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

34
votes

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:

warnings as errors radio button selected

<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.

3
c#c#-8.0nullable-reference-types
Try to add <WarningsAsErrors>CS8600;CS8602;CS8603</WarningsAsErrors> to csproj – Phat Huynh
I think your VS has problem. Same config work for me. Please try to reinstall your VS – Phat Huynh
are you building the project to get these warnings/errors, or is the problem happening in the editor window? there seem to be lots of synchronization issues with the compiler that's running in the code window, but it shouldn't be able to get past an actual build process. – Dave Cousineau
@officer's answer nails what you're looking for. It ought to be accepted as the answer here. – joelmdev

3 Answers

43
votes

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>
7
votes

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.

6
votes

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>

screen

Update:

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

Update 2021-04:

We have this list now: <WarningsAsErrors>CS8600;CS8601;CS8602;CS8603;CS8604;CS8613;CS8614;CS8619;CS8620;CS8622;CS8625;CS8629;CS8633,CS8767</WarningsAsErrors>