[service] Visual Studio 18 2026 Problems

[cuppajoeman]

What is your problem/feature request?

Microsoft has released Visual Studio 18 2026, so when you go to the downloads page you by default only see listings for the newest version:

https://visualstudio.microsoft.com/downloads/

The first minor inconvenience to those users will be that when running conan install . is that they won't match with any of the binaries in conan center because none of them use 195 which is the version that comes with the new install.

But after that, depending on which packages, used then they may run into an issue that's caused by the fact that the lowest version of cmake that supports the Visual Studio 18 2026 generator is cmake 4.2, which is a new version of cmake which has recently been released.

Specifically the issue arises in any package that has a tool requirement on cmake (any version) will currently fail when trying to be compiled, this is because the highest version of cmake available on conan center is 4.1.2, and it will fail because that version of cmake is less than version 4.2.0 and thus has no idea that Visual Studio 18 exists yet, and so when that package tries to get compiled it will fail out because no such generator exists (well that version thinks so).

Concretely this has already happened, in at least the following two packages that I work with daily:

• https://conan.io/center/recipes/assimp?version=6.0.2
• https://conan.io/center/recipes/opus?version=1.5.2

You will go through conan install . --build=missing and then suddenly be interrupted by a confusing cmake error, which you would then have to go version hunting to figure out why it occurred.

I'm sure there's a workaround where we tell new users to not download this new version of visual studio, but I think there will be an array of programmers who will install visual studio blindly from the site, then install the newest version of cmake, then get conan, go for a conan install . then go for a conan install . --build=missing and then run into this error saying that cmake has no idea that Visual Studio 18 exists, then get confused and either create an issue about this or simply just not be able to make progress with their packages.

---

Again, to replicate this error just get a freshly installed version of visual studio from the microsoft website, then install the newest version of cmake from their website, and install conan. Then make a new conan project that uses any package that has a tool requirement on cmake. Then try to conan install, you will encounter this problem.

---

The solution to this would be if we can bump the version of cmake up to 4.2 on conancenter. Packages like opus have a version requirement of this form:

conan-center-index/recipes/opus/all/conanfile.py

Line 37 in 82da3b0

self.tool_requires("cmake/[>=3.16 <5]")

Any packages that have a cmake requirement of this form will be fixed by this bump.

Other packages such as assimp will have a harder time:

conan-center-index/recipes/assimp/5.x/conanfile.py

Lines 213 to 215 in 82da3b0

	def build_requirements(self):
	if Version(self.version) >= "5.4.0":
	self.tool_requires("cmake/[>=3.22 <4]")

As their version number bounds will have to be modified.

[jcar87]

Thanks for reporting this!

the lowest version of cmake that supports the Visual Studio 18 2026 generator is cmake 4.2, which is a new version of cmake which has recently been released.

interestingly, it has not been released yet, https://cmake.org/download/ - it's currently a release candidate. Once it is published we will make it available in Conan Center.

Right now you have a couple of options, it should be fairly painless.

1. In your Conan profile, add the following to override the cmake dependency to use 4.2.0 unconditionally, regardless of what the recipe requires.
   The snippet below assumes it is installed at the system level (install the RC from https://cmake.org/download/ using the MSI installer).
   Once there's a release and it is published in Conan Center, the [platform_tool_requires] becomes unnecessary.

[replace_tool_requires]
cmake/*: cmake/4.2.0

[platform_tool_requires]
cmake/4.2.0

2. Or you can just default to using Ninja, then this will work with CMake 3.x

[conf]
tools.cmake.cmaketoolchain:generator=Ninja

(it needs to be discoverable in Path)

they won't match with any of the binaries in conan center because none of them use 195 which is the version that comes with the new install.

Since 195 is backwards compatible with all the 19x before it - you can reflect it in the compatibilty plugin such that Conan considers binaries built with 194 (you can read more about the compatibility extension here)

you would have to edit extensions\plugins\compatibility\compatibility.py in your Conan home directory (typically ~/.conan2)

If you look for the block that starts with # MSVC 194->193 fallback compatibility, you can tweak it such that when an exact match for 195 is not found, it considers binaries built with 194 too - it would look like this:

    # MSVC 194->193 fallback compatibility
    compiler = conanfile.settings.get_safe("compiler")
    compiler_version = conanfile.settings.get_safe("compiler.version")
    if compiler == "msvc":
        msvc_fallback = {"194": "193",
                         "195": "194"}.get(compiler_version)
        if msvc_fallback:
            factors.append([{"compiler.version": msvc_fallback}])

⚠️ you have to remove the first two lines in the file, otherwise the changes will be overwritten by Conan

# This file was generated by Conan. Remove this comment if you edit this file or Conan
# will destroy your changes.

With the compatibility fallback, conan install would look like this when it doesnt find a binary built with 195, but finds one with 194

======== Computing necessary packages ========
zlib/1.3.1: Main binary package 'b29b6622afb24e650905bb3f2e27034370730ade' missing
zlib/1.3.1: Checking 1 compatible configurations
zlib/1.3.1: Compatible configurations not found in cache, checking servers
zlib/1.3.1: 'bf083199c71b5d660bf9523713b0cd79bc0919fb': compiler.version=194
zlib/1.3.1: Found compatible package 'bf083199c71b5d660bf9523713b0cd79bc0919fb': compiler.version=194
Requirements
    zlib/1.3.1#b8bc2603263cf7eccbd6e17e66b0ed76:bf083199c71b5d660bf9523713b0cd79bc0919fb#353e623af6d53aa40b92ce44d4472247 - Download (conancenter2)

These should be safe to link in programs where other components are built with the new toolset, as long as the new toolset is doing the linking.
Hopefully this also saves you time - if your settings/options match the binaries available in Conan Center, you don't have to build them from source :)

[jcar87]

We're progressively removing the cmake upper bound constraint on most recipes (initially we assumed that CMake 4.x would be fully breaking - I dont think this was entirely off, given the long list of recipes that did break with 4.0 #26878 )

That will take time for us to deal with.

However, and based on intuition alone, I wouldn't be surprised if the CMake maintainers end up backporting the Visual Studio 2026 generator to the legacy 3.x release.