How to treat ALL C# 8 nullable reference warnings as errors?

It is now possible to treat all nullable-related warnings as errors without explicitly specifying them all. To achieve this, you have to set <WarningsAsErrors>nullable</WarningsAsErrors> in your *.csproj file [source].

Full example:

<Project Sdk="Microsoft.NET.Sdk.Web">
  <PropertyGroup>
    <TargetFramework>netcoreapp3.1</TargetFramework>
    <Nullable>enable</Nullable>
    <WarningsAsErrors>nullable</WarningsAsErrors>
  </PropertyGroup>
</Project>

The problem was that the .editorconfig file was overriding the Visual Studio setting to treat all warnings as errors with many lines like:

dotnet_diagnostic.CS8602.severity = warning

This forces CS8602 to be a warning.

How this happened: In a previous attempt at turning all nullable reference warnings into errors, I set many of them as errors in the editor config. In that, I discovered both that there were a ton of different warning numbers and that my codebase wasn't ready for them to be errors throughout the entire solution. So I set them to "warning" in the editor config because I didn't want to lose the list of warnings I had found. Then later, having forgotten all about that, I decided to turn on treat warnings as errors on a project by project basis.

I would suggest to use this solution. It mentions all 3 errors and IMHO better solution

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp3.1</TargetFramework>
    <LangVersion>8.0</LangVersion>
    <WarningsAsErrors>CS8600;CS8602;CS8603</WarningsAsErrors>
  </PropertyGroup>
</Project>

---

Update:

We have this list now: <WarningsAsErrors>CS8600;CS8601;CS8602;CS8603;CS8613;CS8625;CS8629;CS8614;CS8619;CS8633</WarningsAsErrors>