.9.10 needs it to enable thread-safe operation.
+#
+# Note that using find_package(Threads) wouldn't work as it doesn't add any
+# compilation flags on modern Linux systems deeming them unnecessary (which
+# is formally correct but breaks using libxml2 in practice).
+if(CMAKE_SYSTEM_NAME STREQUAL "Linux")
+  target_compile_options(xmlwrapp
+    PRIVATE
+      -pthread
+  )
+endif()
+
 target_link_options(xmlwrapp
   PUBLIC
     ${LIBXML2_LDFLAGS}