From 6b1a6958c4b4a7a2824b3cc0c125758e26bd380f Mon Sep 17 00:00:00 2001
From: Matt Clarkson <mattyclarkson@gmail.com>
Date: Fri, 1 Aug 2014 14:24:56 +0100
Subject: [PATCH] CMake function for adding compiler flags

---
 CMakeLists.txt                 | 34 ++++++++---------------------
 cmake/AddCXXCompilerFlag.cmake | 39 ++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 25 deletions(-)
 create mode 100644 cmake/AddCXXCompilerFlag.cmake

diff --git a/CMakeLists.txt b/CMakeLists.txt
index c1ad616f..ade38436 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -20,10 +20,8 @@ include_directories(${source_dir}/include)
 ExternalProject_Get_Property(googletest binary_dir)
 link_directories(${binary_dir})
 
-# Set up the compiler flags
-include(CheckCXXCompilerFlag)
-
 # Enable the latest C++ standard possible
+include(CheckCXXCompilerFlag)
 check_cxx_compiler_flag(--std=c++14 HAVE_FLAG_CXX_14)
 check_cxx_compiler_flag(--std=c++11 HAVE_FLAG_CXX_11)
 check_cxx_compiler_flag(--std=c++0x HAVE_FLAG_CXX_0X)
@@ -36,32 +34,18 @@ elseif (HAVE_FLAG_CXX_0X)
 endif()
 
 # Turn compiler warnings up to 11
-check_cxx_compiler_flag(-Wall HAVE_FLAG_WALL)
-if (HAVE_FLAG_WALL)
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall")
-endif()
-check_cxx_compiler_flag(-Wshadow HAVE_FLAG_WSHADOW)
-if (HAVE_FLAG_WSHADOW)
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wshadow")
-endif()
-check_cxx_compiler_flag(-Werror HAVE_FLAG_WERROR)
-if (HAVE_FLAG_WERROR)
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Werror")
-endif()
-check_cxx_compiler_flag(-pedantic-errors HAVE_FLAG_PEDANTIC_ERRORS)
-if (HAVE_FLAG_PEDANTIC_ERRORS)
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -pedantic-errors")
-endif()
+include(AddCXXCompilerFlag)
+add_cxx_compiler_flag(-Wall)
+add_cxx_compiler_flag(-Wshadow)
+add_cxx_compiler_flag(-Werror)
+add_cxx_compiler_flag(-pedantic-errors)
+
+# Release flags
+add_cxx_compiler_flag(-fno-strict-aliasing RELEASE)
 
 # Add a debug definition so we can make decisions in the compilation
 set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} -DDEBUG")
 
-# We relax the aliasing in release
-check_cxx_compiler_flag(-fno-strict-aliasing HAVE_FLAG_NO_STRICT_ALIASING)
-if (HAVE_FLAG_NO_STRICT_ALIASING)
-  set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -fno-strict-aliasing")
-endif()
-
 # Set OS
 if(${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
 	add_definitions(-DOS_MACOSX)
diff --git a/cmake/AddCXXCompilerFlag.cmake b/cmake/AddCXXCompilerFlag.cmake
new file mode 100644
index 00000000..d4a2de05
--- /dev/null
+++ b/cmake/AddCXXCompilerFlag.cmake
@@ -0,0 +1,39 @@
+# - Adds a compiler FLAG if it is supported by the compiler
+#
+# This function checks that the supplied compiler FLAG is supported and then
+# adds it to the corresponding compiler FLAGs
+#
+#  add_cxx_compiler_FLAG(<FLAG> [<VARIANT>])
+#
+# - Example
+#
+# include(AddCXXCompilerFlag)
+# add_cxx_compiler_FLAG(-Wall)
+# add_cxx_compiler_FLAG(-no-strict-aliasing RELEASE)
+# Requires CMake 2.6+
+
+if(__add_cxx_compiler_FLAG)
+  return()
+endif()
+set(__add_cxx_compiler_FLAG INCLUDED)
+
+include(CheckCXXCompilerFlag)
+
+function(add_cxx_compiler_flag FLAG)
+  if(ARGV1)
+    set(VARIANT ${ARGV1})
+    string(TOLOWER ${VARIANT} VARIANT)
+    set(VARIANT " ${VARIANT}")
+  endif()
+  message("-- Check compiler${VARIANT} flag ${FLAG}")
+  string(TOUPPER ${FLAG} SANITIZED_FLAG)
+  string(REGEX REPLACE "[^A-Za-z_0-9]" "_" ${SANITIZED_FLAG} SANITIZED_FLAG)
+  check_cxx_compiler_flag(${FLAG} ${SANITIZED_FLAG})
+  if(${SANITIZED_FLAG})
+    message("-- Check compiler${VARIANT} flag ${FLAG} -- works")
+    string(REGEX REPLACE "[^A-Za-z_0-9]" "_" "${VARIANT}" VARIANT)
+    string(TOUPPER "${VARIANT}" VARIANT)
+    set(CMAKE_CXX_FLAGS${VARIANT} "${CMAKE_CXX_FLAGS}${VARIANT} ${FLAG}" PARENT_SCOPE)
+  endif()
+endfunction()
+