Clean up CMake version checks

cmake/OpenCVCompilerOptions.cmake

@@ -377,7 +377,7 @@ if(NOT OPENCV_SKIP_LINK_AS_NEEDED)
   if(UNIX)
     set(_option "-Wl,--as-needed")
     set(_saved_CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS}")
-    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} ${_option}")  # requires CMake 3.2+ and CMP0056
+    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} ${_option}")
     ocv_check_compiler_flag(CXX "" HAVE_LINK_AS_NEEDED)
     set(CMAKE_EXE_LINKER_FLAGS "${_saved_CMAKE_EXE_LINKER_FLAGS}")
     if(HAVE_LINK_AS_NEEDED)
@@ -393,7 +393,7 @@ if(NOT OPENCV_SKIP_LINK_NO_UNDEFINED)
   if(UNIX AND (NOT CMAKE_SYSTEM_NAME MATCHES "OpenBSD"))
     set(_option "-Wl,--no-undefined")
     set(_saved_CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS}")
-    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} ${_option}")  # requires CMake 3.2+ and CMP0056
+    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} ${_option}")
     ocv_check_compiler_flag(CXX "" HAVE_LINK_NO_UNDEFINED)
     set(CMAKE_EXE_LINKER_FLAGS "${_saved_CMAKE_EXE_LINKER_FLAGS}")
     if(HAVE_LINK_NO_UNDEFINED)

cmake/OpenCVUtils.cmake

@@ -1944,9 +1944,6 @@ macro(ocv_get_smart_file_name output_var fpath)
   unset(__subir)
 endmacro()
 
-# Needed by install(DIRECTORY ...)
-set(compatible_MESSAGE_NEVER MESSAGE_NEVER)
-
 macro(ocv_git_describe var_name path)
   if(GIT_FOUND)
     execute_process(COMMAND "${GIT_EXECUTABLE}" describe --tags --exact-match --dirty

cmake/templates/OpenCVConfig.cmake.in

@@ -54,8 +54,7 @@ SET(OpenCV_VERSION_STATUS "@OPENCV_VERSION_STATUS@")
 
 include(FindPackageHandleStandardArgs)
 
-if(NOT CMAKE_VERSION VERSION_LESS 2.8.8
-    AND OpenCV_FIND_COMPONENTS  # prevent excessive output
+if(OpenCV_FIND_COMPONENTS  # prevent excessive output
 )
   # HANDLE_COMPONENTS was introduced in CMake 2.8.8
   list(APPEND _OpenCV_FPHSA_ARGS HANDLE_COMPONENTS)
@@ -67,13 +66,6 @@ else()
   set(_OpenCV_HANDLE_COMPONENTS_MANUALLY TRUE)
 endif()
 
-# Extract directory name from full path of the file currently being processed.
-# Note that CMake 2.8.3 introduced CMAKE_CURRENT_LIST_DIR. We reimplement it
-# for older versions of CMake to support these as well.
-if(CMAKE_VERSION VERSION_LESS "2.8.3")
-  get_filename_component(CMAKE_CURRENT_LIST_DIR "${CMAKE_CURRENT_LIST_FILE}" PATH)
-endif()
-
 # Extract the directory where *this* file has been installed (determined at cmake run-time)
 # Get the absolute path with no ../.. relative marks, to eliminate implicit linker warnings
 get_filename_component(OpenCV_CONFIG_PATH "${CMAKE_CURRENT_LIST_DIR}" REALPATH)
@@ -128,19 +120,15 @@ if(NOT TARGET opencv_core)
   include(${CMAKE_CURRENT_LIST_DIR}/OpenCVModules${OpenCV_MODULES_SUFFIX}.cmake)
 endif()
 
-if(NOT CMAKE_VERSION VERSION_LESS "2.8.11")
-  # Target property INTERFACE_INCLUDE_DIRECTORIES available since 2.8.11:
-  # * http://www.cmake.org/cmake/help/v2.8.11/cmake.html#prop_tgt:INTERFACE_INCLUDE_DIRECTORIES
-  foreach(__component ${OpenCV_LIB_COMPONENTS})
-    if(TARGET ${__component})
-      set_target_properties(
-          ${__component}
-          PROPERTIES
-          INTERFACE_INCLUDE_DIRECTORIES "${OpenCV_INCLUDE_DIRS}"
-      )
-    endif()
-  endforeach()
-endif()
+foreach(__component ${OpenCV_LIB_COMPONENTS})
+  if(TARGET ${__component})
+    set_target_properties(
+        ${__component}
+        PROPERTIES
+        INTERFACE_INCLUDE_DIRECTORIES "${OpenCV_INCLUDE_DIRS}"
+    )
+  endif()
+endforeach()
 
 
 if(NOT DEFINED OPENCV_MAP_IMPORTED_CONFIG)
@@ -275,31 +263,23 @@ endif()
 # ==============================================================
 set(OpenCV_LIBRARIES ${OpenCV_LIBS})
 
-# Require C++11 features for OpenCV modules
-if(CMAKE_VERSION VERSION_LESS "3.1")
-  if(NOT OpenCV_FIND_QUIETLY AND NOT OPENCV_HIDE_WARNING_COMPILE_FEATURES)
-    message(STATUS "OpenCV: CMake version is low (${CMAKE_VERSION}, required 3.1+). Can't enable C++11 features: https://github.com/opencv/opencv/issues/13000")
-  endif()
-else()
-  set(__target opencv_core)
-  if(TARGET opencv_world)
-    set(__target opencv_world)
-  endif()
-  set(__compile_features cxx_std_11)  # CMake 3.8+
-  if(DEFINED OPENCV_COMPILE_FEATURES)
-    set(__compile_features ${OPENCV_COMPILE_FEATURES})  # custom override
-  elseif(CMAKE_VERSION VERSION_LESS "3.8")
-    set(__compile_features cxx_auto_type cxx_rvalue_references cxx_lambdas)
-  endif()
-  if(__compile_features)
-    # Simulate exported result of target_compile_features(opencv_core PUBLIC ...)
-    set_target_properties(${__target} PROPERTIES
-        INTERFACE_COMPILE_FEATURES "${__compile_features}"
-    )
-  endif()
-  unset(__target)
-  unset(__compile_features)
+# Require C++17 features for OpenCV modules
+set(__target opencv_core)
+if(TARGET opencv_world)
+  set(__target opencv_world)
 endif()
+set(__compile_features cxx_std_17)
+if(DEFINED OPENCV_COMPILE_FEATURES)
+  set(__compile_features ${OPENCV_COMPILE_FEATURES})  # custom override
+endif()
+if(__compile_features)
+  # Simulate exported result of target_compile_features(opencv_core PUBLIC ...)
+  set_target_properties(${__target} PROPERTIES
+      INTERFACE_COMPILE_FEATURES "${__compile_features}"
+  )
+endif()
+unset(__target)
+unset(__compile_features)
 
 #
 # Some macros for samples

cmake/templates/OpenCVConfig.root-ANDROID.cmake.in

@@ -28,13 +28,6 @@
 #
 # ===================================================================================
 
-# Extract directory name from full path of the file currently being processed.
-# Note that CMake 2.8.3 introduced CMAKE_CURRENT_LIST_DIR. We reimplement it
-# for older versions of CMake to support these as well.
-if(CMAKE_VERSION VERSION_LESS "2.8.3")
-  get_filename_component(CMAKE_CURRENT_LIST_DIR "${CMAKE_CURRENT_LIST_FILE}" PATH)
-endif()
-
 if(NOT DEFINED OpenCV_CONFIG_SUBDIR)
   set(OpenCV_CONFIG_SUBDIR "/abi-${ANDROID_NDK_ABI_NAME}")
 endif()

cmake/templates/OpenCVConfig.root-WIN32.cmake.in

@@ -34,11 +34,9 @@
 #      - OpenCV_STATIC
 #      - OpenCV_CUDA
 
-if(CMAKE_VERSION VERSION_GREATER 2.6)
-  get_property(OpenCV_LANGUAGES GLOBAL PROPERTY ENABLED_LANGUAGES)
-  if(NOT ";${OpenCV_LANGUAGES};" MATCHES ";CXX;")
-    enable_language(CXX)
-  endif()
+get_property(OpenCV_LANGUAGES GLOBAL PROPERTY ENABLED_LANGUAGES)
+if(NOT ";${OpenCV_LANGUAGES};" MATCHES ";CXX;")
+  enable_language(CXX)
 endif()
 
 if(NOT DEFINED OpenCV_STATIC)

doc/CMakeLists.txt

@@ -309,6 +309,6 @@ if(DOXYGEN_FOUND)
   install(DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/doxygen/html
     DESTINATION "${OPENCV_DOC_INSTALL_PATH}"
     COMPONENT "docs" OPTIONAL
-    ${compatible_MESSAGE_NEVER}
+    MESSAGE_NEVER
   )
 endif()

modules/java/jar/CMakeLists.txt

@@ -101,7 +101,7 @@ if(BUILD_DOCS)
     install(DIRECTORY ${OpenCV_BINARY_DIR}/doc/doxygen/html/javadoc
       DESTINATION "${OPENCV_DOC_INSTALL_PATH}/html"
       COMPONENT "docs" OPTIONAL
-      ${compatible_MESSAGE_NEVER}
+      MESSAGE_NEVER
     )
   elseif(OPENCV_JAVA_SDK_BUILD_TYPE STREQUAL "JAVA")
     set(Java_JAVADOC_EXECUTABLE ${Java_JAVADOC_EXECUTABLE} -encoding utf-8)
@@ -121,7 +121,7 @@ if(BUILD_DOCS)
     install(DIRECTORY ${OpenCV_BINARY_DIR}/doc/doxygen/html/javadoc/${the_module}/
       DESTINATION "${OPENCV_DOC_INSTALL_PATH}/html/javadoc"
       COMPONENT "docs" OPTIONAL
-      ${compatible_MESSAGE_NEVER}
+      MESSAGE_NEVER
     )
   else()
     ocv_assert(0)

samples/sycl/CMakeLists.txt

@@ -1,6 +1,7 @@
 if(OPENCV_SKIP_SAMPLES_SYCL)
   return()
 endif()
+cmake_minimum_required(VERSION 3.13)
 
 ocv_install_example_src(sycl *.cpp *.hpp CMakeLists.txt)