Creating Xcode project from Cmake contains unwanted compiler flags - c++

Question

I've been unable to find a definitive answer, so apologies if the answer is out there.
I use cmake to generate project files as I tend to work cross-platform. On OSX/Xcode, I'm seeing unwanted compiler flags being used, specifically warning enable/disable. I like to compile with as many warnings on as possible, and set warnings as errors.
Consider the following:
File: CMakeLists.txt
cmake_minimum_required( VERSION 3.0 )
project( test )
set( CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS} -std=c++14 )
add_compile_options( "-Werror" )
add_compile_options( "-Weverything" )
add_compile_options( "-Wno-c++98-compat-pedantic" )
add_compile_options( "-Wno-padded" )
add_executable( Test main.cpp )
target_link_libraries( Test libstdc++.dylib libc++.dylib )
File: main.cpp
#include <iostream>
int main( int argc, char * const argv[] )
{
(void)argc;
(void)argv;
std::cout << "Kittens." << std::endl;
return 0;
}
If I then run cmake:
cmake -G Xcode .
(normally I'd use a builds directory, but not here for simplicity).
Then build (from the command line):
cmake --build . --config Debug --target ALL_BUILD
The simple sample will compile. If I now look at the command used to compile main.cpp I see the following:
CompileC test.build/Debug/Test.build/Objects-normal/x86_64/main.o main.cpp normal x86_64 c++ com.apple.compilers.llvm.clang.1_0.compiler
cd /Users/username/Development/test
export LANG=en_US.US-ASCII
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang -x c++ -arch x86_64 -fmessage-length=101 -fdiagnostics-show-note-include-stack -fmacro-backtrace-limit=0 -fcolor-diagnostics -Wno-trigraphs -fpascal-strings -O0 -Wno-missing-field-initializers -Wno-missing-prototypes -Wno-return-type -Wno-non-virtual-dtor -Wno-overloaded-virtual -Wno-exit-time-destructors -Wno-missing-braces -Wparentheses -Wswitch -Wno-unused-function -Wno-unused-label -Wno-unused-parameter -Wno-unused-variable -Wunused-value -Wno-empty-body -Wno-uninitialized -Wno-unknown-pragmas -Wno-shadow -Wno-four-char-constants -Wno-conversion -Wno-constant-conversion -Wno-int-conversion -Wno-bool-conversion -Wno-enum-conversion -Wno-shorten-64-to-32 -Wno-newline-eof -Wno-c++11-extensions -DCMAKE_INTDIR=\"Debug\" -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.11.sdk -fasm-blocks -fstrict-aliasing -Wdeprecated-declarations -Winvalid-offsetof -mmacosx-version-min=10.11 -g -Wno-sign-conversion -I/Users/username/Development/test/Debug/include -I/Users/username/Development/test/test.build/Debug/Test.build/DerivedSources/x86_64 -I/Users/username/Development/test/test.build/Debug/Test.build/DerivedSources -Wmost -Wno-four-char-constants -Wno-unknown-pragmas -F/Users/username/Development/test/Debug -std=c++14 -Werror -Weverything -Wno-c++98-compat-pedantic -Wno-padded -MMD -MT dependencies -MF /Users/username/Development/test/test.build/Debug/Test.build/Objects-normal/x86_64/main.d --serialize-diagnostics /Users/username/Development/test/test.build/Debug/Test.build/Objects-normal/x86_64/main.dia -c /Users/username/Development/test/main.cpp -o /Users/username/Development/test/test.build/Debug/Test.build/Objects-normal/x86_64/main.o
The really annoying thing here is any of the -W options.
In my CMakeLists.txt I've clearly said I want all warnings, warnings treated as errors, and whitelisted a couple of warnings.
However, if I strip out all the -W options in the compile command, I see (in addition to what I asked for):
-Wno-trigraphs
-Wno-missing-field-initializers
-Wno-missing-prototypes
-Wno-return-type
-Wno-non-virtual-dtor
-Wno-overloaded-virtual
-Wno-exit-time-destructors
-Wno-missing-braces
-Wparentheses
-Wswitch
-Wno-unused-function
-Wno-unused-label
-Wno-unused-parameter
-Wno-unused-variable
-Wunused-value
-Wno-empty-body
-Wno-uninitialized
-Wno-unknown-pragmas
-Wno-shadow
-Wno-four-char-constants
-Wno-conversion
-Wno-constant-conversion
-Wno-int-conversion
-Wno-bool-conversion
-Wno-enum-conversion
-Wno-shorten-64-to-32
-Wno-newline-eof
-Wno-c++11-extensions
-Winvalid-offsetof
-Wno-sign-conversion
-Wmost
-Wno-four-char-constants
-Wno-unknown-pragmas
Some of those things listed I really do not want disabled. I really want just the -W options I specified in the cmake file being used for compilation, but I can't see who is injecting all these extra things and from where.
Is there any way I can get cmake to tell xcode not to include all these extra -W options from compilation?
Note: using:
cmake 3.5.2
Apple LLVM version 7.3.0 (clang-703.0.31)

Answer 1

At project() call, CMake detects compiler (you may see corresponded messages when cmake is executed) and sets default flags for it. These flags are stored in variables CMAKE_CXX_FLAGS (common) and CMAKE_CXX_FLAGS_<CONFIG> (configuration-specific).
You may modify these variables as you want:
1) completely rewrite them
set(CMAKE_CXX_FLAGS "<desired-value>")
2) append new flags to them
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} <additional-flags>")
3) remove specific values from them
string(REPLACE "<unwanted-flag>" "" CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})
# or
string(REGEX REPLACE "<unwanted-flag-regex>" "" CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})
and so on.