From cf5cfe39891f1dbd4c9d5d1d8e29ed3d2cdd6f44 Mon Sep 17 00:00:00 2001
From: Dichen Zhang <dichenzhang@google.com>
Date: Fri, 18 Sep 2026 22:21:01 +0000
Subject: [PATCH] cmake: prefer selected libheif headers and avoid system
 include demotion

- Prepend libheif include directories (from target interface or LIBHEIF_INCLUDE_DIRS) to PRIVATE_INCLUDE_DIR so they are searched before other dependency or system include paths.
- For CMake 3.25+, set SYSTEM FALSE on target libheif::heif to prevent it from being classified as a system target, ensuring its headers take precedence over conflicting host headers without stripping system include classification from other dependencies (e.g. GTest, Threads).
- Resolve ALIASED_TARGET before calling set_target_properties to prevent CMake configuration fatal errors when libheif::heif is an ALIAS target (e.g. from Findlibheif.cmake aliasing 'heif' or 'PkgConfig::PC_LIBHEIF').
- Fall back to LIBHEIF_INCLUDE_DIRS if the target does not define INTERFACE_INCLUDE_DIRECTORIES.
- Guard get_target_property with if(TARGET libheif::heif) to prevent CMake configuration errors when using custom or legacy Find modules.

Ref: PR #468, PR #478
---
 CMakeLists.txt | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 16928b74..ad2b2736 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -646,6 +646,25 @@ if(UHDR_ENABLE_HEIF)
   endif()
   if(LIBHEIF_FOUND)
     message(STATUS "Found libheif: ${LIBHEIF_LIBRARIES}")
+    if(TARGET libheif::heif)
+      get_target_property(_heif_interface_dirs libheif::heif INTERFACE_INCLUDE_DIRECTORIES)
+      if(_heif_interface_dirs)
+        list(PREPEND PRIVATE_INCLUDE_DIR ${_heif_interface_dirs})
+      elseif(LIBHEIF_INCLUDE_DIRS)
+        list(PREPEND PRIVATE_INCLUDE_DIR ${LIBHEIF_INCLUDE_DIRS})
+      endif()
+      # CMake 3.25+: prevent libheif from being classified as a system target so
+      # its headers are prioritized over any conflicting host/system headers,
+      # without stripping system include classification from other dependencies.
+      # Resolve ALIASED_TARGET if libheif::heif is an ALIAS (e.g. from Findlibheif.cmake).
+      get_target_property(_heif_real_target libheif::heif ALIASED_TARGET)
+      if(NOT _heif_real_target)
+        set(_heif_real_target libheif::heif)
+      endif()
+      set_target_properties(${_heif_real_target} PROPERTIES SYSTEM FALSE)
+    elseif(LIBHEIF_INCLUDE_DIRS)
+      list(PREPEND PRIVATE_INCLUDE_DIR ${LIBHEIF_INCLUDE_DIRS})
+    endif()
     add_compile_options(-DUHDR_ENABLE_HEIF)
     list(APPEND PRIVATE_LINK_LIBS libheif::heif)
   else()