Fix S1939 FP: Issue is raised when a class derives from another class and declares interface implemention

[mary-georgiou-sonarsource]

Description

An FP is raised when a class is implementing a class and an interface - when the interface is not yet implemented by the class.

Repro steps

  class Foo { }

  interface IBar
  {
      int Test();
  }

  class Bar : Foo, IBar { } // Error [CS0535]
  // Noncompliant@-1 {{'Foo' implements 'IBar' so 'IBar' can be removed from the inheritance list.}}

Expected behavior

An issue should not be raised as Foo is not implementing IBar

Known workarounds

Implementing the interface in IBar in Foo stops raising the issue.

Related information

• C#/VB.NET 8.53

[bottle2]

I just upgraded to 7.2.0.76209, the issue is still going

[arketec]

I have just also experienced the exact same issue with System.Text.Json.JsonConverter on a custom serializer that also implements an interface:

public interface IEnumConverter
{
    protected static readonly Dictionary<string, MyCustomEnum> conversions =
        new()
        {
           // default implementaion
        };
}

 public class MyEnumListConverter
     : System.Text.Json.Serialization.JsonConverter<List<MyCustomEnum>>,
         IEnumConverter
 {
    public override List<MyCustomEnum> Read(
     ref Utf8JsonReader reader,
     Type typeToConvert,
     JsonSerializerOptions options
    ) {
      if (reader.TokenType != JsonTokenType.StartArray)
      {
          throw new System.Text.Json.JsonException();
       }
    
      List<MyCustomEnum> list = new List<MyCustomEnum>();
    
      reader.Read();
      while (reader.TokenType != JsonTokenType.EndArray)
      {
          var val = reader.GetString();
          if (
              val != default
              && IEnumConverter.conversions.ContainsKey(val) // here it references the default implementation of the interface
          )
              list.Add(IEnumConverter.conversions[val]);
      
          reader.Read();
      }
      return list;
    }
 }

currently suppressing with System.Diagnostics.CodeAnalysis.SuppressMessage