Revert "Do not enforce a specific C++ standard"
This reverts commit d839b77928b3f9bebbbd18a1095ea2af890f3c34.
Reason for revert: Breaks the BUILD on macOS
Change-Id: I49f448ed4942cc88df9e4ad3b78d56f6be04351d
diff --git a/CMakeLists.txt b/CMakeLists.txt
index fa110a9..69432f7 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -29,14 +29,47 @@
# Authors: keir@google.com (Keir Mierle)
# alexs.mac@gmail.com (Alex Stewart)
-cmake_minimum_required(VERSION 3.10)
-
-if (POLICY CMP0074) # Added in CMake 3.12
+cmake_minimum_required(VERSION 3.5)
+cmake_policy(VERSION 3.5)
+if (POLICY CMP0074)
# FindTBB.cmake uses TBB_ROOT in a way that is historical, but also compliant
# with CMP0074 so suppress the legacy compatibility warning and allow its use.
cmake_policy(SET CMP0074 NEW)
endif()
+# Set the C++ version when compiling Ceres.
+#
+# Reflect a user-specified (via -D) CMAKE_CXX_STANDARD if present, otherwise
+# default to C++14.
+set(DEFAULT_CXX_STANDARD ${CMAKE_CXX_STANDARD})
+if (NOT DEFAULT_CXX_STANDARD)
+ set(DEFAULT_CXX_STANDARD 14)
+endif()
+set(CMAKE_CXX_STANDARD ${DEFAULT_CXX_STANDARD} CACHE STRING
+ "C++ standard (minimum 14)" FORCE)
+# Restrict CMAKE_CXX_STANDARD to the valid versions permitted and ensure that
+# if one was forced via -D that it is in the valid set.
+set(ALLOWED_CXX_STANDARDS 14 17 20)
+set_property(CACHE CMAKE_CXX_STANDARD PROPERTY STRINGS ${ALLOWED_CXX_STANDARDS})
+list(FIND ALLOWED_CXX_STANDARDS ${CMAKE_CXX_STANDARD} POSITION)
+if (POSITION LESS 0)
+ message(FATAL_ERROR "Invalid CMAKE_CXX_STANDARD: ${CMAKE_CXX_STANDARD}. "
+ "Must be one of: ${ALLOWED_CXX_STANDARDS}")
+endif()
+# Specify the standard as a hard requirement, otherwise CMAKE_CXX_STANDARD is
+# interpreted as a suggestion that can decay *back* to lower versions.
+set(CMAKE_CXX_STANDARD_REQUIRED ON CACHE BOOL "")
+mark_as_advanced(CMAKE_CXX_STANDARD_REQUIRED)
+
+# MSVC versions < 2015 did not fully support >= C++14, and technically even
+# 2015 did not support a couple of smaller features
+if (CMAKE_CXX_COMPILER_ID MATCHES MSVC AND
+ CMAKE_CXX_COMPILER_VERSION VERSION_LESS 14.0)
+ message(FATAL_ERROR "Invalid CMAKE_CXX_COMPILER_VERSION: "
+ "${CMAKE_CXX_COMPILER_VERSION}. Ceres requires at least MSVC 2015 for "
+ "C++14 support.")
+endif()
+
# On macOS, add the Homebrew prefix (with appropriate suffixes) to the
# respective HINTS directories (after any user-specified locations). This
# handles Homebrew installations into non-standard locations (not /usr/local).
@@ -204,6 +237,7 @@
endif (IOS)
unset(CERES_COMPILE_OPTIONS)
+message("-- Building with C++${CMAKE_CXX_STANDARD}")
# Eigen.
# Eigen delivers Eigen3Config.cmake since v3.3.3
@@ -457,7 +491,6 @@
mark_as_advanced(benchmark_DIR)
endif()
-# TODO Report features using the FeatureSummary CMake module
if (BUILD_SHARED_LIBS)
message("-- Building Ceres as a shared library.")
else (BUILD_SHARED_LIBS)
diff --git a/internal/ceres/CMakeLists.txt b/internal/ceres/CMakeLists.txt
index 5606804..f57c2e8 100644
--- a/internal/ceres/CMakeLists.txt
+++ b/internal/ceres/CMakeLists.txt
@@ -314,10 +314,17 @@
target_compile_options(ceres_internal PUBLIC $<TARGET_PROPERTY:ceres,COMPILE_OPTIONS>)
target_compile_definitions(ceres_internal PRIVATE ceres_EXPORTS)
-# Ensure the minimum required C++ language version is fulfilled as our
-# requirement by downstream clients. Consumers can choose the same or a newer
-# language standard revision.
-target_compile_features(ceres PUBLIC cxx_std_14)
+# The ability to specify a minimum language version via cxx_std_[11,14,17]
+# requires CMake >= 3.8. Prior to that we have to specify the compiler features
+# we require.
+if (CMAKE_VERSION VERSION_LESS 3.8)
+ set(REQUIRED_PUBLIC_CXX_FEATURES cxx_alignas cxx_alignof cxx_constexpr)
+else()
+ # Forward whatever C++ version Ceres was compiled with as our requirement
+ # for downstream clients.
+ set(REQUIRED_PUBLIC_CXX_FEATURES cxx_std_${CMAKE_CXX_STANDARD})
+endif()
+target_compile_features(ceres PUBLIC ${REQUIRED_PUBLIC_CXX_FEATURES})
set_target_properties(ceres PROPERTIES
VERSION ${CERES_VERSION}
