Use non-version checked add_compile_options

Commit aebc7fa added version checks for CMake compatibility. In reality,
only the add_compile_definitions need the check - add_compile_options
itself has been supported since 3.0. Tested and confirmed built
successfully with CMake 3.8.0.

Author: mrjoel

CMakeLists.txt

@@ -95,23 +95,11 @@ macro(use_compilation_warning_as_error)
     if(MSVC)
         # Only enabled in debug because some old versions of VS STL generate
         # warnings when compiled in release configuration.
-        if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.12.0)
-            add_compile_options($<$<CONFIG:Debug>:/WX>)
-        else()
-            set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} /WX ")
-        endif()
+        add_compile_options($<$<CONFIG:Debug>:/WX>)
     elseif(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
-        if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.12.0)
-            add_compile_options(-Werror)
-        else()
-            set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Werror")
-        endif()
+        add_compile_options(-Werror)
         if(JSONCPP_WITH_STRICT_ISO)
-            if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.12.0)
-                add_compile_options(-pedantic-errors)
-            else()
-                set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -pedantic-errors")
-            endif()
+            add_compile_options(-pedantic-errors)
         endif()
     endif()
 endmacro()
@@ -122,57 +110,29 @@ include_directories(${jsoncpp_SOURCE_DIR}/include)
 if(MSVC)
     # Only enabled in debug because some old versions of VS STL generate
     # unreachable code warning when compiled in release configuration.
-    if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.12.0)
-        add_compile_options($<$<CONFIG:Debug>:/W4>)
-    else()
-        set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} /W4 ")
-    endif()
+    add_compile_options($<$<CONFIG:Debug>:/W4>)
 endif()
 
 if(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
     # using regular Clang or AppleClang
-    if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.12.0)
-        add_compile_options(-Wall -Wconversion -Wshadow -Werror=conversion -Werror=sign-compare)
-    else()
-        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wconversion -Wshadow -Werror=conversion -Werror=sign-compare")
-    endif()
+    add_compile_options(-Wall -Wconversion -Wshadow -Werror=conversion -Werror=sign-compare)
 elseif(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
     # using GCC
-    if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.12.0)
-        add_compile_options(-Wall -Wconversion -Wshadow -Wextra)
-    else()
-        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wconversion -Wshadow -Wextra")
-    endif()
+    add_compile_options(-Wall -Wconversion -Wshadow -Wextra)
     # not yet ready for -Wsign-conversion
 
     if(JSONCPP_WITH_STRICT_ISO)
-        if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.12.0)
-            add_compile_options(-Wpedantic)
-        else()
-            set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wpedantic")
-        endif()
+        add_compile_options(-Wpedantic)
     endif()
     if(JSONCPP_WITH_WARNING_AS_ERROR)
-        if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.12.0)
-            add_compile_options(-Werror=conversion)
-        else()
-            set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Werror=conversion")
-        endif()
+        add_compile_options(-Werror=conversion)
     endif()
 elseif(CMAKE_CXX_COMPILER_ID STREQUAL "Intel")
     # using Intel compiler
-    if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.12.0)
-        add_compile_options(-Wall -Wconversion -Wshadow -Wextra -Werror=conversion)
-    else()
-        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wconversion -Wshadow -Wextra -Werror=conversion")
-    endif()
+    add_compile_options(-Wall -Wconversion -Wshadow -Wextra -Werror=conversion)
 
     if(JSONCPP_WITH_STRICT_ISO AND NOT JSONCPP_WITH_WARNING_AS_ERROR)
-        if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.12.0)
-            add_compile_options(-Wpedantic)
-        else()
-            set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wpedantic")
-        endif()
+        add_compile_options(-Wpedantic)
     endif()
 endif()
 

example/CMakeLists.txt

@@ -10,7 +10,7 @@ set(EXAMPLES
 add_definitions(-D_GLIBCXX_USE_CXX11_ABI)
 
 if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU" OR CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra ")
+    add_compile_options(-Wall -Wextra)
 elseif(CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
     add_definitions(
         -D_SCL_SECURE_NO_WARNINGS

src/lib_json/CMakeLists.txt

@@ -6,7 +6,7 @@ if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
 
     #-Werror=* was introduced -after- GCC 4.1.2
     if(GNUCXX_VERSION VERSION_GREATER 4.1.2)
-        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Werror=strict-aliasing")
+        add_compile_options("-Werror=strict-aliasing")
     endif()
 endif()