Support .NET 7 for Fable 3?

[MangelMaxime]

Description

I see more and more people reporting issues with their dependencies not being found.

The cause of the error is that Fable 3 doesn't support .NET 7 but because the error is not obvious they can't figure it out.

Would it be possible to post the changes made for Fable 4 to Fable 3? If not is it possible to detect the error and indicate to the user to add a global.json to their project to lock to .NET 6?

Option 1 would be better if doable :)

[MangelMaxime]

Workaround:

Create a global.json with the following content:

{
    "sdk": {
        "version": "6.0.0",
        "rollForward": "latestMinor"
    }
}

This will tell dotnet to use .NET 6 for the current directory and children.

The other solution is to move to Fable 4 (in beta stage at the time of writing).

[AlbertoLeon]

Maybe another approach is update the template with this approach and also, adding the Fable 4 templates?

[AlbertoLeon]

There is a complete log after adding the global.json

[MangelMaxime]

@AlbertoLeon The template has been updated to include a global.json file.

https://github.com/fable-compiler/fable-templates/blob/master/minimal/CHANGELOG.md#390---2021-12-12

Make sure you deleted all temporary artefacts like bin and obj folders. One way to do it in general is to commit your work and then run git clean -xdf to remove all the files that are not tracked

[MangelMaxime]

@alfonsogarciacaro

I think not having support of .NET 7 or an error report in Fable 3 is hurting Fable. This is because new users and even old users are hitting a wall and they don't know what is happening.

This can lead to frustration and less adoption of Fable.

Are the changes required to support .NET 7 in Fable 3 complex? Would checking dotnet --version be enough to provide an hint for a solution to the user?

[object]

I second @MangelMaxime's proposal. This failure can be quite frustrating because the error message doesn't give a clue about possible cause of failure except that it looks like nothing works. With growing .NET 7 adoption it's quite important to enhance Fable 3 with support for it.

[ken-okabe]

Readme suggests

• dotnet SDK 6 or higher

and looking at the page

.NET 7.0
Standard Term Support
Recommended

and
.NET 6.0 became LTS

#3028 (comment)

Fable 4 is already looking very nice.
Is there a timeframe for a ready-for-production Fable 4 release?

I also wish Fable4 become the production-ready release with the official templates soon.

[rfrerebe]

I think this issue should be pinned above all issues until it's solved.
I think it would help.

[kspeakman]

VS 2022 requires .NET 7 for most of its workloads. So now all my existing Fable projects are broken. Why is a global.json file required to fix this? The project already has net6.0 as the SDK version in the project file. AFAIK, this is what VS uses to compile to net6.0 even tho dotnet --version reports 7.

[MangelMaxime]

The global.json is required to force .NET to use the correct version.

This is because something changed in .NET 7 in how dependencies resolution should be done (like with every release of .NET I think...)

If you use the global.json file with the setting I provided then dotnet --version should return 6 otherwise you probably miss configured that file.

[kspeakman]

Point is: dotnet build compiles to net6.0 even with 7 installed, presumably because it uses the target SDK version from the .fsproj file. Could Fable use a similar strategy?

Simply having .NET 7 installed -- which is now a prerequisite for most VS 2022 workloads -- breaks all Fable 3 projects. It is very disconcerting when a project suddenly and inexplicably stops working. Adding a global.json is a work-around, but only after half a day of trying to figure it out, confidence destroyed.

[MangelMaxime]

Point is: dotnet build compiles to net6.0 even with 7 installed, presumably because it uses the target SDK version from the .fsproj file. Could Fable use a similar strategy?

It could if dependencies resolution is fixed when running with .NET 7.

You can install several version of dotnet side by side, so you can have both .NET 6 and .NET 7 installed at the same time.

Simply having .NET 7 installed -- which is now a prerequisite for most VS 2022 workloads -- breaks all Fable 3 projects. It is very disconcerting when a project suddenly and inexplicably stops working. Adding a global.json is a work-around, but only after half a day of trying to figure it out, confidence destroyed.

Indeed, this bug is annoying.

In general, it is a good idea to lock your runtimes in the same way you do it for your dependancies. This help makes the code reproducible between machines and easier to spot why something is breaking.

[kspeakman]

I do have both SDK versions installed. (Even if I didn't, later SDK versions will typically compile to older targets.) But the correct target is specified in the .fsproj file. The dotnet build tool has the -r <runtime identifier> option. But I don't have to use that to get it to compile net6.0 -- it does so by itself. So it seems possible for Fable to avoid this issue going forward, too.

update: Just adding global.json file without having NET 6 SDK installed, project won't build. Have to manually install .NET 6 SDK too. Or downgrade to VS 17.3 (17.2 is LTS) to avoid all of this. NET 7 was added in 17.4.

[PaigeM89]

For what it's worth, this story gets a bit more complex on linux - or at least it was weird for me on Ubuntu.

I had the 6.0.406 and 7.0.200 dotnet SDKs installed, but even with the global.json configured to point at 6.0.406 I was having issues where Fable would hang with no output when I tried to run it.

I'm adding this anecdote for 2 reasons:

1. It's a use case for getting Fable 3 to support dotnet 7, to avoid the headache I ran into.
2. It may be of help to someone running into the same issues.

For anyone stumbling across this issue and having similar symptoms, I had to manually extract the dotnet 6 binaries & copy the content of shared/Microsoft.NETCore.App/6.0.14 over to /usr/share/dotnet/shared/Microsoft.NETCore.App/ before Fable would give me output. My global.json was unchanged, still pointed at 6.0.406.

[JoostVanVelthoven]

How is this issue prioritized?

[MangelMaxime]

We don't have a blog post announcement yet, but today Fable 4 has been released with JavaScript considered stable.

The idea is that the maintainers want to avoid spending time fixing issues in Fable 3, and encourage people to move to Fable 4 in order to get the latest features ans support for .NET 7 is part of it.

[kspeakman]

This break occurs from a supposedly backward compatible tool update and the cause is hard to discover. (Google didn't find it... a kind soul on F# slack directed me here.) Is there no way to address this economically?

Asking everyone to upgrade to a newly released major version is pretty intense.

[MangelMaxime]

I would love to have it supported in Fable 3 or at least have an explicit error message.

However, the main maintainers of Fable are focused on Fable 4 now. I tried to port the changes from Fable 4 to Fable 3 but encounter errors that I don't understand. My PR his here: #3363

I think if someone is able to make my PR work or submit another PR that works or improve the situation we could have it accepted. Contributions are always welcomed