Add support for authoring Azure Functions as .NET Core class library

[pscholtes]

Add support to the "Azure Functions and Web Jobs Tools" extension within Visual Studio for authoring Azure Functions as a .NET Core class library. This issue is a spin off from a conversation started in #686 and is possibly, semi-related to #790.

When creating a new Azure Function app, you must select between the versions "v1 (.NET Framework)" or "v2 (.NET Standard)".

1. If v1 is selected, you can target any version of the .NET Framework <= 4.6.1
2. If v2 is selected, you can target any version of .NET Standard <= 2.0

Neither option allows the resulting Azure Function project to target .NET Core 2.x.

Scenario
Given the following VS solution/project architecture for Company Xyz:

• Xyz.Common .NET Core 2.x shared library leveraging EF Core and various 3rd party packages
• Xyz.Web ASP.NET Core Web Application leveraging AspNetCore.All, EF Core, Controllers, etc.
• Xyz.Functions v2 Azure Functions project with HTTP, timer, and queue triggers

Problem
When a project reference is added from Xyz.Functions to Xyz.Common Visual Studio generates a "project not compatible" build error as these two projects reference different frameworks (i.e. .NET Standard != .NET Core).

Reasoning
In a "real word" enterprise-level application, it's a very realistic expectation for a developer to centralize the logic for a specific processing routine and want to leverage that code from an IActionResult in a MVC app and a [TestMethod] in a MSTest project. Continuing with that approach, AF should allow a developer to leverage their .NET Core code from a Trigger as well.

[paulbatum]

Some of the discussion in this issue is relevant - it provides steps that can get a function app with target netcoreapp2.0 compiling, but not running:
Azure/azure-functions-vs-build-sdk#160 (comment)

This is the error you'll get if you try this:

It would be good to understand whether we expect to be able to get this working. I don't understand the details so I'm tagging Fabio Cavalcante (@fabiocav).

[hanblee]

FYI, as mentioned in #836, AWS Lambda allows one to target netcoreapp2.0 (https://aws.amazon.com/blogs/developer/aws-lambda-net-core-2-0-support-released/).

[pscholtes]

Hey Paul Batum (@paulbatum), in #836 (comment) you mention that more "investigation" is required for this issue. I am just curious, but is this issue in active discovery/development on the MSFT side? Do you have any updates or roadmap for support? Thanks!

[paulbatum]

We're not spending cycles on this at the moment but we intend to in the coming months.

This issue is pretty much holding me from using Azure functions. Please spend cycles on this. Its keeping developers with existing .NET Core libraries on the WebJob side.

[MisinformedDNA]

Since this won't happen for a few months, at least, could your libraries target .NET Standard instead? If not, what is blocking that?

Its too much impact compared to the worth of the improvement. Im not suddenly targeting my production libraries to .NET standard. Its a fundamental change which requires full application testing and staging. Not something I put on my sprint that easy.

[pscholtes]

I'm seeing that with version 15.0.40617.0 of the AF extensions, you can pick either the v1 (.NET Framework) or the v2 (.NET Core) project template. When v2 is selected the resulting project still targets the .NET Standard framework.

In tracking this issue I recall that this is more or less how the extensions worked when v2 was introduced (i.e. choose v2 (.NET Core), but the project targets Standard); however, this confusion of Core/Standard was first discussed in #686 with Naren Soni (@soninaren) where ultimately it was changed to read v2 (.NET Standard) in 15.0.40502.0.

The 15.0.40617.0 release notes state that:

The tools will run v2 Azure Functions locally against .NET Core 2.1.

Paul Batum (@paulbatum) not trying to understate the nuances/complexities of this, but can you please provide any updates or insights related to the aforementioned changes?

[paulbatum]

Hi Phillip Scholtes (@pscholtes), unfortunately I dont have much else to add right now. The VS tooling has been built and tested to use class libraries that target .NET Standard, and there are technical problems that need to be worked through to allow you to work with class libraries that target .NET Core. We want to investigate but its not sitting at the top of our list of must-fix issues so I have no progress to report at the moment.

[thierry-prost]

The situation described by pscholtes's "real-life application" is exactly what our company is facing. It would mean the world if the issue could be prioritized. We've been looking at the github issues for months now with no real update on this.

[sfmskywalker]

I need Functions to target .NET Core as well.

In my case, I have a .NET Core class library that utilizes HttpClientFactory which today only exists in .NET Core. If I want to use Functions v2 and leverage this class library, it needs to target .NET Standard 2.0, which means managing HttpClient myself. Knowing all there is to know about HttpClientFactory, I really rather not :)

I wanted to look for a UserVoice idea on this, and turns out one does exist and is actually marked as "Completed"! But alas, although the title says "Support for NET Core", it was completed with support for NET Standard :(

[MisinformedDNA]

HttpClientFactory supports .NET Standard. See project file and NuGet. Hope this can unblock you for now.

[Tealons]

This also a blocker for us. Would be nice to get this fixed in the near future!