SCons build with development gcc8

Question

I'm attempting to build MongoDB v4.0 on CentOS7 (https://github.com/mongodb/mongo/wiki/Build-Mongodb-From-Source), and am unfamiliar with the python toolset included for building. The toolset requires gcc8.2 or newer, which I have installed with devtoolset-8-gcc and devtoolset-8-g++. I enable the toolset using scl enable devtoolset-8 bash And execute the scons build following the build guide, however scons appears to build its own environment which doesnt include the library at /opt/rh/devtoolset-8/.

[user@localhost mongo.git]$ sudo scl enable devtoolset-8 bash
[sudo] password for user:
[root@localhost mongo.git]# gcc --version
gcc (GCC) 8.2.1 20180905 (Red Hat 8.2.1-3)
Copyright (C) 2018 Free Software Foundation, Inc.
...
[root@localhost mongo.git]# ./buildscripts/scons.py
scons: Reading SConscript files ...
scons version: 2.5.0
python version: 2 7 5 'final' 0
...
Checking if C compiler is GCC 8.2 or newer...no
Checking if C++ compiler is GCC 8.2 or newer...no
ERROR: Refusing to build with compiler that does not meet requirements
See /opt/mongodb/mongo.git/build/scons/config.log for details

The log file contents are available at https://pastebin.com/jB2q4NxN.

My attempts to modify the python script to include the path per the scons manual have netted another error:

[root@localhost mongo.git]# buildscripts/scons.py all
Traceback (most recent call last):
  File "buildscripts/scons.py", line 7, in <module>
    env = Environment(ENV = {'PATH' : os.environ['PATH']})
NameError: name 'Environment' is not defined

After I added the lines

import os
env = Environment(ENV = {'PATH' : os.environ['PATH']})

To my buildscripts/scons.py file. Am I adding this in the wrong place perhaps? Why is the environment variable not available?

Thanks.

Answer 1

Just name the path to the compiler with the CC and CXX Variables on the SCons command line:

scons CC=/path/to/toolset/gcc CXX=/path/to/toolset/g++

Please note however, that GCC 8 is not officially supported for building MongoDB 4.0. You may find that it doesn't build, or that it builds with warnings that are promoted to errors. You can work around some of them by adding the flag --disable-warnings-as-errors to your SCons invocation.

The reason you don't see the environment variables in your build is that SCons by default ignores the users environment in the interest of producing reproducible builds. If you really want to let SCons see the current shell environment, you can add --variables-files=etc/scons/propagate_shell_environment.vars to your SCons invocation.