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.