From 01c1b341a881ba49d538acdf29d49ca7fd8ada57 Mon Sep 17 00:00:00 2001
From: Alexander Alekhin <alexander.alekhin@intel.com>
Date: Mon, 3 Feb 2020 15:38:08 +0300
Subject: [PATCH] cmake: enable C++11 implicitly

---
 cmake/templates/OpenCVConfig.cmake.in         | 26 +++++++++++++++++++
 samples/CMakeLists.example.in                 |  5 ----
 samples/CMakeLists.txt                        |  4 ---
 .../android/face-detection/jni/CMakeLists.txt |  4 ---
 .../jni/CMakeLists.txt                        |  4 ---
 .../tutorial-4-opencl/jni/CMakeLists.txt      |  4 ---
 samples/cpp/example_cmake/CMakeLists.txt      |  4 ---
 7 files changed, 26 insertions(+), 25 deletions(-)

diff --git a/cmake/templates/OpenCVConfig.cmake.in b/cmake/templates/OpenCVConfig.cmake.in
index ef299a4515..2e9022a355 100644
--- a/cmake/templates/OpenCVConfig.cmake.in
+++ b/cmake/templates/OpenCVConfig.cmake.in
@@ -273,6 +273,32 @@ 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 "${__compile_features}"
+    )
+  endif()
+  unset(__target)
+  unset(__compile_features)
+endif()
+
 #
 # Some macros for samples
 #
diff --git a/samples/CMakeLists.example.in b/samples/CMakeLists.example.in
index 9a00ac2991..7cf20d5e44 100644
--- a/samples/CMakeLists.example.in
+++ b/samples/CMakeLists.example.in
@@ -12,11 +12,6 @@ file(TO_CMAKE_PATH "${EXAMPLE_FILE}" EXAMPLE_FILE)
 message(STATUS "Project: ${EXAMPLE_NAME}")
 message(STATUS "File   : ${EXAMPLE_FILE}")
 
-# Enable C++11
-set(CMAKE_CXX_STANDARD 11)
-set(CMAKE_CXX_STANDARD_REQUIRED TRUE)
-
-
 # Define project name
 project(${EXAMPLE_NAME})
 
diff --git a/samples/CMakeLists.txt b/samples/CMakeLists.txt
index 6e739a178e..1bbd3fc328 100644
--- a/samples/CMakeLists.txt
+++ b/samples/CMakeLists.txt
@@ -58,10 +58,6 @@ else()
 #===================================================================================================
 cmake_minimum_required(VERSION 3.1)
 
-# Enable C++11
-set(CMAKE_CXX_STANDARD 11)
-set(CMAKE_CXX_STANDARD_REQUIRED TRUE)
-
 project(samples C CXX)
 option(BUILD_EXAMPLES "Build samples" ON)
 
diff --git a/samples/android/face-detection/jni/CMakeLists.txt b/samples/android/face-detection/jni/CMakeLists.txt
index d395999ce0..15f8f4db38 100644
--- a/samples/android/face-detection/jni/CMakeLists.txt
+++ b/samples/android/face-detection/jni/CMakeLists.txt
@@ -1,9 +1,5 @@
 cmake_minimum_required(VERSION 3.6)
 
-# Enable C++11
-set(CMAKE_CXX_STANDARD 11)
-set(CMAKE_CXX_STANDARD_REQUIRED TRUE)
-
 set(target detection_based_tracker)
 project(${target} CXX)
 
diff --git a/samples/android/tutorial-2-mixedprocessing/jni/CMakeLists.txt b/samples/android/tutorial-2-mixedprocessing/jni/CMakeLists.txt
index 2219121fde..5b34f8b948 100644
--- a/samples/android/tutorial-2-mixedprocessing/jni/CMakeLists.txt
+++ b/samples/android/tutorial-2-mixedprocessing/jni/CMakeLists.txt
@@ -1,9 +1,5 @@
 cmake_minimum_required(VERSION 3.6)
 
-# Enable C++11
-set(CMAKE_CXX_STANDARD 11)
-set(CMAKE_CXX_STANDARD_REQUIRED TRUE)
-
 set(target mixed_sample)
 project(${target} CXX)
 
diff --git a/samples/android/tutorial-4-opencl/jni/CMakeLists.txt b/samples/android/tutorial-4-opencl/jni/CMakeLists.txt
index 6b3f3a0940..4fdea1356e 100644
--- a/samples/android/tutorial-4-opencl/jni/CMakeLists.txt
+++ b/samples/android/tutorial-4-opencl/jni/CMakeLists.txt
@@ -1,9 +1,5 @@
 cmake_minimum_required(VERSION 3.6)
 
-# Enable C++11
-set(CMAKE_CXX_STANDARD 11)
-set(CMAKE_CXX_STANDARD_REQUIRED TRUE)
-
 set(target mixed_sample)
 project(${target} CXX)
 
diff --git a/samples/cpp/example_cmake/CMakeLists.txt b/samples/cpp/example_cmake/CMakeLists.txt
index d3d86eed9d..8d5cd98af2 100644
--- a/samples/cpp/example_cmake/CMakeLists.txt
+++ b/samples/cpp/example_cmake/CMakeLists.txt
@@ -1,10 +1,6 @@
 # cmake needs this line
 cmake_minimum_required(VERSION 3.1)
 
-# Enable C++11
-set(CMAKE_CXX_STANDARD 11)
-set(CMAKE_CXX_STANDARD_REQUIRED TRUE)
-
 # Define project name
 project(opencv_example_project)