Obsolete error message when MS Visual C++ Build Tools missing

Environment

• pip version: 20.2.1
• Python version: 3.8.3
• OS: Windows 10 (fully patched, on latest release)

Description

When installing a module that needs Microsoft’s Visual C++ Build Tools, and these tools are not present, this message is displayed: error: Microsoft Visual C++ 14.0 is required. Get it with "Microsoft Visual C++ Build Tools": https://visualstudio.microsoft.com/downloads/

This message is erroneous for a few reasons:

• There is no such product at https://visualstudio.microsoft.com/downloads/. I think https://visualstudio.microsoft.com/visual-cpp-build-tools/ is the correct URL.
• Version 14 probably not required. It may be a minimum requirement, not absolute. That should be validated before updating the language.
• People who already have Visual Studio installed probably should modify their installation instead of downloading build tools. The warning message doesn’t say that. If you install build tools along with Visual Studio, you may run into issues.

In my case, I no longer got this error after adding C++ support to my Visual Studio 2017 installation per the link above. That validates that:

1. the build tools can be installed as a component of Visual Studio instead of separately
2. version 14 is not strictly required (Visual Studio 2017 = version 15.9.25)

Expected behavior

Error message wording should be accurate and not encourage undesirable choices.

How to Reproduce

Install a package that needs to be compiled with C++. For example: python -m pip install wordcloud

Output

The output ends with this:

error: Microsoft Visual C++ 14.0 is required. Get it with "Microsoft Visual C++ Build Tools": https://visualstudio.microsoft.com/downloads/

[jaraco]

Feel free to send a PR. The code is here.

[BoarGules]

The remark “version 14 is not strictly required” is quite untrue in practice.

Method MSVCCompiler.query_vcvarsall() determines if there is a compiler installed by searching for the file vcvarsall.bat, which exists in 14.2. Failing that, it then recommends the user download Visual C++ 14.2, which is no longer readily available. It can be downloaded, but only if you have a paid subscription. The link in the error message points to https://visualstudio.microsoft.com/downloads/ which does indeed work, but the only compiler available free from that page is Visual Studio 2019 (a.k.a. version 16). That compiler does not satisfy the query_vcvarsall() test because the counterpart of vcvarsall.bat in 16.0 is VsDevCmd.bat.

In fact even if you have VC++ 14.2, distutils still gets things wrong, presumably holdovers from earlier versions of VC++. First one must work out the correct values for environment variables LIBPATH and INCLUDE. After that, to make a compile work using the command lines that distutils issues, it is also necessary to copy the contents of C:\Program Files (x86)\Windows Kits\10\Lib\10.0.10240.0\ucrt\x64 and C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\lib\amd64 to a new folder Pythonxx\PCBuild\amd64 which distutils puts as a LIBPATH parameter to link.exe but which does not actually exist. Likewise it is necessary to copy C:\Program Files (x86)\Windows Kits\10\bin\x64\rc.exe to an existing folder C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\bin\amd64 because distutils knows the executable is there but Microsoft reckons otherwise.

All of this probably a doddle if you are a seasoned MSC programmer, but (I speak from experience) painful to someone who switched from C to Python around the time when Visual C 3 came out. And quite out of reach for a Python beginner who gets this message from PIP when he tries to install numpy. That happened today.

So it is not just the message that is obsolete: the whole of distutils.msvc9compiler needs attention paid not just to what it says but to what it does. It is of course entitled to insist on one and only one MS compiler to do what it does, but it must be one that is readily available, and the command lines it issues should work on a vanilla installation of that compiler, without the user having to modify the folder layout to put files where distutils expects them to be.