From a79a3c10ac89db14a18552ee33bdf9577692953e Mon Sep 17 00:00:00 2001
From: Juan Miguel Carceller <jmcarcell@users.noreply.github.com>
Date: Mon, 9 Feb 2026 13:54:10 +0100
Subject: [PATCH] Add support for Unity builds

---
 CMakeLists.txt                        | 9 +++++++++
 src/cpp/CMakeLists.txt                | 3 +++
 src/cpp/include/UTIL/LCStdHepRdrNew.h | 6 +++---
 3 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 4f81422d7..ccd8fb7d6 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -180,6 +180,15 @@ IF( NOT SIO_FOUND )
 
   FetchContent_MakeAvailable(sio_extern)
 
+  # Unity builds break the bundled zlib used by SIO because several of zlib's
+  # internal headers are intentionally unguarded and assume a single translation
+  # unit per source file.
+  foreach(_lcio_no_unity_tgt IN ITEMS ZLIB zlib zlibstatic zlibshared)
+    if(TARGET ${_lcio_no_unity_tgt})
+      set_property(TARGET ${_lcio_no_unity_tgt} PROPERTY UNITY_BUILD OFF)
+    endif()
+  endforeach()
+
   get_target_property(SIO_VERSION SIO::sio VERSION)
   get_target_property(SIO_INCLUDE_DIRS SIO::sio INCLUDE_DIRECTORIES)
 ENDIF()
diff --git a/src/cpp/CMakeLists.txt b/src/cpp/CMakeLists.txt
index f6733d237..6c304cb38 100644
--- a/src/cpp/CMakeLists.txt
+++ b/src/cpp/CMakeLists.txt
@@ -375,6 +375,9 @@ IF( BUILD_ROOTDICT )
     INCLUDE_DIRECTORIES( SYSTEM "${ROOT_INCLUDE_DIRS}" )
 
     ADD_SHARED_LIBRARY( lcioDict ${lcio_rootdict_sources} )
+    # ROOT dictionaries generate multiple translation units with many identical
+    # helper symbol names
+    set_property(TARGET lcioDict PROPERTY UNITY_BUILD OFF)
     TARGET_LINK_LIBRARIES( lcioDict ${ROOT_LIBRARIES} LCIO::lcio SIO::sio)
 
     IF( APPLE )
diff --git a/src/cpp/include/UTIL/LCStdHepRdrNew.h b/src/cpp/include/UTIL/LCStdHepRdrNew.h
index 16b1afa21..5d217d7ba 100644
--- a/src/cpp/include/UTIL/LCStdHepRdrNew.h
+++ b/src/cpp/include/UTIL/LCStdHepRdrNew.h
@@ -1,5 +1,5 @@
-#ifndef UTIL_LCStdHepRdr_H
-#define UTIL_LCStdHepRdr_H 1
+#ifndef UTIL_LCStdHepRdrNew_H
+#define UTIL_LCStdHepRdrNew_H 1
 
 #include "IMPL/LCCollectionVec.h"
 #include "UTIL/lStdHep.hh"
@@ -89,4 +89,4 @@ namespace UTIL{
 
 } // namespace UTIL
 
-#endif /* ifndef UTIL_LCStdHepRdr_H */
+#endif /* ifndef UTIL_LCStdHepRdrNew_H */