2.0 C# language versions ASP.NET Core projects (project, Razor, scaffolding)

[Rick-Anderson]

As dan roth for more details

[guardrex]

@Rick-Anderson Can you say more about what this one entails?

[Rick-Anderson]

See #5591

[guardrex]

Title: Language support in ASP.NET Core projects

Notes:

• Configuring the ASP.NET Core project's language versions in VS isn't intuitive. VS uses the "hidden UI" (referring to project Properties > Build panel > Advanced > Language version DDL).
• Talks about Razor, scaffolding, C#, publishing ... because they all get impacted by the version of Roslyn compiler that you bring in as a dependency versus what gets compiled by VS.
• Update to use the latest Roslyn version and add support for C# 7 aspnet/Razor#1046
• Important! 👉 UpgradeProject should recognize ASP.NET and ASP.NET Core projects roslyn#20614
• [Umbrella] Improving compiler adoption and dogfooding story roslyn#18783
• @davidfowl says not to document use of a preview compiler. It requires some sort of very custom VS setup.

It looks like this basically boils down to one main thing (as stated by @jcouv) ...

[When the IDE seems fine with new C# syntax, but the app 💥 at runtime, this] is caused by a mismatch between the built-in compiler (used by VS) and the compiler pulled in as a nuget package by ASP.NET projects.

[guardrex]

@Rick-Anderson @mairaw @BillWagner

It looks like this ask on this issue has been addressed to some degree. See 👉 https://docs.microsoft.com/dotnet/csharp/whats-new/csharp-7-1#language-version-selection

However, it was written for 7.1. The 7.2 topic didn't receive a similar section.

Perhaps to better surface the content, should that section become its own topic and be written to generically apply to C# versions? ... perhaps under https://docs.microsoft.com/dotnet/csharp/whats-new/

[BillWagner]

We have an issue for this: dotnet/docs#3685 Do you want to take it on?

If you search the docs repo for <LangVersion> you'll find the locations that should link to the new topic.

dotnet/docs#4154 is also relevant. I don't think the .NET Core SDK / CLI has an answer for that yet though. @danroth27 do you have ideas here?

[guardrex]

Do you want to take it on?

It doesn't matter to me, but I've been ordered not to work on other repos while on contract. I need approval.

@Rick-Anderson Do you want to close this as a dup of dotnet/docs#3685? Do you want to approve my working dotnet/docs#3685?

[Rick-Anderson]

@guardrex I think @JRAlexander can handle it.

[JRAlexander]

@Rick-Anderson Handle what?

[guardrex]

@JRAlexander He's referring to dotnet/docs#3685. This issue is a dup of that one.

[JRAlexander]

Ok, I'll talk with @BillWagner and @mairaw to see if this should be included in the .NET 2.1 project. Thanks!