Fix gain-map detection with system libheif

CMakeLists.txt

@@ -761,6 +761,37 @@ if(UHDR_BUILD_TESTS)
         -P "${TESTS_DIR}/windows_unicode_cli_test.cmake"
     )
   endif()
+
+  # The fixture configures with the host compiler; skip target toolchains such as Android.
+  if(NOT CMAKE_CROSSCOMPILING)
+    set(_libheif_discovery_cmake_args -G "${CMAKE_GENERATOR}")
+    if(CMAKE_GENERATOR_PLATFORM)
+      list(APPEND _libheif_discovery_cmake_args -A "${CMAKE_GENERATOR_PLATFORM}")
+    endif()
+    if(CMAKE_GENERATOR_TOOLSET)
+      list(APPEND _libheif_discovery_cmake_args -T "${CMAKE_GENERATOR_TOOLSET}")
+    endif()
+
+    foreach(_variable IN ITEMS CMAKE_CXX_COMPILER CMAKE_TOOLCHAIN_FILE
+        CMAKE_OSX_ARCHITECTURES CMAKE_OSX_DEPLOYMENT_TARGET CMAKE_OSX_SYSROOT)
+      if(DEFINED ${_variable} AND NOT "${${_variable}}" STREQUAL "")
+        string(REPLACE ";" "\\;" _value "${${_variable}}")
+        list(APPEND _libheif_discovery_cmake_args "-D${_variable}=${_value}")
+      endif()
+    endforeach()
+
+    foreach(_case IN ITEMS no-defs empty-defs one-def multiple-defs missing-api)
+      add_test(
+        NAME "LibheifDiscovery-${_case}"
+        COMMAND ${CMAKE_COMMAND}
+          ${_libheif_discovery_cmake_args}
+          -S "${TESTS_DIR}/cmake/libheif-discovery"
+          -B "${CMAKE_CURRENT_BINARY_DIR}/libheif-discovery/${_case}"
+          "-DLIBHEIF_MODULE_DIR=${CMAKE_CURRENT_SOURCE_DIR}/cmake"
+          "-DLIBHEIF_TEST_CASE=${_case}"
+      )
+    endforeach()
+  endif()
 endif()
 
 if(UHDR_BUILD_BENCHMARK)

cmake/Findlibheif.cmake

@@ -91,7 +91,7 @@ if(LIBHEIF_TARGET)
     list(APPEND CMAKE_REQUIRED_INCLUDES ${LIBHEIF_INCLUDE_DIR})
   endif()
   if(LIBHEIF_DEFS)
-    set(CMAKE_REQUIRED_DEFINITIONS "-D${LIBHEIF_DEFS}")
+    list(TRANSFORM LIBHEIF_DEFS PREPEND "-D" OUTPUT_VARIABLE CMAKE_REQUIRED_DEFINITIONS)
   endif()
 
   # Perform a compile-only check to avoid linking transitive dependencies

tests/cmake/libheif-discovery/CMakeLists.txt

@@ -0,0 +1,57 @@
+cmake_minimum_required(VERSION 3.15)
+project(libheif_discovery_regression LANGUAGES CXX)
+
+if(NOT LIBHEIF_MODULE_DIR OR NOT LIBHEIF_TEST_CASE)
+  message(FATAL_ERROR "LIBHEIF_MODULE_DIR and LIBHEIF_TEST_CASE are required")
+endif()
+
+set(_fixture_root "${CMAKE_CURRENT_BINARY_DIR}/fixture")
+set(_package_dir "${_fixture_root}/lib/cmake/libheif")
+file(MAKE_DIRECTORY "${_package_dir}")
+
+set(_include_dir "${_fixture_root}/include/${LIBHEIF_TEST_CASE}/libheif")
+file(MAKE_DIRECTORY "${_include_dir}")
+if(LIBHEIF_TEST_CASE STREQUAL "one-def")
+  file(WRITE "${_include_dir}/heif.h" [=[
+#ifdef LIBHEIF_TEST_SINGLE
+int heif_image_handle_get_gain_map_image_handle();
+#endif
+]=])
+elseif(LIBHEIF_TEST_CASE STREQUAL "multiple-defs")
+  file(WRITE "${_include_dir}/heif.h" [=[
+#if defined(LIBHEIF_TEST_FIRST) && defined(LIBHEIF_TEST_SECOND)
+int heif_image_handle_get_gain_map_image_handle();
+#endif
+]=])
+elseif(LIBHEIF_TEST_CASE STREQUAL "missing-api")
+  file(WRITE "${_include_dir}/heif.h" "/* Gain map API intentionally absent. */\n")
+else()
+  file(WRITE "${_include_dir}/heif.h" "int heif_image_handle_get_gain_map_image_handle();\n")
+endif()
+
+file(WRITE "${_package_dir}/libheifConfig.cmake" [=[
+add_library(libheif::heif INTERFACE IMPORTED)
+set_property(TARGET libheif::heif PROPERTY INTERFACE_INCLUDE_DIRECTORIES "${LIBHEIF_TEST_INCLUDE_DIR}")
+if(LIBHEIF_TEST_CASE STREQUAL "empty-defs")
+  set_property(TARGET libheif::heif PROPERTY INTERFACE_COMPILE_DEFINITIONS "")
+elseif(LIBHEIF_TEST_CASE STREQUAL "one-def")
+  set_property(TARGET libheif::heif PROPERTY INTERFACE_COMPILE_DEFINITIONS LIBHEIF_TEST_SINGLE)
+elseif(LIBHEIF_TEST_CASE STREQUAL "multiple-defs" OR LIBHEIF_TEST_CASE STREQUAL "missing-api")
+  set_property(TARGET libheif::heif PROPERTY INTERFACE_COMPILE_DEFINITIONS
+    LIBHEIF_TEST_FIRST LIBHEIF_TEST_SECOND)
+endif()
+]=])
+
+set(libheif_DIR "${_package_dir}")
+set(LIBHEIF_TEST_INCLUDE_DIR "${_fixture_root}/include/${LIBHEIF_TEST_CASE}")
+list(APPEND CMAKE_MODULE_PATH "${LIBHEIF_MODULE_DIR}")
+unset(LIBHEIF_HAS_GAIN_MAP CACHE)
+find_package(libheif REQUIRED MODULE)
+
+if(LIBHEIF_TEST_CASE STREQUAL "missing-api")
+  if(LIBHEIF_HAS_GAIN_MAP)
+    message(FATAL_ERROR "The feature check accepted a missing gain map API")
+  endif()
+elseif(NOT LIBHEIF_HAS_GAIN_MAP)
+  message(FATAL_ERROR "The feature check rejected the ${LIBHEIF_TEST_CASE} fixture")
+endif()