Allow pinned SDK to be used for dotnet format command

[lahsrah]

Is your feature request related to a problem? Please describe.

dotnet format command is broken in 9.0.200 that was installed by Visual Studio and no update is available as of now. #46780

I want to be able to run dotnet format command that is part of 8.x.x but it doesn't seem possible. I tried using a global.json file to pin .net 8 to my project but format command still uses 9.0.200 on my machine.

Describe the solution you'd like

dotnet format command to respect pinned sdk in global.json file.

Additional context

global.json to pin dotnet 8 to my project

{
  "sdk": {
    "version": "8.0.406",
    "rollForward": "latestFeature"
  }
}

SDKs installed on my machine:

> dotnet --list-sdks
8.0.406 [C:\Program Files\dotnet\sdk]
9.0.200 [C:\Program Files\dotnet\sdk]

SDK dotnet command uses after pinning via global.json

> dotnet --version
8.0.406 [C:\Program Files\dotnet\sdk]

dotnet build respects pinned version

> dotnet build -v d
Build started 5/03/2025 5:35:58 PM.
     0>Process = "C:\Program Files\dotnet\dotnet.exe"
     MSBuild executable path = "C:\Program Files\dotnet\sdk\8.0.406\MSBuild.dll"
     ...

dotnet format does not respect pinned version

> dotnet format -v d
  The dotnet runtime version is '9.0.2'.
  Formatting code files in workspace 'C:\Data\Code\demo-project\demo-project.csproj'.

[KalleOlaviNiemitalo]

dotnet-format.runtimeconfig.json in .NET SDK 8.0.309 is:

{
  "runtimeOptions": {
    "tfm": "net8.0",
    "rollForward": "LatestMajor",
    "framework": {
      "name": "Microsoft.NETCore.App",
      "version": "8.0.13"
    },
    "configProperties": {
      "System.GC.Server": true,
      "System.Reflection.Metadata.MetadataUpdater.IsSupported": false,
      "System.Runtime.Serialization.EnableUnsafeBinaryFormatterSerialization": false
    }
  }
}

I suppose the "LatestMajor" setting comes from dotnet/format#694. I don't know what that PR was intended to fix and whether "LatestMajor" is still necessary after #38857.

[KalleOlaviNiemitalo]

However, if the .NET Runtime version 9.0.2 causes dotnet-format to fail with the "source text did not have an identifiable encoding" error that is shown in #46780, then that seems a breaking change that may hurt other applications as well.

In contrast, if the error is more connected to the version of dotnet-format itself, then I don't expect that removing the "LatestMajor" setting will fix it.

In my testing with .NET SDK versions 8.0.309, 9.0.103, and 9.0.200 installed and global.json pointing to 8.0.309, the dotnet-format binary came from .NET SDK 8.0.309 even though it was executed on .NET Runtime 9.0.2.