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

Question

Using Visual Studio 2019 v16.3.2 with a .NET Core 3.0 project set to C# 8 and nullable reference types enabled.

<PropertyGroup>     <TargetFramework>netcoreapp3.0</TargetFramework>     <LangVersion>8.0</LangVersion>     <Nullable>enable</Nullable> </PropertyGroup>  

If I set it to treat all warnings as errors:

<TreatWarningsAsErrors>true</TreatWarningsAsErrors> <WarningsAsErrors /> 

It reports other warnings as errors. For example, CS0168 The variable 'x' is declared but never used is reported as an error. But all the nullable reference warnings are still reported as warnings. For example, CS8600 Converting null literal or possible null value to non-nullable type. is still reported as a warning.

How do I treat all nullable reference warnings as errors?

Note: even setting CS8600 specifically to be treated as an error doesn't cause it to be reported as an error. If that worked, it still wouldn't help with treating them all as errors because there are so many.

Edit: setting specific warnings to be treated as errors puts <WarningsAsErrors>CS8600;CS8602;CS8603</WarningsAsErrors> in the csproj and doesn't work.

Answer 1

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>  

Answer 2

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.