Docs: Asp.Net still compiles with C# 7.0, even when .Net 4.8 is installed

[PoulBak]

Although .Net 4.8 is installed and it should default to C# 7.3, asp.net still uses C# 7.0 - even in Visual Studio 2019.

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Document Details

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• ID: 5694e62b-c756-1f62-4014-2ceafa54c011
• Version Independent ID: 3f01c378-22e4-197c-a862-ab4a924506c7
• Content: C# language versioning - C# Guide
• Content Source: docs/csharp/language-reference/configure-language-version.md
• Product: dotnet-csharp
• GitHub Login: @BillWagner
• Microsoft Alias: wiwagn

[cartermp]

@PoulBak Thanks! You are correct, C# 7.3 should by the default. This sounds like a product bug if it reproduces with new ASP.NET projects - I'm assuming old-style ASP.NET here, since you mention .NET Framework - and the appropriate avenue here would be the Visual Studio Report A Problem tool.

I'd also double-check that you don't have a props file (e.g., Directory.build.props) setting the LangVersion for you in a way that defaults to C# 7.0.

[DaveSneddon]

I have the version "Automatically selected based on framework version" for me which Automatically selects 7.0 and doesn't allow me to change it. How do I turn this useless "helpful" feature off? Using VS 2019 16.3.7 with .NET 4.7.2.

[PoulBak]

@cartermp I don't have a props file. This is not new, it has been like that for several years. Asp.Net uses the 'Latest Major' compiler.
@DaveSneddon The only way to get the C# 7.3 compiler in asp.net is to install 'Microsoft.CodeDom.Providers.DotNetCompilerPlatform' from Github (and distribute it to your server). You must set the langversion to 7.3 in web.config.

[BillWagner]

@DaveSneddon @PoulBak Is your project an ASP.NET Core project, or an ASP.NET project?

/cc @danroth27 who may have more insight.

[PoulBak]

It's an asp.net classic WEBSITE (which gets compiled by the server).

[cartermp]

I'll defer to ASP.NET folks (such as @danroth27) on whether or not the legacy website project kinds should support later C# versions, but my intuition is no, given the abundance of features that depend on types (and now runtime features with Default Interface Members) that are only available on .NET Core.

[PoulBak]

Why should asp.net websites be different than other .Net Framework? That's the question here. C# 7.3 is DEFAULT for all other .Net Framework projects.

[DaveSneddon]

@BillWagner mine is a ASP.NET project. @PoulBak thanks for your help, I've got it working now. I already had the latest DotNetCompilerPlatform package but the langversion was set to 'default'. Changing it to 'latest' fixed the issue. Why 'default' isn't 7.3 doesn't make sense to me.

[Thraka]

I'm going to close this since your question seems to be answered on how to enable 7.3. Regarding defaults though, I'm unsure who you should raise this to. https://github.com/aspnet/AspNetWebStack/ perhaps?