Remainder: Set RollForward once we upgraded to .NET core 3.0

[rusanov-vladimir]

I'm trying to run fake 5 script on ubuntu using latest .NET core 3 preview5.

I uninstalled previous SDK versions so it's the only .NET core version I got.
After installing global tool with dotnet tool install fake-cli -g
I'm getting error above:

It was not possible to find any compatible framework version
The specified framework 'Microsoft.NETCore.App', version '2.1.0' was not found.

• The following frameworks were found:
  3.0.0-preview5-27626-15 at [/home/st/dotnet/shared/Microsoft.NETCore.App]

You can resolve the problem by installing the specified framework and/or SDK.

The .NET Core frameworks can be found at:

• https://aka.ms/dotnet-download

Seems to be similar to #1974.

Is there any reason why fake cannot run on dotnet core 3.0 preview?

[baronfel]

Until fake is published for 3.x, it's not going to run on it successfully. Global tools are runtime-dependent, not self-contained, and so running them requires a compatible runtime to be present on the system. The runtime resolution rules can be found here, but the long and short of it is

• first check within the same major/minor for a compatible patch version
• if none found, look for a compatible minor version
• else fail

It looks like you're hitting the third case, because FAKE is compiled for 2.1, which means it works on 2.1 and 2.2 runtimes.

[matthid]

Well they introduced some roll-forward settings we "could" use:

https://docs.microsoft.com/en-us/dotnet/core/whats-new/dotnet-core-3-0#major-version-roll-forward

-> We could add RollForward=Major to the project file

https://docs.microsoft.com/en-us/dotnet/core/whats-new/dotnet-core-2-1#roll-forward

-> You can use DOTNET_ROLL_FORWARD_ON_NO_CANDIDATE_FX=2 and DOTNET_ROLL_FORWARD=Major as environment variable

[rusanov-vladimir]

Thanks for the answers!
I was aware about runtime resolution rules, but it seemed too awkward that net core 3.0 is backward compatible with 2.x but I wasn't able to run fake with it. Using environment variables I'm able to run fake smoothly without installing older runtime. I think adding RollForward=Major to the project would be great to have this behavior out of box without the need of using environment variables.
Thanks again!

[matthid]

@rusanov-vladimir Thanks for confirming that this actually works ;)

[matthid]

Ok, I'm labeling this as "extern" because dotnet SDK 3 is not yet released. I'm no longer playing around with previews. However, I would probably accept a PR updating all the required places. Considering there is a workaround I'll leave this open as a reminder until SDK v3 has shipped. Please feel free to remind me about this issue when that happened :)

[matthid]

This should be solved in 5.16 due to #2372