Suppress CS1591 warnings in ComInterfaceGenerator generated code (#120104)

Author: Copilot

src/libraries/System.Runtime.InteropServices/gen/ComInterfaceGenerator/ComInterfaceGenerator.cs

@@ -204,7 +204,7 @@ public void Initialize(IncrementalGeneratorInitializationContext context)
 
                     using StringWriter source = new();
                     source.WriteLine("// <auto-generated />");
-                    source.WriteLine("#pragma warning disable CS0612, CS0618, CS0649"); // Suppress warnings about [Obsolete] and "lack of assignment" in generated code.
+                    source.WriteLine("#pragma warning disable CS0612, CS0618, CS0649, CS1591"); // Suppress warnings about [Obsolete], "lack of assignment", and missing XML documentation in generated code.
 
                     // If the user has specified 'ManagedObjectWrapper', it means that the COM interface will never be used to marshal a native
                     // object as an RCW (eg. the IDIC vtable will also not be generated, nor any additional supporting code). To reduce binary

src/libraries/System.Runtime.InteropServices/tests/ComInterfaceGenerator.Unit.Tests/Compiles.cs

@@ -4,8 +4,12 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Linq;
 using System.Runtime.CompilerServices;
 using System.Threading.Tasks;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.Testing;
 using Microsoft.Interop.UnitTests;
 using Xunit;
 using VerifyComInterfaceGenerator = Microsoft.Interop.UnitTests.Verifiers.CSharpSourceGeneratorVerifier<Microsoft.Interop.ComInterfaceGenerator>;
@@ -369,5 +373,80 @@ public async Task ValidateComInterfaceSnippets(string id, string source)
 
             await VerifyComInterfaceGenerator.VerifySourceGeneratorAsync(source);
         }
+
+        [Fact]
+        public async Task DocumentedComInterfaceDoesNotProduceCS1591Warnings()
+        {
+            string source = """
+                using System.Runtime.InteropServices;
+                using System.Runtime.InteropServices.Marshalling;
+
+                namespace Test
+                {
+                    /// <summary>
+                    /// This is my interface.
+                    /// </summary>
+                    [GeneratedComInterface, Guid("27dd3a3d-4c16-485a-a123-7cd8f39c6ef2")]
+                    public partial interface IMyInterface
+                    {
+                        /// <summary>
+                        /// This does something.
+                        /// </summary>
+                        void DoSomething();
+                    }
+
+                    /// <summary>
+                    /// This is my other interface.
+                    /// </summary>
+                    [GeneratedComInterface, Guid("1b681178-368a-4d13-8893-66b4673d2ff9")]
+                    public partial interface MyOtherInterface : IMyInterface
+                    {
+                        /// <summary>
+                        /// This does something else.
+                        /// </summary>
+                        void DoSomethingElse();
+                    }
+                }
+                """;
+
+            var test = new VerifyCompilationTest<Microsoft.Interop.ComInterfaceGenerator>(false)
+            {
+                TestCode = source,
+                TestBehaviors = TestBehaviors.SkipGeneratedSourcesCheck | TestBehaviors.SkipGeneratedCodeCheck,
+                CompilationVerifier = compilation =>
+                {
+                    // Verify that no CS1591 warnings are produced in the generated code
+                    var diagnostics = compilation.GetDiagnostics();
+                    var cs1591Diagnostics = diagnostics.Where(d => d.Id == "CS1591").ToList();
+                    
+                    Assert.Empty(cs1591Diagnostics);
+                }
+            };
+            
+            // Enable XML documentation warnings to ensure CS1591 would be raised if not suppressed
+            test.SolutionTransforms.Add((solution, projectId) =>
+            {
+                var project = solution.GetProject(projectId);
+                if (project is null) return solution;
+                
+                // Set parse options to enable documentation mode which is required for CS1591 validation
+                var parseOptions = (CSharpParseOptions?)project.ParseOptions;
+                if (parseOptions is not null)
+                {
+                    parseOptions = parseOptions.WithDocumentationMode(DocumentationMode.Diagnose);
+                    solution = solution.WithProjectParseOptions(projectId, parseOptions);
+                    project = solution.GetProject(projectId)!;
+                }
+                
+                var compilationOptions = project.CompilationOptions!
+                    .WithSpecificDiagnosticOptions(new Dictionary<string, ReportDiagnostic>
+                    {
+                        ["CS1591"] = ReportDiagnostic.Warn
+                    });
+                return solution.WithProjectCompilationOptions(projectId, compilationOptions);
+            });
+
+            await test.RunAsync();
+        }
     }
 }