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c#.netnugetupgradeversioning

Should Nuget package versions match the .NET TargetFramework?

I've long assumed that when you upgrade the Target Framework of a .NET project, that all of the related System.* and Microsoft.* Nuget package references should also be updated to match, but Nuget package manager will happily let you skip ahead or roll way back in time.

With the recent cadence of major .NET releases, I guess I'm just challenging that assumption now.

For example, let's say I have some project that is targeting net6.0, I can choose basically any published version of the needed Nuget packages I want, including stuff with releases from 6.x, 7.x, 8.x and even older stuff if I really wanted.

For reasons I can only describe as "visually looks right", I've always just matched the latest-in-major-version package to the TargetFramework version of the project. Is this the right thing to do? If I can't take the .NET 8 (or 9) project upgrade for some reason, can I still use newer versions of the System.* & Microsoft.* Nuget packages or would that cause problems? Is there a technical reason why these things should match (or shouldn't)?

I couldn't find specific documentation on this topic, since it's kind of esoteric. The closest is the migration guides which state do the thing, but don't really specify the why. https://learn.microsoft.com/en-us/aspnet/core/migration/70-80?view=aspnetcore-8.0&tabs=visual-studio

Solution

  • The only thing that really matters is that the dependencies of each package that's part of .NET are met.

    Let's look at System.Configuration.ConfigurationManager's dependencies for version 8.0.0:

    The only thing that really matters is that the dependencies of each package that's part of .NET are met.

    Let's look at System.Configuration.ConfigurationManager's dependencies for version 8.0.0:

    .NETFramework 4.6.2

    • No dependencies.

    .NETStandard 2.0

    • System.Security.Cryptography.ProtectedData (>= 8.0.0)

    net6.0

    • System.Security.Cryptography.ProtectedData (>= 8.0.0)

    net7.0

    • System.Diagnostics.EventLog (>= 8.0.0)
    • System.Security.Cryptography.ProtectedData (>= 8.0.0)

    net8.0

    • System.Diagnostics.EventLog (>= 8.0.0)
    • System.Security.Cryptography.ProtectedData (>= 8.0.0)

    I believe when you update your target framework for a project Visual Studio (and possibly the NuGet CLI) will warn you that you have package references that are targeting a different framework version. That's letting you know that you might get errors if you run the code without updating your packages.

    I can discern a few pieces of information from the dependencies of this package:

    1. There is no upper version limit for any of these dependencies. That means that this package should be compatible with all future versions of these dependencies. That's a bold claim on Microsoft's part, but they do control all of them so it's achievable.
    2. If you updated your target framework, did not update this package, but did update one of its dependencies you'd be fine due to point 1.
    3. If the dependency you updated in point 2 had a shared dependency with this package, let's say the ProtectedData package depends on EventLog as well starting at .NET 7, and you didn't have EventLog yet because your project was originall .NET 6, the update of ProtectedData would bring in the appropriate version of EventLog. In this case no conflicts will occur since the ConfigurationManager package doesn't use EventLog at that version.
    4. Taking point 3 but starting at version 7 instead of 6, yes there would be an existing dependency on EventLog >= 7.0.0, but since it's proclaimed to be compatible with any later version if another package updates it to 8.0 due to its own minimum dependency there will still be no conflict.
    5. Lastly, this dependency list is also showing target framework compatibility. The fact that it lists Framework 4.6.2 and shows no dependencies means it's compatible with 4.6.2 and anything that 4.6.2 is forward compatible to. .NET Standard 2.0 covers all of .NET Core (and I believe .NET 5? Not 100% on that.)

    So really you don't necessarily NEED to update the packages to make sure they work in a new target framework, but it's a good idea to to be 100% sure. And really the migration guidelines are only listing a couple of packages that are part of .NET overall so my guess is that Microsoft calls them out specifically because of compatibility issues between newer frameworks and older packages.