How to fix Visual Studio 2022 Warning CA1416 "Call site reachable by all platforms" but "only supported on: 'windows'"?

Question

So I have a C# class library project that I only intend to use on Windows. It contains some classes that use the System.Drawing.Image class which is only available on Windows. After upgrading to Visual Studio 2022 and setting the target framework to .NET 6.0 I'm seeing a bunch of warnings that say:

CA1416 "This call site is reachable on all platforms. 'SomeClass.SomeMethod' is only supported on: 'windows'.

See screenshot below for some examples:

In some sense, it's cool that VS2022 has scanned the library and found all the platform specific code that I'm using in the library. But I'd like to tell VS that I only plan to use the library on windows and it can mute all those warnings.

First I checked the Target framework option in the properties of the project but didn't seen any windows specific targets.

Then I decided to edit the project's .csproj directly and changed the Target framework from

<TargetFramework>net6.0</TargetFramework>

to

<TargetFramework>net6.0-windows</TargetFramework>

But, sadly, even after a recompile, that didn't make the warnings go away either. So then I did some reading on the CA1416 warnings and sure enough it says in the Microsoft Docs that the target framework moniker is ignored for assessing this warning, however, VS does add an attribute to the project based on the TFM that influences this warning, but it only does so if the project is configured to generate the AssemblyInfo.cs file on the fly. But, alas, my project's AssemblyInfo.cs is maintained as a actual file rather then having it auto generated at build time.

So at this point, I'm ready to punt the ball and just disable CA1416 warnings for my project. So in the project's .proj file I added CA1416 for both the release and debug builds like so:

<PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">
    <NoWarn>1701;1702;CA1416;</NoWarn>
</PropertyGroup>

<PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|AnyCPU'">
    <NoWarn>1701;1702;CA1416;</NoWarn>
</PropertyGroup>

One would think that would be the end of those pesky warnings. (sigh) As it turns out, after rebuilding the project the warnings still show up. Got any suggestions? I'm all ears.

Answer 1

I had success removing the CA1416 warnings by adding the following decorator to the top of the containing class:

[System.Runtime.Versioning.SupportedOSPlatform("windows")]

I'm only on VS2019 and using .net 5, but it may work for you. I tried this with VS2019 .net5 console project (top of class Program) and a .net5 class library (top of the class). I added the System.Common.Drawing nuget package. My code included:

string inputPath = @"C:\mypath\mypng.png";
Image i = Image.FromFile(inputPath);

Answer 2

Update:

Targeting Windows worked fine until one of our developers tried to start the solution on his Apple computer using Visual Studio 2022 for Mac Preview 1.

https://learn.microsoft.com/en-us/dotnet/fundamentals/code-analysis/quality-rules/ca1416

Reading .NET 6 Breaking changes Microsoft has a section about System.Drawing.Common.

https://learn.microsoft.com/en-us/dotnet/core/compatibility/core-libraries/6.0/system-drawing-common-windows-only

Their recommendations are the following:

To use these APIs for cross-platform apps, migrate to one of the following libraries:

• ImageSharp
• [SkiaSharp][2]
• [Microsoft.Maui.Graphics][3]

Alternatively, you can enable support for non-Windows platforms by setting the System.Drawing.EnableUnixSupport runtime configuration switch to true in the runtimeconfig.json file:

{
   "runtimeOptions": {
      "configProperties": {
         "System.Drawing.EnableUnixSupport": true
      }
   }
}

This configuration switch was added to give cross-platform apps that depend heavily on this package time to migrate to more modern libraries. However, non-Windows bugs will not be fixed. In addition, we may completely remove support for non-Windows platforms in a future release, even if you enable it using the runtime configuration switch.

Note

Despite the name of the runtime switch, System.Drawing.EnableUnixSupport, it applies to various non-Windows platforms, such as macOS and Android, which can generally be considered flavors of Unix.

Even though Microsoft.Maui.Graphics is in preview and is considered an experimental library I tried to use it given that Microsoft has the library as a recommended action library.

It seemed really promising at first but then I encountered a bug in their IImage Downsize method.

https://github.com/dotnet/Microsoft.Maui.Graphics/issues/247

Until that is fixed my temporary solution is using Target framework .NET 6, Target OS (none) and then use Exclude specific warnings as errors given that we have enabled Treat warnings as errors.

I have also created a runtimeconfig.template.json in our web project root with the following values:

{
   "runtimeOptions": {
      "configProperties": {
         "System.Drawing.EnableUnixSupport": true
      }
   }
}

Original:

You can suppress the warning with dotnet_diagnostic.CA1416.severity = none but imao if you only intend to use it on Windows you should set Target OS to Windows for the project which will fix the warning.

https://learn.microsoft.com/en-us/dotnet/core/compatibility/code-analysis/5.0/ca1416-platform-compatibility-analyzer

Source:

https://stackoverflow.com/a/70272543/3850405