Allow installing .NET patch versions side by side

[cmeeren]

I currently have 7.0.102 installed. For debugging purposes, I would like to install 7.0.101 and force that exact version using global.json. However, the installer refuses to install 7.0.101 because "another version of the product is already installed". To be able to install, I have to modify my VS installation to remove the .NET SDK altogether (which also removes other stuff I would like to not touch), remove versions installed through Chocolatey, etc.

For examples of problems where this kind of installation/pinning/debugging make sense, see e.g. dotnet/fsharp#13678 and dotnet/fsharp#14618.

[KalleOlaviNiemitalo]

Perhaps dotnet-install scripts can install a version to a separate directory no matter which other versions have been installed.

[baronfel]

That's right - it's an explicit design goal of the microsoft-authored installers and packages that patch versions be automatically updated. This is partially to help with the automatic update story with systems like Microsoft Update/debian unattended updates - for security reasons path updates should remove the (presumed vulnerable) previous versions.

I would recommend the dotnet-install scripts as an interim solution.

[collinstevens]

This is a pain point with the current preview versions of .NET SDKs.

The latest versions of the .NET SDK after 8.0.100-preview.3.23178.7 require you to use the preview version of Visual Studio (17.7 at time of writing) due to the Rosyln package version being updated to 4.7.0.0. https://learn.microsoft.com/en-us/visualstudio/extensibility/roslyn-version-support?view=vs-2022

I can specify 8.0.100-preview.3.23178.7 in the global.json and downgrade myself and repositories I maintain within my organization, but this now means I am unable to work on other projects which are using the latest .NET SDK preview versions because we can not have a side-by-side installation of these patch versions.