[8.0] Request Backport for #91980

[AliveDevil]

Description

Blocked by .NET 8 failing on setting acl on long paths (#91980)

Please backport this as mentioned here #92460 (comment), or provide out-of-band System.IO.FileSystem.AccessControl.dll as consumable NuGet package.

Reproduction Steps

See description.

Expected behavior

See description.

Actual behavior

See description.

Regression?

No response

Known Workarounds

No response

Configuration

No response

Other information

No response

[adamsitnik]

Blocked by .NET 8 failing on setting acl on long paths

Could you please describe your scenario with a more detail (I need strong business justification to justify backporting)? Thanks!

[AliveDevil]

Currently in the process of migrating a codebase from .NET framework to .NET 8 due to .NET Framework not handling long paths correctly.

When .NET 8 doesn’t support long paths like this, there’s no point in going forward, as the next possible LTS version is 10 at the end of 2025.

Scenario is a file synchronization tool, which sets Acls on files, based on remote attributes.

As a workaround I’ve used reflection and a lambdaexpression to get access to the Persist(string) overload, to call that directly with the \\?\-prefix.

Business reason: this is a bug in a core LTS library, that is supported for several years. I‘d understand it, if there’s a newer LTS library available, but STS 9 isn’t even released yet, and 8 is the current LTS, while the mentioned PR was merged before 8 got released. This should’ve been fixed by the .NET 8.0.0 release in Nov 2023. I shouldn’t have to resort to reflection to workaround a core bug.

[jeffhandley]

@AliveDevil We are still deliberating whether to backport this fix to .NET 8. We do think it can be backported, but before we proceed with merging it into a .NET 8 Servicing release, we'd appreciate getting confirmation from you that the fix as included in .NET 9 GA addresses your issue?

Can you try targeting .NET 9 with your repro scenario and confirm that the issue is addressed in .NET 9 and that your scenario works as expected? Thank you in advance.

[AliveDevil]

I can confirm, that the issue is resolved in .NET 9.
As mentioned earlier: We are using the reflection/lambda approach to access the constructor, to pass prefixed paths to Persist():

public static class FileSystemAclExtensions
{
    private static Action<FileSystemSecurity, string> persist;

    public static void PersistUnsafe(this FileSystemSecurity security, string path)
    {
        persist ??= GeneratePersistAccessor();
        persist(security, PathInternal.EnsureExtendedPrefixIfNeeded(Path.GetFullPath(path)));
    }

    private static Action<FileSystemSecurity, string> GeneratePersistAccessor()
    {
        // Workaround for https://github.com/dotnet/runtime/issues/91980
        // Remove with .NET 10
        var type = typeof(FileSystemSecurity);
        var method = type.GetMethod("Persist", BindingFlags.Instance | BindingFlags.NonPublic, [typeof(string)]);

        var instanceParameter = Expression.Parameter(type);
        var persistPathParameter = Expression.Parameter(typeof(string));

        return Expression.Lambda<Action<FileSystemSecurity, string>>(
            Expression.Call(instanceParameter, method, persistPathParameter),
            instanceParameter, persistPathParameter
        ).Compile();
    }
}

[adamsitnik]

Fixed with #113801