Fix missing code generation output for custom data annotation attributes

* Fixes missing code generation output for custom data annotation attributes.
* Adds regression tests.

The two regression tests currently skip the assembly build process, because the two custom data annotation attributes do not exist in the generated assembly. If necessary, the `Microsoft.EntityFrameworkCore.Design.Tests` assembly could be added as a reference or additional source code files (containing the attributes) could be added to the build process.

Fixes #25156

src/EFCore.Design/Scaffolding/Internal/CSharpEntityTypeGenerator.cs

@@ -151,6 +151,8 @@ protected virtual void GenerateEntityTypeDataAnnotations([NotNull] IEntityType e
                 {
                     attributeWriter.AddParameter(_code.UnknownLiteral(argument));
                 }
+
+                _sb.AppendLine(attributeWriter.ToString());
             }
         }
 
@@ -300,6 +302,8 @@ protected virtual void GeneratePropertyDataAnnotations([NotNull] IProperty prope
                 {
                     attributeWriter.AddParameter(_code.UnknownLiteral(argument));
                 }
+
+                _sb.AppendLine(attributeWriter.ToString());
             }
         }
 

test/EFCore.Design.Tests/Scaffolding/Internal/CSharpEntityTypeGeneratorTest.cs

@@ -1,8 +1,17 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System;
+using System.Collections.Generic;
 using System.Linq;
+using Microsoft.EntityFrameworkCore.Design;
+using Microsoft.EntityFrameworkCore.Infrastructure;
 using Microsoft.EntityFrameworkCore.Internal;
+using Microsoft.EntityFrameworkCore.Metadata;
+using Microsoft.EntityFrameworkCore.SqlServer.Design.Internal;
+using Microsoft.EntityFrameworkCore.SqlServer.Metadata.Internal;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.DependencyInjection.Extensions;
 using Xunit;
 
 namespace Microsoft.EntityFrameworkCore.Scaffolding.Internal
@@ -1402,5 +1411,269 @@ public partial class Post
                     Assert.Equal("OriginalPosts", originalInverseNavigation.Name);
                 });
         }
+
+        [ConditionalFact]
+        public void Entity_with_custom_annotation()
+        {
+            Test(
+                modelBuilder => modelBuilder
+                    .Entity(
+                        "EntityWithAnnotation",
+                        x =>
+                        {
+                            x.HasAnnotation("Custom:EntityAnnotation", "first argument");
+                            x.Property<int>("Id");
+                            x.HasKey("Id");
+                        }),
+                new ModelCodeGenerationOptions { UseDataAnnotations = true },
+                code =>
+                {
+                    AssertFileContents(
+                        @"using System;
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+using Microsoft.EntityFrameworkCore;
+
+namespace TestNamespace
+{
+    [CustomEntityDataAnnotation(""first argument"")]
+    public partial class EntityWithAnnotation
+    {
+        [Key]
+        public int Id { get; set; }
+    }
+}
+",
+                        code.AdditionalFiles.Single(f => f.Path == "EntityWithAnnotation.cs"));
+
+                    AssertFileContents(
+                        @"using System;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata;
+
+namespace TestNamespace
+{
+    public partial class TestDbContext : DbContext
+    {
+        public TestDbContext()
+        {
+        }
+
+        public TestDbContext(DbContextOptions<TestDbContext> options)
+            : base(options)
+        {
+        }
+
+        public virtual DbSet<EntityWithAnnotation> EntityWithAnnotation { get; set; }
+
+        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
+        {
+            if (!optionsBuilder.IsConfigured)
+            {
+#warning "
+                        + DesignStrings.SensitiveInformationWarning
+                        + @"
+                optionsBuilder.UseSqlServer(""Initial Catalog=TestDatabase"");
+            }
+        }
+
+        protected override void OnModelCreating(ModelBuilder modelBuilder)
+        {
+            modelBuilder.Entity<EntityWithAnnotation>(entity =>
+            {
+                entity.Property(e => e.Id).UseIdentityColumn();
+            });
+
+            OnModelCreatingPartial(modelBuilder);
+        }
+
+        partial void OnModelCreatingPartial(ModelBuilder modelBuilder);
+    }
+}
+",
+                        code.ContextFile);
+                },
+                assertModel: null,
+                skipBuild: true);
+        }
+
+        [ConditionalFact]
+        public void Entity_property_with_custom_annotation()
+        {
+            Test(
+                modelBuilder => modelBuilder
+                    .Entity(
+                        "EntityWithPropertyAnnotation",
+                        x =>
+                        {
+                            x.Property<int>("Id")
+                                .HasAnnotation("Custom:PropertyAnnotation", "first argument");
+                            x.HasKey("Id");
+                        }),
+                new ModelCodeGenerationOptions { UseDataAnnotations = true },
+                code =>
+                {
+                    AssertFileContents(
+                        @"using System;
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+using Microsoft.EntityFrameworkCore;
+
+namespace TestNamespace
+{
+    public partial class EntityWithPropertyAnnotation
+    {
+        [Key]
+        [CustomPropertyDataAnnotation(""first argument"")]
+        public int Id { get; set; }
+    }
+}
+",
+                        code.AdditionalFiles.Single(f => f.Path == "EntityWithPropertyAnnotation.cs"));
+
+                    AssertFileContents(
+                        @"using System;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata;
+
+namespace TestNamespace
+{
+    public partial class TestDbContext : DbContext
+    {
+        public TestDbContext()
+        {
+        }
+
+        public TestDbContext(DbContextOptions<TestDbContext> options)
+            : base(options)
+        {
+        }
+
+        public virtual DbSet<EntityWithPropertyAnnotation> EntityWithPropertyAnnotation { get; set; }
+
+        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
+        {
+            if (!optionsBuilder.IsConfigured)
+            {
+#warning "
+                        + DesignStrings.SensitiveInformationWarning
+                        + @"
+                optionsBuilder.UseSqlServer(""Initial Catalog=TestDatabase"");
+            }
+        }
+
+        protected override void OnModelCreating(ModelBuilder modelBuilder)
+        {
+            modelBuilder.Entity<EntityWithPropertyAnnotation>(entity =>
+            {
+                entity.Property(e => e.Id).UseIdentityColumn();
+            });
+
+            OnModelCreatingPartial(modelBuilder);
+        }
+
+        partial void OnModelCreatingPartial(ModelBuilder modelBuilder);
+    }
+}
+",
+                        code.ContextFile);
+                },
+                assertModel: null,
+                skipBuild: true);
+        }
+
+        protected override void AddModelServices(IServiceCollection services)
+        {
+            services.Replace(ServiceDescriptor.Singleton<IRelationalAnnotationProvider, ModelAnnotationProvider>());
+        }
+
+        protected override void AddScaffoldingServices(IServiceCollection services)
+        {
+            services.Replace(ServiceDescriptor.Singleton<IAnnotationCodeGenerator, ModelAnnotationCodeGenerator>());
+        }
+
+        public class ModelAnnotationProvider : SqlServerAnnotationProvider
+        {
+            public ModelAnnotationProvider(RelationalAnnotationProviderDependencies dependencies)
+                : base(dependencies)
+            {
+            }
+
+            /// <inheritdoc />
+            public override IEnumerable<IAnnotation> For(ITable table)
+            {
+                foreach (var annotation in base.For(table))
+                {
+                    yield return annotation;
+                }
+
+                var entityType = table.EntityTypeMappings.First().EntityType;
+
+                foreach (var annotation in entityType.GetAnnotations().Where(a => a.Name == "Custom:EntityAnnotation"))
+                {
+                    yield return annotation;
+                }
+            }
+
+            /// <inheritdoc />
+            public override IEnumerable<IAnnotation> For(IColumn column)
+            {
+                foreach (var annotation in base.For(column))
+                {
+                    yield return annotation;
+                }
+
+                var properties = column.PropertyMappings.Select(m => m.Property);
+                var annotations = properties.SelectMany(p => p.GetAnnotations()).GroupBy(a => a.Name).Select(g => g.First());
+
+                foreach (var annotation in annotations.Where(a => a.Name == "Custom:PropertyAnnotation"))
+                {
+                    yield return annotation;
+                }
+            }
+        }
+
+        public class ModelAnnotationCodeGenerator : SqlServerAnnotationCodeGenerator
+        {
+            public ModelAnnotationCodeGenerator(AnnotationCodeGeneratorDependencies dependencies)
+                : base(dependencies)
+            {
+            }
+
+            protected override AttributeCodeFragment GenerateDataAnnotation(IEntityType entityType, IAnnotation annotation)
+                => annotation.Name switch
+                {
+                    "Custom:EntityAnnotation" => new AttributeCodeFragment(
+                        typeof(CustomEntityDataAnnotationAttribute), new object[] { annotation.Value as string }),
+                    _ => base.GenerateDataAnnotation(entityType, annotation)
+                };
+
+            protected override AttributeCodeFragment GenerateDataAnnotation(IProperty property, IAnnotation annotation)
+                => annotation.Name switch
+                {
+                    "Custom:PropertyAnnotation" => new AttributeCodeFragment(typeof(CustomPropertyDataAnnotationAttribute), new object[] {annotation.Value as string}),
+                    _ => base.GenerateDataAnnotation(property, annotation)
+                };
+        }
+
+        [AttributeUsage(AttributeTargets.Class)]
+        public class CustomEntityDataAnnotationAttribute : Attribute
+        {
+            public CustomEntityDataAnnotationAttribute(string argument)
+                => Argument = argument;
+
+            public virtual string Argument { get; }
+        }
+
+        [AttributeUsage(AttributeTargets.Property | AttributeTargets.Field)]
+        public class CustomPropertyDataAnnotationAttribute : Attribute
+        {
+            public CustomPropertyDataAnnotationAttribute(string argument)
+                => Argument = argument;
+
+            public virtual string Argument { get; }
+        }
     }
 }

test/EFCore.Design.Tests/Scaffolding/Internal/ModelCodeGeneratorTestBase.cs

@@ -20,17 +20,23 @@ protected void Test(
             Action<ModelBuilder> buildModel,
             ModelCodeGenerationOptions options,
             Action<ScaffoldedModel> assertScaffold,
-            Action<IModel> assertModel)
+            Action<IModel> assertModel,
+            bool skipBuild = false)
         {
-            var modelBuilder = SqlServerTestHelpers.Instance.CreateConventionBuilder(skipValidation: true);
+            var designServices = new ServiceCollection();
+            AddModelServices(designServices);
+
+            var modelBuilder = SqlServerTestHelpers.Instance.CreateConventionBuilder(skipValidation: true, customServices: designServices);
             modelBuilder.Model.RemoveAnnotation(CoreAnnotationNames.ProductVersion);
             buildModel(modelBuilder);
             var _ = modelBuilder.Model.GetEntityTypeErrors();
 
             var model = modelBuilder.FinalizeModel();
 
-            var services = new ServiceCollection()
-                .AddEntityFrameworkDesignTimeServices();
+            var services = new ServiceCollection();
+            AddScaffoldingServices(services);
+
+            services.AddEntityFrameworkDesignTimeServices();
             new SqlServerDesignTimeServices().ConfigureDesignTimeServices(services);
 
             var generator = services
@@ -60,16 +66,27 @@ protected void Test(
                         scaffoldedModel.AdditionalFiles.Select(f => f.Code)))
             };
 
-            var assembly = build.BuildInMemory();
-            var context = (DbContext)assembly.CreateInstance("TestNamespace.TestDbContext");
-
-            if (assertModel != null)
+            if (!skipBuild)
             {
-                var compiledModel = context.Model;
-                assertModel(compiledModel);
+                var assembly = build.BuildInMemory();
+                var context = (DbContext)assembly.CreateInstance("TestNamespace.TestDbContext");
+
+                if (assertModel != null)
+                {
+                    var compiledModel = context.Model;
+                    assertModel(compiledModel);
+                }
             }
         }
 
+        protected virtual void AddModelServices(IServiceCollection services)
+        {
+        }
+
+        protected virtual void AddScaffoldingServices(IServiceCollection services)
+        {
+        }
+
         protected static void AssertFileContents(
             string expectedCode,
             ScaffoldedFile file)

test/EFCore.Specification.Tests/TestUtilities/TestHelpers.cs

@@ -135,9 +135,13 @@ public IMutableModel BuildModelFor<TEntity>()
             return builder.Model;
         }
 
-        public ModelBuilder CreateConventionBuilder(bool skipValidation = false)
+        public ModelBuilder CreateConventionBuilder(
+            bool skipValidation = false,
+            IServiceCollection customServices = null)
         {
-            var conventionSet = CreateConventionSetBuilder().CreateConventionSet();
+            customServices ??= new ServiceCollection();
+            var contextServices = CreateContextServices(customServices);
+            var conventionSet = contextServices.GetRequiredService<IConventionSetBuilder>().CreateConventionSet();
 
             if (skipValidation)
             {