Console/Class lib project templates use latest C# language idioms

[DamianEdwards]

In .NET 6, the included C# project templates will use the latest language idioms.

See the parent Epic for details.

Console template:

• remove app template - removed app template, moved changes to console app instead #3424
• top-level program - removed app template, moved changes to console app instead #3424
• global usings - removed app template, moved changes to console app instead #3424
• nullable - removed app template, moved changes to console app instead #3424

Classlib template:

• global usings - removed app template, moved changes to console app instead #3424
• nullable enable nullable on new project templates #3173 do not enable nullable on netstandard2.0 #3299 remove the --nullable option from the app and classlib template #3396
• file-scoped namespaces- dotnet/templating#3360 using file-scoped namespaces in classlib template #3395

Issues:

• Console and classlib cannot be built when langVersion is set to value less than 10 (net6.0) #3449

@KathleenDollard

[vlada-shubina]

@DamianEdwards

Couple things here:

1. Recently we created new app template (create new console-app template #3248). This template suppose to replace console template. It already has most of the features in and we are adding global usings in Add global using's for console and classlib templates #3344. I can add async Main in same time.

2. Nullables were already added to classlib template: Change C# templates to have #nullable enabled by default #2979. I can add file scoped templates and global usings if needed.

3. Just double checking - any changes needed for other languages (F#, VB)?

[KathleenDollard]

@DamianEdwards There is an enormous amount of tutorials, instructions, books, etc in the wild that has been created over the years. This includes everything from high school curriculum to SO posts and is used by the people that are introducing .NET for us. Given the amount of this information and the fact it fundamentally not working affects our newest customers as they are just trying .NET, we decided that a new template was least disruptive. In addition, the name "console" has meaning only from the perspective of the tech, not naïve intuition. We decided to "freeze" Console, and thus did not add nullable.

For these reasons we added a new "app" template with the expectation that all beginner instructions etc. will change to this template over (hopefully short) time allowing us to make this change without disrupting our new users and have a better name. In addition to the scenario where a teacher hands out instructions that make no sense, someone could rebuild their laptop a week before finals to do some end semester work and be unable to do it. We can instead teach teachers about using these new features and allow them to introduce namespaces and class at the time they think appropriate. Of course we update things that can be disruptive, but this massive change to Console would disrupt the wrong people at the wrong time.

Something else has taken a great deal of time over the last several days, and thus the blog post for templates in Preview 6 was delayed.

[KathleenDollard]

@vlada-shubina There is another change we are working on that will affect global usings overall. So hold off on that change to the app template please.

[DamianEdwards]

@KathleenDollard thanks for the details. Given that context, are we planning on removing console from the default list shown when dotnet new is invoked without arguments? The request here is that all our templates are updated to reflect the latest and greatest language idioms while acknowledging that this could cause friction in some cases. Given the specific concerns RE console and education however, perhaps a compromise of not showing it in the default set is acceptable.

@vlada-shubina no need to add async Main unless the template is already calling Task-returning methods, or calling methods that have Task-returning equivalents.

[vlada-shubina]

@DamianEdwards @KathleenDollard File-scoped namespaces were added in #3395, however these templates cannot be built at the moment, therefore we cannot merge it until it is supported for build.

[DamianEdwards]

@vlada-shubina thanks, this is the compiler issue to watch for them landing the file-scoped namespaces feature in preview.7