Remove CMAKE_CXX_COMPILER and CMAKE_C_COMPILER for OSX

[henry0312]

#710

[henry0312]

we need to update Installation Guide like this:

git clone --recursive https://github.com/Microsoft/LightGBM ; cd LightGBM
mkdir build ; cd build
cmake -DCMAKE_CXX_COMPILER=/usr/local/bin/g++- -DCMAKE_C_COMPILER=/usr/local/bin/gcc ..
make -j4 

[guolinke]

This may broke the installation of python/R package, since it is hard to specific -DCMAKE_CXX_COMPILER=/usr/local/bin/g++- -DCMAKE_C_COMPILER=/usr/local/bin/gcc in their nested cmake command.

[guolinke]

BTW, can this cmake -DCMAKE_CXX_COMPILER=/usr/local/bin/g++- DCMAKE_C_COMPILER=/usr/local/bin/gcc
simplify to cmake -DCMAKE_CXX_COMPILER=g++7 -DCMAKE_C_COMPILER=gcc7 ?

[henry0312]

Currently, brew install gcc installs gcc-7, so -DCMAKE_CXX_COMPILER=g++-7 - -DCMAKE_C_COMPILER=gcc-7 is also ok until release of gcc-8.

[guolinke]

@henry0312
It that okay if just using cmake -DCMAKE_CXX_COMPILER=g++ -DCMAKE_C_COMPILER=gcc ?

[chivee]

I agreed that we should remove the line that specific the g++ in the cmake for Apple. but that means that we should also alter the travis test script as well. I have branched a branch for testing

[henry0312]

-DCMAKE_CXX_COMPILER=g++ and -DCMAKE_C_COMPILER=gcc may be not okay, because gcc and g++ are Clang, not GNU GCC in OSX.

~/.ghq/github.com/henry0312/LightGBM remove_apple_compiler*
❯ type gcc
gcc is /usr/bin/gcc

~/.ghq/github.com/henry0312/LightGBM remove_apple_compiler*
❯ gcc -v
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 8.1.0 (clang-802.0.42)
Target: x86_64-apple-darwin16.6.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

~/.ghq/github.com/henry0312/LightGBM remove_apple_compiler*
❯ type g++
g++ is /usr/bin/g++

~/.ghq/github.com/henry0312/LightGBM remove_apple_compiler*
❯ g++ -v
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 8.1.0 (clang-802.0.42)
Target: x86_64-apple-darwin16.6.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

[chivee]

@henry0312, @guolinke ,the problem that we are faced is that the apple linked the gcc and g++ to AppleClang, I have added the test for the mac, but which means that Apple users should manually specify their compiler.

[guolinke]

can following works ?

export CXX=g++-7
export CC=gcc-7
cmake  ..

if this can work, we can use it for the python/R build .

[chivee]

actually /usr/local/bin/g++ didn't exist if you are only install gcc using brew

[henry0312]

@guolinke This may work fine, I guess.

@chivee you're right. So we specify gcc-7, gcc-6 and so on.

[chivee]

I have checked that the minimum version that we need is gcc 4.8.3 and clang 3.8

[henry0312]

I don't know much about Travis.
Which gcc (GNU) are available in osx of Travis?

[chivee]

We have fully control of which version should be use in Travis.

[henry0312]

Then, I think exporting CXX and CC before tests in osx is fine for Travis.

[guolinke]

you can try to add following at this line:https://github.com/Microsoft/LightGBM/blob/master/.travis/test.sh#L16
updated:

if [[ $TRAVIS_OS_NAME == "osx" ]]; then
  export CXX=g++-7
  export CC=gcc-7
fi

[henry0312]

it this osx's tests script?

[guolinke]

@henry0312 it is the test for all systems.

[chivee]

@guolinke, we don't need to specific version in the travis, because that the osX version travis used didn't link gcc to AppleClang

[henry0312]

@chivee Is gcc and g++ GNU GCC in osx of Travis?

[chivee]

@henry0312 , Refer to a previous blog, I guess no, gcc still link to AppleClang

[henry0312]

GCC 4.8 (available as gcc-4.8, gcc is still Apple’s LLVM-gcc) (GitHub issue #2423)

This means gcc is LLVM-gcc....🤔

[chivee]

Yes, let's stay using 'g++-7'

[henry0312]

sorry, I don't understand #719 (comment).

Does "version" in your comment mean os type?

[henry0312]

Anyway, all tests in Travis are passed 🎉