I need to build a dependency that uses SCons, and I need to build it with VC++2017, because another dependency I have cannot be built with VC++2019.
SCons successfully detects VC++2019 (v14.2), but not VC++2017 (v14.1):
c:\Python27\Scripts\scons [...] --msvc-version=14.1 [...]
scons: Reading SConscript files ...
scons version: 3.1.1
python version: 2 7 13 'final' 0
scons: warning: VC version 14.1 not installed. C/C++ compilers are most likely not set correctly.
Installed versions are: ['14.2', '14.0', '11.0']
[...]
C++ compiler $CC does not work
I have installed Visual Studio 2019 Enterprise as well as Visual Studio 2019 Build Tools, and for both, I have installed the platform tools / compiler for v14.1 and x86/x64. Compiling with the VC++2017 platform tools works fine in Visual Studio 2019 as well as using MSBuild, so the problem seems to be with SCons only.
How does SCons detect VC++2017 and VC++2019 and where should I start looking for the problem?
(There are old threads about this, but most of them are about people wondering why the "classic" detection/config methods using registry and vcvars.bat no longer work, so these are not helpful)
Update: This is still (2021-09-16) an issue, and a simple workaround may be this answer - My answer also has a workaround, but it is more complicated and mostly for educational purposes on how recent versions of VC++ compilers can be detected and are (not properly) detected by SCons. You may also want to use my workaround if you are creating a build script for a build server or multiple development machines with varying setups.
Update: The issue in SCons is still (2023-10-23) open and still being discussed. It might still affect newer versions of both Visual Studio and the platform toolset.
The current version of SCons does not support selecting MSVC v14.1 (aka "Visual C++ 2017") if Visual Studio 2019 is installed, but Visual Studio 2017 is not. I confirmed this by looking at the code of SCons (see below).
An alternative approach is to use the --msvc-script option instead of --msvc-version.
In the MSVC installation folder, typically c:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Auxiliary\Build\, you will find a file called vcvarsall.bat. If you run this without arguments, you will see that you can give it arguments for target platform and tools version, e.g.,
vcvarsall.bat x86 10.0.17763.0 -vcvars_ver=14.1
to compile for x86 (32-bit), Windows SDK version 10.0.17763.0 and tools version 14.1 (Visual C++ 2017).
Once you have found a command line for vcvarsall.bat that suits you, put it into a new BAT file that you create, say myvcconfig.bat (You have to use the complete path to vcvarsall.bat), then use the following command-line switch to SCons: --msvc-script=myvcconfig.bat.
*** Notes ***
Some parameters to SCons are redundant and will not work with --msvc-script, for example --32. SCons will tell you about them, so just remove them from the command-line.
The installation path of Visual Studio may be different from the one I provided above. You can find the installation path using Microsoft's own VSWhere tool. See also Locate Visual Studio
Visual Studio 2019 and Visual Studio Build Tools 2019 are separate installations with separate build tools. You can detect and use the vcvarsall.bat files of either ones. For example, if you are setting up a toolchain for a build server, you may want to use Visual Studio Build Tools 2019. If you just want to build one library one time (as in my case), just use the Visual Studio that is installed on your dev machine.
In case you are interested in how SCons detects MSVC and why it doesn't work, you can look at the source code in SCons/Tool/MSCommon/vc.py. You can clone the SCons GIT repository.
UPDATE: The following comment in vc.py (as of 2021-09-16) shows why this is still an issue in SCons and why this workaround is needed if you have both VC2017 and VC2019 compilers installed:
# make sure the cl.exe exists meaning the tool is installed
if ver_num > 14:
# 2017 and newer allowed multiple versions of the VC toolset to be
# installed at the same time. This changes the layout.
# Just get the default tool version for now
#TODO: support setting a specific minor VC version
Direct link (valid at time of writing)