Don't use reflection for part creation

gen/DocumentFormat.OpenXml.Generator.Models/Models/SchemaType.cs

@@ -11,6 +11,8 @@ public class SchemaType
 
     public bool IsPart => !string.IsNullOrEmpty(Part);
 
+    public bool IsRootElement => IsPart || BaseClass == "OpenXmlPartRootElement" || BaseClass == "OpenXmlPartRootElement";
+
     public string Part { get; set; } = null!;
 
     public ParticleOrderType CompositeType { get; set; }

gen/DocumentFormat.OpenXml.Generator/FactoryGenerator.cs

@@ -0,0 +1,135 @@
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using DocumentFormat.OpenXml.Generator.Editor;
+using DocumentFormat.OpenXml.Generator.Generators.Parts;
+using Microsoft.CodeAnalysis;
+using System.CodeDom.Compiler;
+using System.Text;
+
+namespace DocumentFormat.OpenXml.Generator;
+
+[Generator]
+public class FactoryGenerator : IIncrementalGenerator
+{
+    public void Initialize(IncrementalGeneratorInitializationContext context)
+    {
+        var openXml = context.GetOpenXmlGeneratorContext()
+            .GetOpenXmlServices();
+
+        context.RegisterSourceOutput(openXml, (context, openXml) =>
+        {
+            GeneratePartFactory(context, openXml);
+            GenerateRootActivator(context, openXml);
+        });
+    }
+
+    private static void GeneratePartFactory(SourceProductionContext context, OpenXmlGeneratorServices openXml)
+    {
+        using var sw = new StringWriter();
+        using var writer = new IndentedTextWriter(sw);
+
+        writer.WriteFileHeader();
+
+        writer.WriteLine("using DocumentFormat.OpenXml;");
+        writer.WriteLine("using DocumentFormat.OpenXml.Packaging;");
+        writer.WriteLine();
+        writer.WriteLine("namespace DocumentFormat.OpenXml.Features;");
+
+        writer.WriteLine("internal partial class TypedPartFactory : IPartFactory");
+
+        using (writer.AddBlock())
+        {
+            writer.WriteLine("public T? Create<T>() where T : OpenXmlPart");
+
+            using (writer.AddBlock())
+            {
+                foreach (var part in openXml.Context.Parts)
+                {
+                    writer.Write("if (typeof(T) == typeof(");
+                    writer.Write(part.Name);
+                    writer.WriteLine("))");
+
+                    using (writer.AddBlock())
+                    {
+                        writer.Write("return (T)(object)new ");
+                        writer.Write(part.Name);
+                        writer.WriteLine("();");
+                    }
+
+                    writer.WriteLine();
+                }
+
+                writer.WriteLine("return default;");
+            }
+        }
+
+        context.AddSource("TypedPartFactory", sw.ToString());
+    }
+
+    private static void GenerateRootActivator(SourceProductionContext context, OpenXmlGeneratorServices openXml)
+    {
+        using var sw = new StringWriter();
+        using var writer = new IndentedTextWriter(sw);
+
+        writer.WriteFileHeader();
+
+        writer.WriteLine("using System;");
+        writer.WriteLine("using System.Collections.Generic;");
+        writer.WriteLine("using DocumentFormat.OpenXml;");
+        writer.WriteLine("using DocumentFormat.OpenXml.Packaging;");
+        writer.WriteLine("using DocumentFormat.OpenXml.Framework.Metadata;");
+        writer.WriteLine();
+        writer.WriteLine("namespace DocumentFormat.OpenXml.Features;");
+
+        writer.WriteLine("internal partial class TypedRootElementFactory : IRootElementFactory");
+
+        using (writer.AddBlock())
+        {
+            writer.WriteLine("public static IEnumerable<ElementFactory> GetAllRootElements()");
+
+            using (writer.AddBlock())
+            {
+                foreach (var model in openXml.Context.Namespaces)
+                {
+                    foreach (var type in model.Types)
+                    {
+                        if (type.IsRootElement)
+                        {
+                            var className = openXml.FindClassName(type.Name, fullyQualified: true);
+
+                            writer.Write("yield return new ElementFactory(typeof(");
+                            writer.Write(className);
+                            writer.Write("), new(");
+                            writer.WriteString(openXml.GetNamespaceInfo(type.Name.QName.Prefix).Uri);
+                            writer.Write(", ");
+                            writer.WriteString(type.Name.QName.Name);
+                            writer.Write("), () => new ");
+                            writer.Write(className);
+                            writer.WriteLine("());");
+                        }
+                    }
+                }
+            }
+        }
+
+        context.AddSource("TypedRootFactory", sw.ToString());
+    }
+
+    private static void WritePartFiles(SourceProductionContext context, OpenXmlGeneratorServices openXml)
+    {
+        var sb = new StringBuilder();
+        var sw = new StringWriter(sb);
+        var writer = new IndentedTextWriter(sw);
+
+        foreach (var part in openXml.Context.Parts)
+        {
+            sb.Clear();
+
+            writer.WriteFileHeader();
+            writer.WritePart(openXml, part);
+
+            context.AddSource(part.Name, sb.ToString());
+        }
+    }
+}

gen/DocumentFormat.OpenXml.Generator/PartGenerator.cs

@@ -16,28 +16,35 @@ public void Initialize(IncrementalGeneratorInitializationContext context)
     {
         var openXml = context.GetOpenXmlGeneratorContext().GetOpenXmlServices();
         var options = context.GetOpenXmlOptions().Select(static (o, _) => o.GenerateParts);
+        var parts = openXml.Combine(options);
 
-        context.RegisterSourceOutput(openXml.Combine(options), (context, data) =>
+        context.RegisterSourceOutput(parts, (context, data) =>
         {
             if (!data.Right)
             {
                 return;
             }
 
             var openXml = data.Left;
-            var sb = new StringBuilder();
-            var sw = new StringWriter(sb);
-            var writer = new IndentedTextWriter(sw);
 
-            foreach (var part in openXml.Context.Parts)
-            {
-                sb.Clear();
+            WritePartFiles(context, openXml);
+        });
+    }
 
-                writer.WriteFileHeader();
-                writer.WritePart(openXml, part);
+    private static void WritePartFiles(SourceProductionContext context, OpenXmlGeneratorServices openXml)
+    {
+        var sb = new StringBuilder();
+        var sw = new StringWriter(sb);
+        var writer = new IndentedTextWriter(sw);
 
-                context.AddSource(part.Name, sb.ToString());
-            }
-        });
+        foreach (var part in openXml.Context.Parts)
+        {
+            sb.Clear();
+
+            writer.WriteFileHeader();
+            writer.WritePart(openXml, part);
+
+            context.AddSource(part.Name, sb.ToString());
+        }
     }
 }

src/DocumentFormat.OpenXml/Features/IPartFactory.cs

@@ -7,5 +7,5 @@ namespace DocumentFormat.OpenXml.Features;
 
 internal interface IPartFactory
 {
-    T Create<T>() where T : OpenXmlPart;
+    T? Create<T>() where T : OpenXmlPart;
 }

src/DocumentFormat.OpenXml/Features/TypedFeatures.cs

@@ -29,10 +29,10 @@ public static IFeatureCollection Shared
 
     public int Revision => 0;
 
-    [KnownFeature(typeof(IRootElementFactory), typeof(ReflectionBasedRootElementFactory))]
+    [KnownFeature(typeof(IRootElementFactory), typeof(TypedRootElementFactory))]
     [KnownFeature(typeof(IPartMetadataFeature), typeof(CachedPartMetadataProvider))]
     [KnownFeature(typeof(IOpenXmlNamespaceResolver), typeof(OpenXmlNamespaceResolver))]
-    [KnownFeature(typeof(IPartFactory), typeof(ReflectionPartFactory))]
+    [KnownFeature(typeof(IPartFactory), typeof(TypedPartFactory))]
     [DelegatedFeature(nameof(FeatureCollection.Default), typeof(FeatureCollection))]
     [ThreadSafe]
     public partial T? Get<T>();

src/DocumentFormat.OpenXml/Features/TypedRootElementFactory.cs

@@ -0,0 +1,27 @@
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using DocumentFormat.OpenXml.Framework;
+using DocumentFormat.OpenXml.Framework.Metadata;
+using System;
+using System.Diagnostics.CodeAnalysis;
+
+namespace DocumentFormat.OpenXml.Features;
+
+internal partial class TypedRootElementFactory : IRootElementFactory
+{
+    private readonly Lazy<ElementFactoryCollection> _collection;
+
+    public TypedRootElementFactory()
+    {
+        _collection = new Lazy<ElementFactoryCollection>(() => new ElementFactoryCollection(GetAllRootElements()));
+    }
+
+    public ElementFactoryCollection Collection => _collection.Value;
+
+    public bool TryCreate(in OpenXmlQualifiedName qname, [NotNullWhen(true)] out OpenXmlElement? element)
+    {
+        element = _collection.Value.Create(in qname);
+        return element is not null;
+    }
+}

src/DocumentFormat.OpenXml/Packaging/OpenXmlPartContainer.cs

@@ -1077,9 +1077,13 @@ internal T AddNewPartInternal<T>()
         {
             ThrowIfObjectDisposed();
 
-            // use reflection to create the instance. As the default constructor of part is not "public"
             var part = Features.GetRequired<IPartFactory>().Create<T>();
 
+            if (part is null)
+            {
+                throw new OpenXmlPackageException(ExceptionMessages.AddedPartIsNotAllowed);
+            }
+
             try
             {
                 InitPart(part, part.ContentType);
@@ -1145,6 +1149,11 @@ internal T AddNewPartInternal<T>(string? contentType, string? id)
                 throw new ArgumentOutOfRangeException(nameof(T), ExceptionMessages.ExtendedPartNotAllowed);
             }
 
+            if (part is null)
+            {
+                throw new OpenXmlPackageException(ExceptionMessages.AddedPartIsNotAllowed);
+            }
+
             if (contentType is not null && part.IsContentTypeFixed && !string.Equals(contentType, part.ContentType, StringComparison.Ordinal))
             {
                 throw new ArgumentOutOfRangeException(nameof(contentType), ExceptionMessages.ErrorContentType);