[dotnet][dotnet-vnc] Fix image builds

[jankeromnes]

As suggested in https://webcache.googleusercontent.com/search?q=cache:CfIV54IT1KAJ:https://docs.microsoft.com/en-us/dotnet/core/install/linux-package-manager-ubuntu-2004+&cd=1&hl=en&ct=clnk&gl=fr&client=firefox-b-d

[jankeromnes]

Still fails with:

Reading package lists...
Reading package lists...
Building dependency tree...
Reading state information...
E: Unable to locate package dotnet-sdk-3.1
E: Couldn't find any package by glob 'dotnet-sdk-3.1'
E: Couldn't find any package by regex 'dotnet-sdk-3.1'

I guess the fall back is to drop the .deb file and install binaries instead, as described in: https://dev.to/carlos487/installing-dotnet-core-in-ubuntu-20-04-6jh

[jankeromnes]

New approach. Still left to do:

• Re-install fsharp and mono-complete
• Install mono-devel to fix fsharpi (i.e. absorb Fix fsharpi #195)

[jankeromnes]

Woohoo, it worked! 🎉

[jankeromnes]

Ok, so the new Ubuntu 20.04 gitpod/workspace-dotnet* images now build successfully again.

However, I don't know .NET well enough to know whether it's okay to just install:

• .NET Core SDK 3.1
• mono-complete
• fsharp

We used to (potentially) install a few extra things, e.g.:

• The previous image used ACCEPT_EULA=Y apt-get -y -f -o APT::Install-Suggests="true" install instead of just apt-get install -y. Will we miss anything important if we don't install suggested packages?

• In Fix fsharpi #195, mono-devel was also installed (in addition to mono-complete). Is that needed, e.g. to fix fsharpi?

@JesterOrNot @simonelnahas @jhuizingh Would you have any insights on the questions above?

Otherwise, I guess the next step would be to test the new images, and see if they work with "real" .NET projects:

• gitpod/workspace-dotnet:branch-jx-fix-dotnet
• gitpod/workspace-dotnet-vnc:branch-jx-fix-dotnet

[jankeromnes]

Well, I guess "maybe fixed" is better than "definitely broken", so I'll merge this PR, and we can make any adjustments as follow-up PRs.

Thanks again for your patience and help! Let's make .NET development in Gitpod awesome. 🚀

[jhuizingh]

Sorry, meant to respond sooner. I think just the sdk is good for what I'm trying to do.

[jankeromnes]

No worries (and in fact, sorry for being hasty, even though it's a prolonged weekend...) Many thanks for your reply! 🙏