[API Compat] Not targeting .NET 8 framework in versions 8.*

[dosper7]

I am building a CI/CD pipeline using a .NET 8-based container image. In this pipeline, I have a validation step where I want to check for potential breaking changes and fail if any are detected. To my surprise, when I installed the Microsoft.DotNet.ApiCompat.Tool and tried to use it, it failed because it targets the .NET 6 framework, which I do not have installed.

apicompat --version
8.0.401+41b13414c4a35aac269719f7281cf74c9c9aae31

Installing the .NET 6 runtime makes the tool work (version 6.0.33):

    wget https://dot.net/v1/dotnet-install.sh -O dotnet-install.sh
    chmod +x dotnet-install.sh
    ./dotnet-install.sh --runtime dotnet --version 6.0.33

Question:

Why isn't there version parity between the API Compat tool version 8.* and its dependent framework?

When I check the API Compat tool version 8.0.4 on the NuGet Package Explorer, I see it has a dependency on .NET 6:

If I inspect a more recent version (e.g., .NET 9 RC), I notice it depends on the latest LTS version (.NET 8), whereas I was expecting it to depend on .NET 9:

I realize I might be missing something, but I would like to understand the rationale or reasons behind this discrepancy. Can you help?

[dotnet-policy-service]

@dotnet/area-infrastructure-libraries a new issue has been filed in the ApiCompat area, please triage

[KalleOlaviNiemitalo]

If I inspect a more recent version (e.g., .NET 9 RC), I notice it depends on the latest LTS version (.NET 8)

That's intentional in #38485

[dosper7]

If I inspect a more recent version (e.g., .NET 9 RC), I notice it depends on the latest LTS version (.NET 8)

That's intentional in #38485

That means that .NET 8 base containers can't run Api Compat without having the .NET 6 runtime installed?

[KalleOlaviNiemitalo]

Well my comment was only for the net9 rc version of the tool.

But IIRC an option was added to dotnet tool install to allow running any tool on a higher version of .NET Runtime than it targets (major version roll-forward). I don't remember whether that is in .NET SDK 8 or only in 9. Doesn't seem to be documented at https://learn.microsoft.com/en-us/dotnet/core/tools/dotnet-tool-install yet.

[KalleOlaviNiemitalo]

The dotnet tool install --allow-roll-forward feature was #37231 and it's in .NET SDK 8.0.300.

For older SDKs, you can use the DOTNET_ROLL_FORWARD environment variable.

[KalleOlaviNiemitalo]

As for why Microsoft.DotNet.ApiCompat.Tool 8.0.402 targets .NET 6, I don't know the official reason but I'd guess that they wanted to have some version of the tool runnable on .NET 6 LTS until that goes out of support; no 6.* version of the tool was published; the 7.* versions of the tool were built as part of .NET SDK 7 which is already out of support; so the responsibility falls to 8.* versions of the tool. They could have made it multitarget .NET 6 and .NET 8 though.