CA2000 emitted when await using (false positive)

[DrGriff]

Analyzer package

Microsoft.CodeAnalysis.FxCopAnalyzers

Package Version

v2.9.7 (Latest)

Diagnostic ID

Example: CA2000

Repro steps

1. .Net Core 3.1 (latest preview). I happen to be using Blazor Server.
2. Create a Service class that accepts a DbContextOptions
3. Instantate a DbContext in a method. Use the "await using..." C#8 syntax

public class MyService
{
	public DocTypesService(DbContextOptions<MyDbContext> options)
	{
		this.options = options;
	}

	private readonly DbContextOptions<MyDbContext> options;

	public async Task<Something> GetSomethingAsync(string id, CancellationToken token)
	{
		await using var context = new DocTypesContext(this.options);
			....
	}
}

Expected behavior

await using var context = new DocTypesContext(this.options);

The context is created with a using statement, and will be disposed of when it goes out of scope and so no CA2000 error should not be emitted.

Actual behavior

await using var context = new DocTypesContext(this.options);

A CA2000 error is emitted.

However, were we to drop the await command using var context = new DocTypesContext(this.options); then the error is not emitted, but we really do need to put the await in.

[mscrivo]

Seeing the same behaviour after updating to VS 2019 16.4. No way to fix, other than suppress the issue.

[Kharos]

Same here. For teams like ours who use code analysis and warnings as errors (we consider both "best practice"), this means that our existing solution is no longer building after upgrading Visual Studio. Not really a great way of introducing a new .net release 🐞

Edit: Some quick tests show that the error only seems to happen when using a class that inherits from a class that implements IDisposable and IAsyncDisposable. When the used class directly implements IDisposable and IAsyncDisposable, the analyzer works as expected.

[DrGriff]

Similarly to @Kharos, we're also setting all warnings to Errors when compiling in Release mode.

It is a bit naff having to wrap the "offending" lines with pragma warning disable comments.

#pragma warning disable CA2000 // Dispose objects before losing scope. Justification: False positive, see #3042
await using var context = new MyContext(this.options);
#pragma warning restore CA2000 // Dispose objects before losing scope

[mavasani]

#3098 should fix this.

[mavasani]

Fixed with #3098. I will post the beta package that you can try out to verify in a bit.

[mavasani]

https://dotnet.myget.org/feed/roslyn-analyzers/package/nuget/Microsoft.CodeAnalysis.FxCopAnalyzers/2.9.9-beta1.19610.1+906398e7 should have the fix.

[DenSmoke]

https://dotnet.myget.org/feed/roslyn-analyzers/package/nuget/Microsoft.CodeAnalysis.FxCopAnalyzers/2.9.9-beta1.19610.1+906398e7 should have the fix.

When will the fix be available in release build? This issue is really annoying.

[Yanal-Yves]

@DenSmoke, I have Just upgraded my project to "Microsoft.CodeAnalysis.FxCopAnalyzers" Version="3.0.0" and I don't have the issue anymore.

[GeeWee]

I still have it on 3.3.0 with the following code

await using var newMemoryStream = new MemoryStream();

[TaffarelJr]

I'm getting the false positives on MemoryStream as well as GZipStream.

I'm using <EnableNETAnalyzers>true</EnableNETAnalyzers> instead of FxCop, in a library targeting .NET Standard 2.1.

[daviddunson]

Please re-open this bug. I'm using VS 17.0.6 and experiencing the same problem with this code:

var lockStream = new FileStream(lockPath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);

await using (lockStream.ConfigureAwait(false))
{
}

"new FileStream" triggers CA2000.

[cytoph]

Yeah, the issue still exists. Please re-open this bug! It's super annoying that such a common feature is not handled correctly by the analyzers.