[Question] New Feature support for old projects

[paul1956]

In VB the compiler defaults to features from last major version, currently 15 and if you want to use features of 15.3 or 15.5 you have to specify the version specifically in the project file. When VB 16 come out anyone who didn't specify a specific version automatically gets VB 16 features, including features of 15.3 and 15.5. What happens if they had manually set the language version to 15.3 or 15.5 are those setting deleted, do VB 16 features not work, are they prompted to edit the files or something else?

[KathleenDollard]

If you have feedback on how this should work, let me know and I'll let the folks working on it know.

We hope to have direct changes to VB version in the Visual Studio IDE (yeah!)

We won't change explicit language versions automatically. You would have to do that via the project file or IDE. That would be true if you had explicitly set 15.0 as well - although that would be uncommon.

I hope we can provide an upgrade path similar to C# - if you use a new feature you get a Code Fix to upgrade. That won't be clear until we know more about VB 16 features, because not all features are amenable to that approach.

[paul1956]

The only reason to set version explicitly is to get new features in minor release, I would hope if someone set 15.3 or 15.5 they would be offered option to remove them or at least a warning when 16.0 comes out during first time project opening. I can't imagine how turning on VB 16 would break a program that requested 15.3 or 15.5.
If someone doesn't specify they get VB16
If they specified 15.3 or 15.5 they get VB16 or at least a notification
If they specified something less that 15.3 do nothing
IMHO the CodeFix is needed for the first minor release it could not be necessary in VB16.0

[KathleenDollard]

Thanks for the thoughts.

You point out that VB programmers selecting 15.3 or 15.5 probably intended to be selecting "Latest minor"

[paul1956]

I think C# defaults to "Latest minor" if you don't specify anything in project file, VB default is latest major, Is "Latest minor"even an option in VB, I thought the project file wants a number? At least in my case I wanted latest. This is very confusing.

[zspitz]

@paul1956 From Select the C# language version:

The C# compiler defaults to the latest major version of the language that has been released.

Same behavior as VB.NET.

[paul1956]

@zspitz thanks. The document would be extremely useful for VB, it is the first time I am seeing several of the ways you can set version without editing the project file and details on what you can set.

[zspitz]

@paul1956 You mean like this? Although it seems that currently there is no VB.NET UI option; you have to edit the project files.

[paul1956]

Exactly, thanks. It would be nice if the VS error had a linked to it. I, knew about lack of UI.

[paul1956]

Would a PR be accepted to change the text of the error to include the link?

[KathleenDollard]

@paul1956 The text of which error?

[paul1956]

The error returned for any feature that is not available because the Language Version of the Project is less than the current compiler and the user tries to us it and therefore requires use of the instructions.

ReportFeatureUnavailable handles this error. It currently tells the user what version then need to use but not how to set it. Today ERR_TupleInferredNamesNotAvailable and ERR_ExpectedNamedArgument.