Introduce a Standard `$(TargetFrameworkVersionMajor)` MSBuild Property

[ActivistInvestor]

Summary

I propose adding a new, standard MSBuild property, $(TargetFrameworkVersionMajor), that returns only the major version number of the currently targeted framework. This would greatly simplify conditional logic within .props and .targets files in multi-targeted projects, particularly for users moving to the new SDK-style project format.

Background and Motivation

In modern .NET multi-targeting projects, the primary property most-commonly used in conditional build logic is $(TargetFramework) (e.g., net48, net6.0, net8.0, net9.0-windows, etc.). When writing conditional logic, users often need to distinguish between major framework generations only (e.g., to load different reference assemblies, set specific compiler flags, or define environment variables).

Currently, this requires using verbose, repetitive MSBuild string functions in many locations:

<PropertyGroup Condition="$([System.String]::new('$(TargetFramework)').StartsWith('net4'))">
    <FrameworkMajorVer>4</FrameworkMajorVer>
</PropertyGroup>
<PropertyGroup Condition="$([System.String]::new('$(TargetFramework)').StartsWith('net8'))">
    <FrameworkMajorVer>8</FrameworkMajorVer>
</PropertyGroup>

<Target Name="ValidateRefs" BeforeTargets="PrepareForBuild">
    <Error Condition="'$(FrameworkMajorVer)' == '8' And '$(REF_PATH_NET8)' == ''"
           Text="Reference path for .NET 8 is not set." />
</Target>

Proposed Feature

Introduce a single, read-only property:

$(TargetFrameworkVersionMajor)

$(TargetFramework) Value	Proposed $(TargetFrameworkVersionMajor) Value
net462	4
net48	4
net6.0	6
net8.0	8
net8.0-windows	8
net9.0	9
net10.0	10

Benefits

✅ Readability: Simplifies complex conditional logic, e.g.,

Condition="'$(TargetFrameworkVersionMajor)' == '8'"
Condition="'$(TargetFrameworkVersionMajor)' >= '6'"

✅ Maintainability: Reduces the need for redundant string functions or custom property definitions across numerous build files.

✅ Consistency: Simplifies conditional logic that only cares about the major framework version, allowing conditional testing to see different variants of the same major framework version (e.g., net10.0, net10.0-windows, etc.) as equivalent, thereby standardizing a common pattern currently implemented manually by developers.

This small addition would be a significant quality-of-life improvement for anyone maintaining complex multi-targeted codebases.

[KalleOlaviNiemitalo]

Only checking the version seems like it would do the wrong thing for targeting .NET Standard.

There's already the TargetFrameworkVersion property.

There's also the [MSBuild]::IsTargetFrameworkCompatible property function https://learn.microsoft.com/visualstudio/msbuild/property-functions#msbuild-targetframework-and-targetplatform-functions but AFAIK it does not support custom aliases (https://learn.microsoft.com/dotnet/core/tools/sdk-errors/netsdk1013, NuGet/Home#5154).

[ActivistInvestor]

Only checking the version seems like it would do the wrong thing for targeting .NET Standard.

That's probably true. My use cases focus mainly on .NET Framework (4.x) and NETCoreApp (6+), and in fact, the only valid TFMs for this use case are 'net4xx', 'net8.0[-windows]', 'net9.0[-windows]' and 'net10.0[-windows]'. I'm not sure if different flavors of NET are even equatable in terms of versions because it's highly-inconsistent.

So, in the more generic case, I think a comparison would requires more than just a version or major version.

Also, it would be immensely useful if every framework flavor/version had a consistent, equatable unique identifier that could be used in MSBuild, rather than having to deal with the type/flavor and the version. I'm still not entirely sure what 'compatible' means WRT IsTargetFrameworkCompatible().