[release/10.0] Suppress warnings in JSON source generated code

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

@@ -137,16 +137,27 @@ private static SourceWriter CreateSourceWriterWithContextHeader(ContextGeneratio
             {
                 var writer = new SourceWriter();
 
+                // In release builds of the generator, we suppress all diagnostics stemming from the generated code.
+                // There's nothing a developer can do about these diagnostics, and they can break the build. In debug
+                // builds, we allow more warnings in order to catch potential issues early.
+#if DEBUG
                 writer.WriteLine("""
                     // <auto-generated/>
 
                     #nullable enable annotations
                     #nullable disable warnings
+                    #pragma warning disable CS0612, CS0618 // [Obsolete] member usage
 
-                    // Suppress warnings about [Obsolete] member usage in generated code.
-                    #pragma warning disable CS0612, CS0618
+                    """);
+#else
+                writer.WriteLine("""
+                    // <auto-generated/>
+
+                    #nullable enable annotations
+                    #pragma warning disable
 
                     """);
+#endif
 
                 if (contextSpec.Namespace != null)
                 {

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

@@ -184,6 +184,16 @@ internal sealed class CompilerFeatureRequiredAttribute : Attribute
                     public CompilerFeatureRequiredAttribute(string featureName) { }
                 }
             }
+
+            namespace System.Diagnostics.CodeAnalysis
+            {
+                internal sealed class ExperimentalAttribute : Attribute
+                {
+                    public ExperimentalAttribute(string diagnosticId) => DiagnosticId = diagnosticId;
+                    public string DiagnosticId { get; }
+                    public string UrlFormat { get; set; }
+                }
+            }
             """;
 #endif
 

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

@@ -521,6 +521,36 @@ public class ClassWithObsolete
             CompilationHelper.RunJsonSourceGenerator(compilation);
         }
 
+        [Fact]
+        public static void NoWarningsDueToExperimentalMembers()
+        {
+            string source = """
+                using System;
+                using System.Diagnostics.CodeAnalysis;
+                using System.Text.Json.Serialization;
+
+                namespace Test
+                {
+                #pragma warning disable TEST001
+                    [JsonSerializable(typeof(ClassWithExperimental))]
+                #pragma warning restore TEST001
+                    public partial class JsonContext : JsonSerializerContext { }
+
+                    public class ClassWithExperimental
+                    {
+                        [Experimental("TEST001")]
+                        public bool Test { get; set; }
+
+                        [Experimental("TEST002")]
+                        public bool Test2 { get; set; }
+                    }
+                }
+                """;
+
+            Compilation compilation = CompilationHelper.CreateCompilation(source);
+            CompilationHelper.RunJsonSourceGenerator(compilation);
+        }
+
         [Fact]
         public static void NoErrorsWhenUsingReservedCSharpKeywords()
         {