Implement hot reload support with cache clearing and registry reset

README.md

@@ -114,6 +114,7 @@ Mark computed properties and methods with `[Expressive]` to generate companion e
 | Tuples, index/range, `with`, collection expressions | And more modern C# syntax |
 | Expression transformers | Built-in + custom `IExpressionTreeTransformer` pipeline |
 | SQL window functions | ROW_NUMBER, RANK, DENSE_RANK, NTILE, PERCENT_RANK, CUME_DIST, SUM/AVG/COUNT/MIN/MAX OVER, LAG/LEAD, FIRST_VALUE/LAST_VALUE/NTH_VALUE with ROWS/RANGE frames (experimental) |
+| Hot reload | Compatible with `dotnet watch` — edits to `[Expressive]` bodies propagate to generated expression trees |
 
 See the [full documentation](https://efnext.github.io/ExpressiveSharp/guide/introduction) for detailed usage, [reference](https://efnext.github.io/ExpressiveSharp/reference/expressive-attribute), and [recipes](https://efnext.github.io/ExpressiveSharp/recipes/computed-properties).
 

src/ExpressiveSharp.Generator/Registry/ExpressionRegistryEmitter.cs

@@ -145,12 +145,15 @@ private static void WriteRegistryEntryStatement(IndentedTextWriter writer, Expre
     }
 
     /// <summary>
-    /// Emits the <c>_map</c> field that lazily builds the registry once at class-load time:
-    /// <c>private static readonly Dictionary&lt;nint, LambdaExpression&gt; _map = Build();</c>
+    /// Emits the <c>_map</c> field plus a <c>ResetMap</c> entry point used by the hot-reload
+    /// handler to rebuild the map after a metadata update has patched the factory-method IL.
+    /// Not <c>readonly</c> — the handler reassigns it.
     /// </summary>
     private static void EmitMapField(IndentedTextWriter writer)
     {
-        writer.WriteLine("private static readonly Dictionary<nint, LambdaExpression> _map = Build();");
+        writer.WriteLine("private static Dictionary<nint, LambdaExpression> _map = Build();");
+        writer.WriteLine();
+        writer.WriteLine("internal static void ResetMap() => _map = Build();");
     }
 
     /// <summary>

src/ExpressiveSharp/Services/ExpressiveHotReloadHandler.cs

@@ -0,0 +1,48 @@
+using System;
+using System.Reflection;
+using System.Reflection.Metadata;
+
+[assembly: MetadataUpdateHandler(typeof(ExpressiveSharp.Services.ExpressiveHotReloadHandler))]
+
+namespace ExpressiveSharp.Services;
+
+internal static class ExpressiveHotReloadHandler
+{
+    public static void ClearCache(Type[]? updatedTypes)
+    {
+        ResetGeneratedRegistries();
+        ExpressiveResolver.ClearCachesForMetadataUpdate();
+        ExpressiveReplacer.ClearCachesForMetadataUpdate();
+    }
+
+    public static void UpdateApplication(Type[]? updatedTypes) => ClearCache(updatedTypes);
+
+    /// <summary>
+    /// Finds every loaded assembly's generated <c>ExpressiveSharp.Generated.ExpressionRegistry</c>
+    /// class and invokes its <c>ResetMap()</c> method so the next <c>TryGet</c> rebuilds
+    /// <c>LambdaExpression</c> instances from the hot-reloaded factory IL.
+    /// </summary>
+    private static void ResetGeneratedRegistries()
+    {
+        foreach (var assembly in AppDomain.CurrentDomain.GetAssemblies())
+        {
+            if (assembly.IsDynamic) continue;
+
+            Type? registryType;
+            try
+            {
+                registryType = assembly.GetType("ExpressiveSharp.Generated.ExpressionRegistry", throwOnError: false);
+            }
+            catch
+            {
+                continue;
+            }
+
+            var reset = registryType?.GetMethod("ResetMap", BindingFlags.Static | BindingFlags.NonPublic);
+            if (reset is null) continue;
+
+            try { reset.Invoke(null, null); }
+            catch { /* best-effort; stale registry stays stale */ }
+        }
+    }
+}

src/ExpressiveSharp/Services/ExpressiveReplacer.cs

@@ -21,6 +21,8 @@ public class ExpressiveReplacer : ExpressionVisitor
 
     private static readonly ConditionalWeakTable<Type, StrongBox<bool>> _compilerGeneratedClosureCache = new();
 
+    internal static void ClearCachesForMetadataUpdate() => _compilerGeneratedClosureCache.Clear();
+
     public ExpressiveReplacer(IExpressiveResolver resolver)
     {
         _resolver = resolver;

src/ExpressiveSharp/Services/ExpressiveResolver.cs

@@ -35,6 +35,24 @@ internal static void ResetAllCaches()
             _assemblyScanFilter = null;
         }
 
+        /// <summary>
+        /// Invalidates cached expression trees so the next lookup rebuilds from the (possibly
+        /// hot-reloaded) generated factory method. Called from <see cref="ExpressiveHotReloadHandler"/>.
+        /// Preserves <c>_assemblyScanFilter</c> and <c>_typeNameCache</c> — neither goes stale on
+        /// non-rude edits, and wiping the filter would silently disable a user-configured restriction.
+        /// </summary>
+        internal static void ClearCachesForMetadataUpdate()
+        {
+            _expressionCache.Clear();
+            _reflectionCache.Clear();
+            _assemblyRegistries.Clear();
+            Volatile.Write(ref _lastScannedAssemblyCount, 0);
+        }
+
+        internal static bool IsExpressionCached(MemberInfo mi) => _expressionCache.ContainsKey(mi);
+
+        internal static Func<Assembly, bool>? GetAssemblyScanFilter() => _assemblyScanFilter;
+
         private static Func<Assembly, bool>? _assemblyScanFilter;
 
         /// <summary>

tests/ExpressiveSharp.Generator.Tests/ExpressiveGenerator/RegistryTests.MethodOverloads_BothRegistered.verified.txt

@@ -22,7 +22,9 @@ namespace ExpressiveSharp.Generated
             return map;
         }
 
-        private static readonly Dictionary<nint, LambdaExpression> _map = Build();
+        private static Dictionary<nint, LambdaExpression> _map = Build();
+
+        internal static void ResetMap() => _map = Build();
 
         public static LambdaExpression TryGet(MemberInfo member)
         {

tests/ExpressiveSharp.Generator.Tests/ExpressiveGenerator/RegistryTests.MultipleExpressives_AllRegistered.verified.txt

@@ -22,7 +22,9 @@ namespace ExpressiveSharp.Generated
             return map;
         }
 
-        private static readonly Dictionary<nint, LambdaExpression> _map = Build();
+        private static Dictionary<nint, LambdaExpression> _map = Build();
+
+        internal static void ResetMap() => _map = Build();
 
         public static LambdaExpression TryGet(MemberInfo member)
         {

tests/ExpressiveSharp.Generator.Tests/ExpressiveGenerator/RegistryTests.SingleMethod_RegistryContainsEntry.verified.txt

@@ -21,7 +21,9 @@ namespace ExpressiveSharp.Generated
             return map;
         }
 
-        private static readonly Dictionary<nint, LambdaExpression> _map = Build();
+        private static Dictionary<nint, LambdaExpression> _map = Build();
+
+        internal static void ResetMap() => _map = Build();
 
         public static LambdaExpression TryGet(MemberInfo member)
         {

tests/ExpressiveSharp.Generator.Tests/ExpressiveGenerator/RegistryTests.SingleProperty_RegistryContainsEntry.verified.txt

@@ -21,7 +21,9 @@ namespace ExpressiveSharp.Generated
             return map;
         }
 
-        private static readonly Dictionary<nint, LambdaExpression> _map = Build();
+        private static Dictionary<nint, LambdaExpression> _map = Build();
+
+        internal static void ResetMap() => _map = Build();
 
         public static LambdaExpression TryGet(MemberInfo member)
         {

tests/ExpressiveSharp.Tests/Services/ExpressiveHotReloadHandlerTests.cs

@@ -0,0 +1,81 @@
+using System.Reflection;
+using System.Reflection.Metadata;
+using ExpressiveSharp.Services;
+using ExpressiveSharp.Tests.TestFixtures;
+
+namespace ExpressiveSharp.Tests.Services;
+
+[TestClass]
+public class ExpressiveHotReloadHandlerTests
+{
+    [TestMethod]
+    public void ClearCache_AfterResolve_RemovesMemberFromCache()
+    {
+        var mi = typeof(Product).GetProperty(nameof(Product.Total))!;
+        var resolver = new ExpressiveResolver();
+
+        _ = resolver.FindGeneratedExpression(mi);
+        Assert.IsTrue(ExpressiveResolver.IsExpressionCached(mi));
+
+        ExpressiveHotReloadHandler.ClearCache(null);
+
+        Assert.IsFalse(ExpressiveResolver.IsExpressionCached(mi));
+    }
+
+    [TestMethod]
+    public void ClearCache_PreservesAssemblyScanFilter()
+    {
+        var sentinel = new Func<Assembly, bool>(_ => true);
+        ExpressiveResolver.SetAssemblyScanFilter(sentinel);
+        try
+        {
+            ExpressiveHotReloadHandler.ClearCache(null);
+
+            Assert.AreSame(sentinel, ExpressiveResolver.GetAssemblyScanFilter());
+        }
+        finally
+        {
+            ExpressiveResolver.SetAssemblyScanFilter(null);
+        }
+    }
+
+    [TestMethod]
+    public void ClearCache_RebuildReturnsEquivalentExpression()
+    {
+        var mi = typeof(Product).GetProperty(nameof(Product.Total))!;
+        var resolver = new ExpressiveResolver();
+
+        var before = resolver.FindGeneratedExpression(mi).ToString();
+
+        ExpressiveHotReloadHandler.ClearCache(null);
+
+        var after = resolver.FindGeneratedExpression(mi).ToString();
+
+        Assert.AreEqual(before, after);
+    }
+
+    [TestMethod]
+    public void ClearCache_WithNullAndEmptyAndPopulatedArrays_DoesNotThrow()
+    {
+        ExpressiveHotReloadHandler.ClearCache(null);
+        ExpressiveHotReloadHandler.ClearCache([]);
+        ExpressiveHotReloadHandler.ClearCache([typeof(Product)]);
+    }
+
+    [TestMethod]
+    public void UpdateApplication_WithNull_DoesNotThrow()
+    {
+        ExpressiveHotReloadHandler.UpdateApplication(null);
+    }
+
+    [TestMethod]
+    public void Assembly_RegistersExpressiveHotReloadHandler()
+    {
+        var attributes = typeof(ExpressiveResolver).Assembly
+            .GetCustomAttributes<MetadataUpdateHandlerAttribute>()
+            .ToList();
+
+        Assert.IsTrue(attributes.Any(a => a.HandlerType == typeof(ExpressiveHotReloadHandler)),
+            "MetadataUpdateHandlerAttribute for ExpressiveHotReloadHandler not found on ExpressiveSharp assembly.");
+    }
+}