Modify Tizen TFM to support netstandard2.0

[WonyoungChoi]

For Tizen .NET, the TFM version will be restarted from 1.0.
And Tizen 1.x will support .NETStandard 2.0 when .NETCore 2.0 is released.
Thus, the versioning mapping for Tizen 3.x and Tizen4.x are not needed now.

[dnfclas]

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[emgarten]

@WonyoungChoi this change looks good, but there are some conflicts with how this will ship. You have two options.

1. Ship Tizen support in VS 15.1/NuGet 4.1.0 using the existing Tizen3.0/Tizen4.0 but no support for netstandard2.0. Then change this PR to build on that instead of going to Tizen1.0.
2. I can remove Tizen support from VS 15.1/NuGet 4.1.0 and we can ship Tizen for the first time in VS 15.3/NuGet 4.3.0 and go with this PR.

Let me know which release schedule works better for you.

4.1.0 is currently in the release-4.1.0-rtm branch. The dev branch is 4.3.0.

[WonyoungChoi]

@emgarten Can I know when VS 15.3/NuGet 4.3.0 is released?

[emgarten]

@rrelyea for the timelines

[WonyoungChoi]

@emgarten We'd better choose the first option. Using Tizen TFM on time is more important than supporting netstandard 2.0.
Please just ship Tizen support in VS 15.1/NuGet 4.1.0 without supporting netstandard2.0.
I am going to change this PR so that Tizen3 supports netstandard2.0 in VS 15.3/NuGet 4.3.0.

Using Tizen 1.0 is cancelled.

[emgarten]

@WonyoungChoi should it be that Tizen5.0 supports netstandard2.0 instead?

What you have in this PR is:
Previous mappings:
Tizen3.0 -> netstandard1.6
Tizen4.0 -> netstandard1.7

New mapping:
Tizen3.0 -> netstandard2.0

If Tizen4.0 will already be shipping with 4.1.0 then you need to keep that mapping.

I would instead expect it to be:
Tizen3.0 -> netstandard1.6
Tizen4.0 -> netstandard1.7
Tizen5.0 -> netstandard2.0

[emgarten]

@WonyoungChoi could you also let me know what the plan is for future releases of Tizen, will each one be a new version and old ones will stay the same? Or will older versions such as Tizen3.0 be updated to include new APIs?

[WonyoungChoi]

We are going to update Tizen 3.0 to support .NETCore 2.0 this year.
And also Tizen 4.0 are going to be released at the end of year.

I think the new mapping has no problem.
In NuGet 4.1.0, Users can use either tizen30 or tizen40, and restore netstandard1.6 or 1.7.
In NuGet 4.3.0, Users can also use either tizen30 or tizen40, and restore netstandard2.0.
Even there is no package using Tizen TFM yet.

Although we and users are not able to use netstandard2.0 until NuGet 4.3.0 is released,
it is not a big problem because it is possible to develop Tizen .NET API with ns 1.6 now.

I know this is not a clean solution.

If there is strict rule that must keep existing mapping, it is possible to keep Tizen3 and change Tizen4 to support ns2.0 only.
Tizen3 -> netstandard1.6
Tizen4 -> netstandard2.0

[WonyoungChoi]

I am sorry for the confusion.

I'd like to just change Tizen4 to support nestandard 2.0 instead of 1.7.
("1.7" was a placeholder indicating the newer version of netstandard in dev branch)

[emgarten]

@WonyoungChoi are you still planning to update Tizen3.0 to support netstandard2.0 in the future? Will any releases be updated in the future without incrementing the version number?

[WonyoungChoi]

@emgarten
There was a lot of discussion internally yesterday.

The Tizen TFM version will refer to API level of Tizen .NET.
And it will be used separately from the native Tizen Platform version.

It is possible that Tizen 3.0 will be updated again after Tizen 4.0 is released.
But, Tizen TFM will use incrementing version number always.

for example, (THIS IS JUST AN EXAMPLE)

Tizen5 TFM can be used in Tizen 3.x platform.

(Platform - TFM -> Supports)
Tizen3.0 - tizen3 -> netstandard1.6
Tizen4.0 - tizen4 -> netstandard2.0
Tizen3.1 - tizen5 -> netstandard2.1
Tizen4.1 - tizen6 -> netstandard2.5

[WonyoungChoi]

In addition,
Tizen .NET is an independent solution that can be installed on the Tizen Platform.

[emgarten]

Tizen TFM will use incrementing version number always.

This sounds like a good idea, it will make it much easier for package authors if the version matches the API surface area.

Should Tizen4.0 be removed from the NuGet 4.1 release and only added here to NuGet 4.3?

[WonyoungChoi]

@emgarten
In Nuget 4.3, it is not necessary to remove Tizen4 TFM from the NuGet 4.1 if it is possible to just modify it according to this PR because Tizen4 TFM is not used anywhere yet and it is latest version of Tizen TFM currently.

[mishra14]

Looks good to me!

[emgarten]

Thanks for the explanation @WonyoungChoi, I've merged this into dev branch, it will go in 4.3.0 with the rest of the netstandard 2.0.0 support.