C# compiler throws Language Version (LangVersion) reference error "Invalid 'nullable' value: 'Enable' for C# 7.3"

c# nullable c#-8.0 nullable-reference-types

10,946

You should try <LangVersion>preview</LangVersion> as the error message suggests.

10,946

Author by

dnf

Updated on June 04, 2022

Comments

dnf about 2 years
I have solution with couple .NET Standard projects in all I wanted to enable c# 8 and nullable like below:
```
<PropertyGroup>
    <TargetFramework>netstandard2.1</TargetFramework>
    <LangVersion>8.0</LangVersion>
    <Nullable>enable</Nullable>
  </PropertyGroup>
```
The problem is that some projects are compiling fine and some have error:

Invalid 'nullable' value: 'Enable' for C# 7.3. Please use language version 'preview' or greater

I have Visual Studio 16.2 Preview 2 and .NET Core 3 Preview 6. Is this a bug in preview or I'm doing something wrong?
- Panagiotis Kanavos about 5 years
  
  No repro. I use 8.0 too. Do you have a global.json in those failing projects that points to an earlier SDK?
dnf about 5 years

With preview error message is the same
Panagiotis Kanavos about 5 years

preview is 8.0 at this point in time.
Avin Kavish about 5 years

It is not recognized as 8.0 till after release.
crakama over 2 years

If you right click on your project, navigate to "Properties" >> "Build" >> "Advanced" >> "Language Version" you will notice that visual studio does not provide UI to change the value, You may need to Navigate to the csproj file (by right click on each of your project in visual studio and select "Unload Project", to open up the csproj file) of all your projects under your solution and add <LangVersion>preview</LangVersion>. This settings will help your latest C# compiler determine the default language version based on your projects targets framework.