Update for compatibility with .NET 5

While I can use the latest Microsoft.NET.Sdk.Functions package to build against .NET 5, the tools will not let you run it locally. Running a complied set of functions causes this this output in the tools:

System.Private.CoreLib: Could not load type 'System.Diagnostics.DebuggerStepThroughAttribute' from assembly 'System.Runtime, Version=4.2.2.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'.
Value cannot be null. (Parameter 'provider')

[anthonychu]

I can share a bit on the decision making and prioritization process and how we got here. Back in the spring of 2020, we surveyed some folks that included Microsoft MVPs and discussed our options for .NET 5. The main takeaways were that we should build an out of process worker for .NET 5. And 2/3 of folks expressed that they plan to stay on .NET Core 3.1 instead of upgrading to .NET 5, so we did not feel there was overwhelming demand. Looking back, in hindsight, there was not a lot of solid details on .NET 5 and it made sense that folks were less excited about it at that time.

We also looked at runtimes like Node, where it is generally expected that platforms do not support non-LTS versions.

So over the summer, we started working on building an out-of-proc worker from scratch. It has taken us longer than expected to ship it. We had planned for the preview to land when .NET 5 GA’d, and that it would GA by end of 2020. We’ve slipped by a couple of months.

As for the assertion that 1 year is a long time, perhaps that’s true. But we’re also looking at what happens after that 1 year. There’s a small 3-month window to ship a new version of the host with the .NET 6 GA bits, and migrate all customers off the .NET 5 host. We didn’t feel that we should take a chance that we’d still need to run on .NET 5 after its end of life.

We want to provide timely support for LTS versions of .NET. We learned from .NET Core 3.1 that we need to more closely match the .NET release dates. We plan on updating the host to .NET 6 and having it available close to .NET 6 GA.

What we underestimated was the demand for non-LTS versions. We want to do better here. It’s too early to tell what this will look like but I think will largely depend on the feedback on the .NET 5 worker.

[jeffputz]

@anthonychu yikes, that’s a pretty serious adoption blocker for .NET 5. I don’t have many projects that don’t involve functions.