LibraryImport causes CS8795

[FlsPrpht]

Version Used:
VS 17.10.5
.NET Runtime is 8.0.7
.NET SDK - 8.0.303.

Steps to Reproduce:
I cannot reproduce this with a newly created project and have been unable to deduce the difference between my app and the same app.

namespace CS8795
{
    using System;
    using System.Runtime.InteropServices;

    internal static partial class NativeMethods
    {
        [LibraryImport("user32.dll")]
        [return: MarshalAs(UnmanagedType.Bool)]
        internal static partial Boolean IsIconic(IntPtr hwnd);
    }
}

Diagnostic Id:

error CS8795: Partial method 'NativeMethods.IsIconic(nint)' must have an implementation part because it has accessibility modifiers.

Expected Behavior:
Per dotnet/vscode-csharp#5999 we should not be seeing this anymore

Actual Behavior:
I am seeing

error CS8795: Partial method 'NativeMethods.IsIconic(nint)' must have an implementation part because it has accessibility modifiers.

[huoyaoyuan]

This is because the library import generator doesn't run successfully. It doesn't "cause" the error, the absence of it causes.

The linked issue from vscode-csharp is unrelated if you are not using vscode.

[FlsPrpht]

I am not using VS Code but the full Visual Studio IDE so that linked issue is perhaps unrelated, but the symptom is the same. Perhaps the analyzer needs a better message to describe how to fix the problem no matter what causes it?

[huoyaoyuan]

Perhaps the analyzer needs a better message to describe how to fix the problem no matter what causes it?

There is a chance that the generator hasn't been invoked at all.

To better diagnose this, you may collect: whether this reproduces on command line build, the msbuild binlog, and whether Project->Dependencies->Analyzers in Visual Studio shows Microsoft.Interop.LibraryImportGenerator.

[FlsPrpht]

I can provide the list of analyzers here

What level of verboseness should I enable to see more on the command line than what I am seeing in VS? I can see the same error messages when I run dotnet build.

[huoyaoyuan]

I don't have more ideas about this. The statement is very simple and unlikely to cause the generator to crash or get rejected by it, assuming you are not seeing an AD0001/SYSLIB warning. The generator ships inbox with SDK and is unlikely to be misconfigured. The internal behavior of roslyn isn't visible from msbuild logs.

Usually expanding the Microsoft.Interop.LibraryInteropGenerator you will see generated source and be able to view it. Since it's failing for you, you should be seeing nothing.

[FlsPrpht]

Oh interesting, I never would have thought to expand that and look for warnings/generated code there! Thank you! I am indeed seeing SYSLIB errors but I am also seeing generated code as well.

Here is the generated code. You can see right off the bat, the first warning about using LibraryImportAttribubte instead of DllImportAttribute is accurate (the generated code is using DllImport)

internal static unsafe partial class NativeMethods
{
[global::System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.Interop.LibraryImportGenerator", "8.0.10.31311")]
[global::System.Runtime.CompilerServices.SkipLocalsInitAttribute]
internal static partial bool IsIconic(nint hwnd)
{
bool __retVal;
int __retVal_native;
{
__retVal_native = __PInvoke(hwnd);
}
// Unmarshal - Convert native data to managed data.
__retVal = __retVal_native != 0;
return __retVal;
// Local P/Invoke
[global::System.Runtime.InteropServices.DllImportAttribute("user32.dll", EntryPoint = "IsIconic", ExactSpelling = true)]
static extern unsafe int __PInvoke(nint __hwnd_native);
}
}

[huoyaoyuan]

I am indeed seeing SYSLIB errors but I am also seeing generated code as well.

Those are the warning IDs that the generator/analyzer is capable to produce (it registers to roslyn). If you they produce any warnings, you will see them together with other code warning/errors.

So the generator is able to generate corresponding code, but for some reason the definition and generated parts aren't recognized and matched together.

[jasonmalinowski]

@FlsPrpht If you're seeing the same errors in dotnet build, then run dotnet build /bl and share the log. That either means the generator isn't running, or your code isn't correct in the first place.

[FlsPrpht]

@jasonmalinowski Hi Jason, thank you for the reply. Can I send the log to your email account directly? I was unable to reproduce this in a newly created trivial project and don't want to share details about my project to the larger internet world.

When I run exactly dotnet build /bl I see the exact same error message (and some C++ errors unrelated to this issue).

C:\git<redacted>\NativeMethods.cs(24,41): error CS8795: Partial method 'NativeMethods.IsIconic(n
int)' must have an implementation part because it has accessibility modifiers. [C:\git<redacted>.csproj]

I can send the more detailed log with detailed logs to your email address if that would be helpful.