GH-144679: When building with VS2026 on Windows, use PlatformToolSet v145 by default

[chris-eibl]

Furthermore do not warn when PlatformToolSet v145 is used.

• Issue: When building with VS2026 on Windows, use PlatformToolSet v145 by default #144679

[chris-eibl]

On main, shall we warn for older toolsets like v141 or v142 now?

Likewise, shall we keep a warning for v145 on 3.13 / 3.14?

[Wulian233]

The minimum VS version for building Python now is 2017.
https://docs.python.org/3.15/using/configure.html

I removed the support for 2015 a year ago #124103 . However, according to the Mainstream End Date of the VS lifecycle, currently only VS2022 is still supported

https://learn.microsoft.com/lifecycle/products/visual-studio-2019

[zooba]

Yeah, let's start warning for those older ones.

[chris-eibl]

The minimum VS version for building Python now is 2017.
https://docs.python.org/3.15/using/configure.html

Maybe we should change that to 2022 since we emit a warning for the older ones now?

[zooba]

It's not required though, whereas I'm pretty sure we made changes that prevent using the compilers that came with VS 2015. If you want to write something that's clearer about the "works with" toolset version, the "released/supported with" toolset versions, and the VS versions that typically include these toolsets (newer VS should have older MSVC available as options, but not selected by default), feel free.

[chris-eibl]

Ah, got it now, thanks for the explanation. So no need to change that from my point of view, until in the future we do a change that requires a newer version than VS 2017.

[zooba]

Approved with change in comments (ping me if nobody else merges)

[chris-eibl]

I did not yet touch

cpython/Tools/msi/bundle/bootstrap/pythonba.vcxproj

Lines 24 to 25 in 46d5106

	<PlatformToolset Condition="'$(PlatformToolset)' == '' and '$(VisualStudioVersion)' == '17.0'">v143</PlatformToolset>
	<PlatformToolset Condition="'$(PlatformToolset)' == '' and '$(VisualStudioVersion)' == '16.0'">v142</PlatformToolset>

since this seems to be related to the deprecated msi installers. But adding v145 here would be no harm?

[zooba]

But adding v145 here would be no harm?

Uh, it might be. I think we need to match the versions supported by WiX, which probably don't extend to v145. Try it - it should run in CI when you touch the file - but be prepared to change it to use v143.

[chris-eibl]

Ok, let's try. In case it fails when switching CI to windows-2025-vs2026, I'll revert back ...

[zooba]

FYI, this is the line that matters:

https://github.com/python/cpython/actions/runs/21963900630/job/63448457298?pr=144680#step:3:5827

C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.44.35207\bin\HostX86\x86\link.exe /ERRORREPORT:QUEUE /OUT:"D:\a\cpython\cpython\PCbuild\obj\315win32_Release\msi_pythonba\PythonBA.dll" /NOLOGO /LIBPATH:"D:\a\cpython\cpython\externals\windows-installer\wix-314\sdk\vs2017\lib\x86" comctl32.lib gdiplus.lib msimg32.lib shlwapi.lib wininet.lib dutil.lib balutil.lib version.lib uxtheme.lib kernel32.lib user32.lib gdi32.lib winspool.lib comdlg32.lib advapi32.lib shell32.lib ole32.lib oleaut32.lib uuid.lib odbc32.lib odbccp32.lib /DEF:"pythonba.def" /MANIFEST /MANIFESTUAC:"level='asInvoker' uiAccess='false'" /manifest:embed /DEBUG:FULL /PDB:"D:\a\cpython\cpython\PCbuild\obj\315win32_Release\msi_pythonba\PythonBA.pdb" /TLBID:1 /DYNAMICBASE /NXCOMPAT /IMPLIB:"D:\a\cpython\cpython\PCbuild\obj\315win32_Release\msi_pythonba\PythonBA.lib" /MACHINE:X86 /SAFESEH /DLL D:\a\cpython\cpython\PCbuild\obj\315win32_Release\msi_pythonba\PythonBootstrapperApplication.obj

Most critical, the MSVC version (14.44.35207 here) and the libpath ("D:\a\cpython\cpython\externals\\windows-installer\wix-314\sdk\vs2017\lib\x86" here). That path will contain a static library, which has to match the compiler version. Apparently this one does, despite being labelled vs2017, so I'm not actually sure what magic is going on here - possibly the compiler team figured out a way to make them forward compatible?