PR feedback - add test and fix an instance of != null to is not null

src/libraries/System.Text.Json/gen/JsonSourceGenerator.Emitter.cs

@@ -838,7 +838,7 @@ private void GenerateFastPathFuncForObject(SourceWriter writer, ContextGeneratio
                     switch (defaultCheckType)
                     {
                         case SerializedValueCheckType.IgnoreWhenNull:
-                            writer.WriteLine($"if ({propValueExpr} != null)");
+                            writer.WriteLine($"if ({propValueExpr} is not null)");
                             writer.WriteLine('{');
                             writer.Indentation++;
 

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Unit.Tests/JsonSourceGeneratorTests.cs

@@ -573,6 +573,42 @@ internal partial class JsonContext : JsonSerializerContext
             result.AssertContainsType("int");
         }
 
+        [Fact]
+        public static void NoErrorsWhenUsingTypesWithMultipleEqualsOperators()
+        {
+            // Types that override equals operators used to cause the generated to
+            // emit 'Error CS0034 : Operator '==' is ambiguous on operands of type 'Foo' and '<null>''
+            // This has been changed to use `is null` and `is not null` to disambiguate.
+            string source = """
+                using System.Text.Json.Serialization;
+
+                namespace Test
+                {
+                    public class Foo
+                    {
+                        public override bool Equals(object obj) => false;
+
+                        public static bool operator ==(Foo left, Foo right) => false;
+                        public static bool operator !=(Foo left, Foo right) => false;
+
+                        public static bool operator ==(Foo left, string right) => false;
+                        public static bool operator !=(Foo left, string right) => false;
+
+                        public override int GetHashCode() => 1;
+                    }
+
+                    [JsonSourceGenerationOptions(WriteIndented = true)]
+                    [JsonSerializable(typeof(Foo))]
+                    internal partial class JsonSourceGenerationContext : JsonSerializerContext
+                    {
+                    }
+                }
+                """;
+
+            Compilation compilation = CompilationHelper.CreateCompilation(source);
+            CompilationHelper.RunJsonSourceGenerator(compilation);
+        }
+
         [Fact]
         public static void NoErrorsWhenUsingIgnoredReservedCSharpKeywords()
         {