Fix S3604 FP: Primary constructors

[hankovich]

Description

S3604 is reported for classes with primary constructors.

Repro steps

class SampleClass(object options)
{
    private readonly object _options = options; // Noncompliant - FP: S3604 shouldn't be reported here, this is not a redundant initializer
}

Expected behavior

S3064 should not be raised.

Actual behavior

S3064 raises a warning.

Known workarounds

N/A

Related information

• C#/VB.NET Plugins version: 9.5.0.73987
• Visual Studio version: latest preview
• MSBuild / dotnet version: .NET 8 preview 6

[zsolt-kolbay-sonarsource]

Thank you for reporting this issue @hankovich. Confirmed as False Positive.

[smokedlinq]

With .NET 8.0 right around the corner, this would be nice to get fixed as the primary constructor refactor causes this to appear

[OpenEnergyGroup]

This is an issue for properties too: this code will raises an incorrect S3604 warning:

public class Foo(string foo)
{
    public List<string> MyList { get; } = [foo];
}

Thanks.

[Guiorgy]

.NET 8 is out, and indeed I get S3604:

public sealed class MyClass(string name, string lastName) : IEquatable<MyClass>
{
    public string Name { get; } = name; // S3604
    public string LastName{ get; } = lastName; // S3604
    // ...
}

As a workaround, you could rewrite the properties to return the generated private field dirrectly instead of the backing fields:

public sealed class MyClass(string name, string lastName) : IEquatable<MyClass>
{
    public string Name { get => name; }
    public string LastName{ get; } = lastName; // S3604
    // ...
}

Name no longer triggers S3604. Here's the Generated C#:

[System.Runtime.CompilerServices.NullableContext(1)]
[System.Runtime.CompilerServices.Nullable(0)]
public sealed class MyClass
{
    [CompilerGenerated]
    [DebuggerBrowsable(DebuggerBrowsableState.Never)]
    private string <name>P;

    [CompilerGenerated]
    [DebuggerBrowsable(DebuggerBrowsableState.Never)]
    private readonly string <LastName>k__BackingField;

    public string Name
    {
        get
        {
            return <name>P;
        }
    }

    public string LastName
    {
        [CompilerGenerated]
        get
        {
            return <LastName>k__BackingField;
        }
    }

    public MyClass(string name, string lastName)
    {
        <name>P = name;
        <LastName>k__BackingField = lastName;
        base..ctor();
    }
}

So pretty much the same.

[Corniel]

I can confirm this issue.

[Davidsv]

Still got this issue, NET 8.0.100, latest visal studio 17.8, latest sonarlint 7.4.0.80741

[FelixDamrau]

.NET 8 is out, and indeed I get S3604:
...snip...
As a workaround, you could rewrite the properties to return the generated private field dirrectly instead of the backing fields:
...snip...
So pretty much the same.

The workaround suppresses the S3604 message, but the compiler-generated backing field is not readonly anymore.

Thank you for your effort in providing the workaround. However, I still need the readonly stuff, so this issue remains a concern for me.

Anyhow, I mainly want to add a comment, so this issue may get prioritized.

[Guiorgy]

You're right, missed that. readonly should allow the runtime some low level optimizations too

[shkarface]

The issue has affected our codebases as we're upgrading to .NET 8 and new C# features as well.

+1.

[ms-lemos]

+1.
False positives with .net 8. Commenting in hope for this to get priority, it's quite annoying.

[andrei-epure-sonarsource]

Thanks, we will prioritize it and apologies for missing this in our previous release.

[Corniel]

Thanks, we will prioritize it and apologies for missing this in our previous release.

Those things can happen. No worries. Are you considering to ship it earlier than you normally do?

[andrei-epure-sonarsource]

@Corniel, it went into the latest release. Soon, we'll deploy to nuget.org, and next week, we'll deploy to SonarCloud.
This will be included in SQ 10.4 and the next release of SonarLint.

Thanks to all who reported this issue on this thread, and again, my apologies for slipping this through the cracks.

[Corniel]

We're all developers, we all miss things sometimes. No reason to apologize. Keep up the good work!