Added support for hot reload (#71)

Fixes #4

samples/RazorSlices.Samples.WebApp/RazorSlices.Samples.WebApp.csproj

@@ -9,6 +9,8 @@
 
   <PropertyGroup>
     <PublishAot>true</PublishAot>
+    <!-- Startup hooks are disabled when publishing aot/trimmed but are required for Hot Reload to work so enabling it here -->
+    <StartupHookSupport Condition="'$(Configuration)' == 'Debug'">true</StartupHookSupport>
     <!--<PublishTrimmed>true</PublishTrimmed>-->
     <!--<PublishSingleFile>true</PublishSingleFile>-->
     <EnableRequestDelegateGenerator>true</EnableRequestDelegateGenerator>

src/RazorSlices/HotReloadService.cs

@@ -0,0 +1,51 @@
+using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
+using System.Reflection;
+using System.Reflection.Metadata;
+using System.Runtime.CompilerServices;
+
+[assembly: MetadataUpdateHandler(typeof(RazorSlices.HotReloadService))]
+
+namespace RazorSlices;
+
+/// <summary>
+/// A service that provides hot reload functionality for Razor Slices.
+/// See https://learn.microsoft.com/dotnet/api/system.reflection.metadata.metadataupdatehandlerattribute for more information.
+/// </summary>
+internal sealed class HotReloadService
+{
+    public static event Action<Type[]?>? ClearCacheEvent;
+    public static event Action<Type[]?>? UpdateApplicationEvent;
+
+    public static void ClearCache(Type[]? changedTypes)
+    {
+        Debug.WriteLine($"{nameof(HotReloadService)}.{nameof(ClearCache)} invoked with {changedTypes?.Length ?? 0} changed types.");
+        ClearCacheEvent?.Invoke(changedTypes);
+    }
+
+    public static void UpdateApplication(Type[]? changedTypes)
+    {
+        Debug.WriteLine($"{nameof(HotReloadService)}.{nameof(UpdateApplication)} invoked with {changedTypes?.Length ?? 0} changed types.");
+        UpdateApplicationEvent?.Invoke(changedTypes);
+    }
+
+    public static bool TryGetUpdatedType(Type[]? changedTypes, Type originalType, [NotNullWhen(true)] out Type? updatedType)
+    {
+        if (changedTypes is not null)
+        {
+            foreach (var type in changedTypes)
+            {
+                var originalTypeAttribute = type.GetCustomAttribute<MetadataUpdateOriginalTypeAttribute>();
+                if (originalTypeAttribute?.OriginalType == originalType)
+                {
+                    updatedType = type;
+                    Debug.WriteLine($"Type '{originalType.Name}' was replaced with type '{updatedType.Name}' by Hot Reload");
+                    return true;
+                }
+            }
+        }
+
+        updatedType = null;
+        return false;
+    }
+}

src/RazorSlices/SliceDefinition.cs

@@ -1,4 +1,5 @@
-using System.Diagnostics.CodeAnalysis;
+using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Reflection;
 
 namespace RazorSlices;
@@ -11,6 +12,8 @@ namespace RazorSlices;
 /// </remarks>
 public class SliceDefinition
 {
+    private readonly Type _originalSliceType;
+
     /// <summary>
     /// Creates a new instance of <see cref="SliceDefinition"/>.
     /// </summary>
@@ -22,6 +25,18 @@ public SliceDefinition(
     {
         ArgumentNullException.ThrowIfNull(sliceType);
 
+        HotReloadService.ClearCacheEvent += ReplaceSliceType;
+
+        _originalSliceType = sliceType;
+        Initialize(sliceType);
+        Factory = RazorSliceFactory.GetSliceFactory(this);
+    }
+
+    [MemberNotNull(nameof(SliceType))]
+    private void Initialize(
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
+        Type sliceType)
+    {
         SliceType = sliceType;
         HasModel = RazorSliceFactory.IsModelSlice(SliceType);
         ModelProperty = SliceType.GetProperty("Model");
@@ -30,36 +45,50 @@ public SliceDefinition(
         Factory = RazorSliceFactory.GetSliceFactory(this);
     }
 
+    private void ReplaceSliceType(Type[]? changedTypes)
+    {
+        var started = Stopwatch.GetTimestamp();
+
+        if (HotReloadService.TryGetUpdatedType(changedTypes, _originalSliceType, out var updatedSliceType))
+        {
+            Debug.Write($"Hot reloading slice of type '{_originalSliceType.Name}'... ");
+
+            Initialize(updatedSliceType);
+
+            Debug.WriteLine($"done! It took {Stopwatch.GetElapsedTime(started).TotalMilliseconds}ms");
+        }
+    }
+
     /// <summary>
     /// Gets the type of the slice.
     /// </summary>
     [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
-    public Type SliceType { get; }
+    public Type SliceType { get; private set; }
 
     /// <summary>
     /// Gets whether this slice has a model.
     /// </summary>
-    public bool HasModel { get; }
+    public bool HasModel { get; private set; }
 
     /// <summary>
     /// Gets the information about the model property for the slice if it has a model.
     /// </summary>
-    public PropertyInfo? ModelProperty { get; }
+    public PropertyInfo? ModelProperty { get; private set; }
 
     /// <summary>
     /// Gets the model type for the slice if it has a model.
     /// </summary>
-    public Type? ModelType { get; }
+    public Type? ModelType { get; private set; }
 
     /// <summary>
     /// Gets details of the injectable properties for the slice.
     /// </summary>
-    public (bool Any, PropertyInfo[] Nullable, PropertyInfo[] NonNullable) InjectableProperties { get; }
+    public (bool Any, PropertyInfo[] Nullable, PropertyInfo[] NonNullable) InjectableProperties { get; private set; }
 
     /// <summary>
     /// Gets the factory delegate for creating instances of the slice.
     /// </summary>
-    public Delegate Factory { get; }
+    public Delegate Factory { get; private set; }
 
     /// <summary>
     /// Creates a new instance of the slice this definition represents.

tests/RazorSlices.Samples.WebApp.PublishTests/PublishSample.cs

@@ -7,13 +7,14 @@ public class PublishSample
     const string ProjectName = "RazorSlices.Samples.WebApp";
 
     [Theory]
-    [InlineData(PublishScenario.Default)]
+    [InlineData(PublishScenario.Default, "net8.0")]
+    [InlineData(PublishScenario.Default, "net9.0")]
     //[InlineData(PublishScenario.Trimmed)]
     //[InlineData(PublishScenario.AOT)]
-    public void Publish(PublishScenario publishScenario)
+    public void Publish(PublishScenario publishScenario, string tfm)
     {
         var projectBuilder = new ProjectBuilder(ProjectName, publishScenario);
-        projectBuilder.Publish("net8.0");
+        projectBuilder.Publish(tfm);
 
         Assert.DoesNotContain("warning", projectBuilder.PublishResult?.Output, StringComparison.OrdinalIgnoreCase);
     }