[hot_reload] implement param reflection

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/ReflectionAddNewMethod.cs

@@ -0,0 +1,16 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+using System;
+
+
+namespace System.Reflection.Metadata.ApplyUpdate.Test
+{
+ public class ReflectionAddNewMethod
+ {
+ public string ExistingMethod(string u, double f)
+	{
+ return u + f.ToString();;
+ }
+
+ }
+}

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/ReflectionAddNewMethod_v1.cs

@@ -0,0 +1,21 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+using System;
+using System.Runtime.CompilerServices;
+using CancellationToken = System.Threading.CancellationToken;
+
+namespace System.Reflection.Metadata.ApplyUpdate.Test
+{
+ public class ReflectionAddNewMethod
+ {
+ public string ExistingMethod(string u, double f)
+	{
+ return u + f.ToString();;
+ }
+
+	public double AddedNewMethod(char c, float h, string w, CancellationToken ct = default, [CallerMemberName] string callerName = "")
+	{
+ return ((double)Convert.ToInt32(c)) + h;
+	}
+ }
+}

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod.csproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+ <PropertyGroup>
+ <RootNamespace>System.Runtime.Loader.Tests</RootNamespace>
+ <TargetFramework>$(NetCoreAppCurrent)</TargetFramework>
+ <TestRuntime>true</TestRuntime>
+ <DeltaScript>deltascript.json</DeltaScript>
+ </PropertyGroup>
+ <ItemGroup>
+ <Compile Include="ReflectionAddNewMethod.cs" />
+ </ItemGroup>
+</Project>

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/deltascript.json

@@ -0,0 +1,6 @@
+{
+ "changes": [
+ {"document": "ReflectionAddNewMethod.cs", "update": "ReflectionAddNewMethod_v1.cs"},
+ ]
+}
+

src/libraries/System.Runtime.Loader/tests/ApplyUpdateTest.cs

@@ -3,6 +3,7 @@
 
 using System.Reflection;
 using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
 using Xunit;
 
 namespace System.Reflection.Metadata
@@ -629,5 +630,87 @@ public static void TestReflectionAddNewType()
  System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewType.ZExistingClass.ExistingMethod ();
  });
  }
+
+ [ConditionalFact(typeof(ApplyUpdateUtil), nameof(ApplyUpdateUtil.IsSupported))]
+ public static void TestReflectionAddNewMethod()
+ {
+ ApplyUpdateUtil.TestCase(static () =>
+ {
+ var ty = typeof(System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod);
+ var assm = ty.Assembly;
+
+ var bindingFlags = BindingFlags.Instance | BindingFlags.Public;
+ var allMethods = ty.GetMethods(bindingFlags);
+
+ int objectMethods = typeof(object).GetMethods(bindingFlags).Length;
+ Assert.Equal (objectMethods + 1, allMethods.Length);
+
+ ApplyUpdateUtil.ApplyUpdate(assm);
+ ApplyUpdateUtil.ClearAllReflectionCaches();
+
+ ty = typeof(System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod);
+
+ allMethods = ty.GetMethods(bindingFlags);
+ Assert.Equal (objectMethods + 2, allMethods.Length);
+
+ var mi = ty.GetMethod ("AddedNewMethod");
+
+ Assert.NotNull (mi);
+
+ var retParm = mi.ReturnParameter;
+ Assert.NotNull (retParm);
+ Assert.NotNull (retParm.ParameterType);
+ Assert.Equal (-1, retParm.Position);
+
+ var retCas = retParm.GetCustomAttributes(false);
+ Assert.NotNull(retCas);
+ Assert.Equal(0, retCas.Length);
+
+ var parms = mi.GetParameters();
+ Assert.Equal (5, parms.Length);
+
+ int parmPos = 0;
+ foreach (var parm in parms)
+ {
+ Assert.NotNull(parm);
+ Assert.NotNull(parm.ParameterType);
+ Assert.Equal(parmPos, parm.Position);
+ Assert.NotNull(parm.Name);
+
+ var cas = parm.GetCustomAttributes(false);
+ foreach (var ca in cas) {
+ Assert.NotNull (ca);
+ }
+
+ parmPos++;
+ }
+
+ var parmAttrs = parms[4].GetCustomAttributes(false);
+ Assert.Equal (2, parmAttrs.Length);
+ bool foundCallerMemberName = false;
+ bool foundOptional = false;
+ foreach (var pa in parmAttrs) {
+ if (typeof (CallerMemberNameAttribute).Equals(pa.GetType()))
+ {
+ foundCallerMemberName = true;
+ }
+ if (typeof (OptionalAttribute).Equals(pa.GetType()))
+ {
+ foundOptional = true;
+ }
+ }
+ Assert.True(foundCallerMemberName);
+ Assert.True(foundOptional);
+
+ // n.b. this typeof() also makes the rest of the test work on Wasm with aggressive trimming.
+ Assert.Equal (typeof(System.Threading.CancellationToken), parms[3].ParameterType);
+
+ Assert.True(parms[3].HasDefaultValue);
+ Assert.True(parms[4].HasDefaultValue);
+
+ Assert.Null(parms[3].DefaultValue);
+ Assert.Equal(string.Empty, parms[4].DefaultValue);
+ });
+	} 
  }
 }

src/libraries/System.Runtime.Loader/tests/System.Runtime.Loader.Tests.csproj

@@ -62,6 +62,7 @@
  <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.AddStaticLambda\System.Reflection.Metadata.ApplyUpdate.Test.AddStaticLambda.csproj" />
  <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.StaticLambdaRegression\System.Reflection.Metadata.ApplyUpdate.Test.StaticLambdaRegression.csproj" />
  <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewType\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewType.csproj" />
+ <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod.csproj" />
  </ItemGroup>
  <ItemGroup Condition="'$(TargetOS)' == 'Browser'">
  <WasmFilesToIncludeFromPublishDir Include="$(AssemblyName).dll" />

src/mono/mono/component/hot_reload-internals.h

@@ -86,4 +86,9 @@ typedef struct _MonoClassMetadataUpdateEvent {
 	uint32_t token; /* the Event table token where this event was defined. */
 } MonoClassMetadataUpdateEvent;
 
+typedef struct _MonoMethodMetadataUpdateParamInfo {
+	uint32_t first_param_token; /* a Param token */
+	uint32_t param_count;
+} MonoMethodMetadataUpdateParamInfo;
+
 #endif/*_MONO_COMPONENT_HOT_RELOAD_INTERNALS_H*/

src/mono/mono/component/hot_reload-stub.c

@@ -110,6 +110,9 @@ hot_reload_get_num_methods_added (MonoClass *klass);
 static const char *
 hot_reload_get_capabilities (void);
 
+static uint32_t
+hot_reload_stub_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt);
+
 static MonoComponentHotReload fn_table = {
 	{ MONO_COMPONENT_ITF_VERSION, &hot_reload_stub_available },
 	&hot_reload_stub_set_fastpath_data,
@@ -142,7 +145,8 @@ static MonoComponentHotReload fn_table = {
 	&hot_reload_stub_added_fields_iter,
 	&hot_reload_get_num_fields_added,
 	&hot_reload_get_num_methods_added,
-	&hot_reload_get_capabilities
+	&hot_reload_get_capabilities,
+	&hot_reload_stub_get_method_params,
 };
 
 static bool
@@ -343,6 +347,12 @@ hot_reload_get_capabilities (void)
 	return "";
 }
 
+static uint32_t
+hot_reload_stub_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt)
+{
+	return 0;
+}
+
 MONO_COMPONENT_EXPORT_ENTRYPOINT
 MonoComponentHotReload *
 mono_component_hot_reload_init (void)

src/mono/mono/component/hot_reload.c

@@ -144,6 +144,9 @@ hot_reload_get_num_methods_added (MonoClass *klass);
 static const char *
 hot_reload_get_capabilities (void);
 
+static uint32_t
+hot_reload_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt);
+
 static MonoClassMetadataUpdateField *
 metadata_update_field_setup_basic_info (MonoImage *image_base, BaselineInfo *base_info, uint32_t generation, DeltaInfo *delta_info, MonoClass *parent_klass, uint32_t fielddef_token, uint32_t field_flags);
 
@@ -179,7 +182,8 @@ static MonoComponentHotReload fn_table = {
 	&hot_reload_added_fields_iter,
 	&hot_reload_get_num_fields_added,
 	&hot_reload_get_num_methods_added,
-	&hot_reload_get_capabilities
+	&hot_reload_get_capabilities,
+	&hot_reload_get_method_params,
 };
 
 MonoComponentHotReload *
@@ -272,6 +276,9 @@ struct _BaselineInfo {
 	/* Parents for added methods, fields, etc */
 	GHashTable *member_parent; /* maps added methoddef or fielddef tokens to typedef tokens */
 
+	/* Params for added methods */
+	GHashTable *method_params; /* maps methoddef tokens to a MonoClassMetadataUpdateMethodParamInfo* */
+
 	/* Skeletons for all newly-added types from every generation. Accessing the array requires the image lock. */
 	GArray *skeletons;
 };
@@ -412,6 +419,12 @@ baseline_info_destroy (BaselineInfo *info)
 	if (info->skeletons)
  g_array_free (info->skeletons, TRUE);
 
+	if (info->member_parent)
+ g_hash_table_destroy (info->member_parent);
+
+	if (info->method_params)
+ g_hash_table_destroy (info->method_params);
+
 	g_free (info);
 }
 
@@ -627,6 +640,11 @@ add_method_to_baseline (BaselineInfo *base_info, DeltaInfo *delta_info, MonoClas
 static void
 add_field_to_baseline (BaselineInfo *base_info, DeltaInfo *delta_info, MonoClass *klass, uint32_t field_token);
 
+/* Add a method->params lookup for new methods in existing classes */
+static void
+add_param_info_for_method (BaselineInfo *base_info, uint32_t param_token, uint32_t method_token);
+
+
 void
 hot_reload_init (void)
 {
@@ -2019,6 +2037,7 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
 	uint32_t add_member_typedef = 0;
 	uint32_t add_property_propertymap = 0;
 	uint32_t add_event_eventmap = 0;
+	uint32_t add_field_method = 0;
 
 	gboolean assemblyref_updated = FALSE;
 	for (guint32 i = 0; i < rows ; ++i) {
@@ -2049,6 +2068,7 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
 
  case ENC_FUNC_ADD_PARAM: {
  g_assert (token_table == MONO_TABLE_METHOD);
+ add_field_method = log_token;
  break;
  }
  case ENC_FUNC_ADD_FIELD: {
@@ -2115,8 +2135,11 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
  }
  case MONO_TABLE_METHOD: {
  /* if adding a param, handle it with the next record */
- if (func_code == ENC_FUNC_ADD_PARAM)
+ if (func_code == ENC_FUNC_ADD_PARAM) {
+ g_assert (is_addition);
  break;
+ }
+ g_assert (func_code == ENC_FUNC_DEFAULT);
 
  if (!base_info->method_table_update)
  base_info->method_table_update = g_hash_table_new (g_direct_hash, g_direct_equal);
@@ -2366,9 +2389,21 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
  *
  * So by the time we see the param additions, the methods are already in.
  *
- * FIXME: we need a lookaside table (like member_parent) for every place
- * that looks at MONO_METHOD_PARAMLIST
  */
+ if (is_addition) {
+ g_assert (add_field_method != 0);
+ uint32_t parent_type_token = hot_reload_method_parent (image_base, add_field_method);
+ g_assert (parent_type_token != 0); // we added a parameter to a method that was added
+ if (pass2_context_is_skeleton (ctx, parent_type_token)) {
+ // it's a parameter on a new method in a brand new class
+ // FIXME: need to do something here?
+ } else {
+ // it's a parameter on a new method in an existing class
+ add_param_info_for_method (base_info, log_token, add_field_method);
+ }
+ add_field_method = 0;
+ break;
+ }
  break;
  }
  case MONO_TABLE_INTERFACEIMPL: {
@@ -2819,6 +2854,28 @@ hot_reload_field_parent (MonoImage *base_image, uint32_t field_token)
 }
 
 
+static void
+add_param_info_for_method (BaselineInfo *base_info, uint32_t param_token, uint32_t method_token)
+{
+	if (!base_info->method_params) {
+ base_info->method_params = g_hash_table_new_full (g_direct_hash, g_direct_equal, NULL, g_free);
+	}
+	MonoMethodMetadataUpdateParamInfo* info = NULL;
+	info = g_hash_table_lookup (base_info->method_params, GUINT_TO_POINTER (method_token));
+	if (!info) {
+ // FIXME locking
+ info = g_new0 (MonoMethodMetadataUpdateParamInfo, 1);
+ g_hash_table_insert (base_info->method_params, GUINT_TO_POINTER (method_token), info);
+ info->first_param_token = param_token;
+ info->param_count = 1;
+	} else {
+ uint32_t param_index = mono_metadata_token_index (param_token);
+ // expect params for a single method to be a contiguous sequence of rows
+ g_assert (mono_metadata_token_index (info->first_param_token) + info->param_count == param_index);
+ info->param_count++;
+	}
+}
+
 /* HACK - keep in sync with locator_t in metadata/metadata.c */
 typedef struct {
 	guint32 idx; /* The index that we are trying to locate */
@@ -3148,6 +3205,32 @@ hot_reload_get_num_methods_added (MonoClass *klass)
 	return count;
 }
 
+static uint32_t
+hot_reload_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt)
+{
+	BaselineInfo *base_info = baseline_info_lookup (base_image);
+	g_assert (base_info);
+
+	/* FIXME: locking in case the hash table grows */
+
+	if (!base_info->method_params)
+ return 0;
+
+	MonoMethodMetadataUpdateParamInfo* info = NULL;
+	info = g_hash_table_lookup (base_info->method_params, GUINT_TO_POINTER (methoddef_token));
+	if (!info) {
+ if (out_param_count_opt)
+ *out_param_count_opt = 0;
+ return 0;
+	}
+
+	if (out_param_count_opt)
+ *out_param_count_opt = info->param_count;
+
+	return mono_metadata_token_index (info->first_param_token);
+}
+
+
 static const char *
 hot_reload_get_capabilities (void)
 {

src/mono/mono/component/hot_reload.h

@@ -48,6 +48,7 @@ typedef struct _MonoComponentHotReload {
 	uint32_t (*get_num_fields_added) (MonoClass *klass);
 	uint32_t (*get_num_methods_added) (MonoClass *klass);
 	const char* (*get_capabilities) (void);
+	uint32_t (*get_method_params) (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt);
 } MonoComponentHotReload;
 
 MONO_COMPONENT_EXPORT_ENTRYPOINT

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/ReflectionAddNewMethod.cs

@@ -0,0 +1,16 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+using System;
+
+
+namespace System.Reflection.Metadata.ApplyUpdate.Test
+{
+ public class ReflectionAddNewMethod
+ {
+ public string ExistingMethod(string u, double f)
+	{
+ return u + f.ToString();;
+ }
+
+ }
+}

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/ReflectionAddNewMethod_v1.cs

@@ -0,0 +1,21 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+using System;
+using System.Runtime.CompilerServices;
+using CancellationToken = System.Threading.CancellationToken;
+
+namespace System.Reflection.Metadata.ApplyUpdate.Test
+{
+ public class ReflectionAddNewMethod
+ {
+ public string ExistingMethod(string u, double f)
+	{
+ return u + f.ToString();;
+ }
+
+	public double AddedNewMethod(char c, float h, string w, CancellationToken ct = default, [CallerMemberName] string callerName = "")
+	{
+ return ((double)Convert.ToInt32(c)) + h;
+	}
+ }
+}

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod.csproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+ <PropertyGroup>
+ <RootNamespace>System.Runtime.Loader.Tests</RootNamespace>
+ <TargetFramework>$(NetCoreAppCurrent)</TargetFramework>
+ <TestRuntime>true</TestRuntime>
+ <DeltaScript>deltascript.json</DeltaScript>
+ </PropertyGroup>
+ <ItemGroup>
+ <Compile Include="ReflectionAddNewMethod.cs" />
+ </ItemGroup>
+</Project>

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/deltascript.json

@@ -0,0 +1,6 @@
+{
+ "changes": [
+ {"document": "ReflectionAddNewMethod.cs", "update": "ReflectionAddNewMethod_v1.cs"},
+ ]
+}
+

src/libraries/System.Runtime.Loader/tests/ApplyUpdateTest.cs

@@ -3,6 +3,7 @@
 
 using System.Reflection;
 using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
 using Xunit;
 
 namespace System.Reflection.Metadata
@@ -629,5 +630,87 @@ public static void TestReflectionAddNewType()
  System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewType.ZExistingClass.ExistingMethod ();
  });
  }
+
+ [ConditionalFact(typeof(ApplyUpdateUtil), nameof(ApplyUpdateUtil.IsSupported))]
+ public static void TestReflectionAddNewMethod()
+ {
+ ApplyUpdateUtil.TestCase(static () =>
+ {
+ var ty = typeof(System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod);
+ var assm = ty.Assembly;
+
+ var bindingFlags = BindingFlags.Instance | BindingFlags.Public;
+ var allMethods = ty.GetMethods(bindingFlags);
+
+ int objectMethods = typeof(object).GetMethods(bindingFlags).Length;
+ Assert.Equal (objectMethods + 1, allMethods.Length);
+
+ ApplyUpdateUtil.ApplyUpdate(assm);
+ ApplyUpdateUtil.ClearAllReflectionCaches();
+
+ ty = typeof(System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod);
+
+ allMethods = ty.GetMethods(bindingFlags);
+ Assert.Equal (objectMethods + 2, allMethods.Length);
+
+ var mi = ty.GetMethod ("AddedNewMethod");
+
+ Assert.NotNull (mi);
+
+ var retParm = mi.ReturnParameter;
+ Assert.NotNull (retParm);
+ Assert.NotNull (retParm.ParameterType);
+ Assert.Equal (-1, retParm.Position);
+
+ var retCas = retParm.GetCustomAttributes(false);
+ Assert.NotNull(retCas);
+ Assert.Equal(0, retCas.Length);
+
+ var parms = mi.GetParameters();
+ Assert.Equal (5, parms.Length);
+
+ int parmPos = 0;
+ foreach (var parm in parms)
+ {
+ Assert.NotNull(parm);
+ Assert.NotNull(parm.ParameterType);
+ Assert.Equal(parmPos, parm.Position);
+ Assert.NotNull(parm.Name);
+
+ var cas = parm.GetCustomAttributes(false);
+ foreach (var ca in cas) {
+ Assert.NotNull (ca);
+ }
+
+ parmPos++;
+ }
+
+ var parmAttrs = parms[4].GetCustomAttributes(false);
+ Assert.Equal (2, parmAttrs.Length);
+ bool foundCallerMemberName = false;
+ bool foundOptional = false;
+ foreach (var pa in parmAttrs) {
+ if (typeof (CallerMemberNameAttribute).Equals(pa.GetType()))
+ {
+ foundCallerMemberName = true;
+ }
+ if (typeof (OptionalAttribute).Equals(pa.GetType()))
+ {
+ foundOptional = true;
+ }
+ }
+ Assert.True(foundCallerMemberName);
+ Assert.True(foundOptional);
+
+ // n.b. this typeof() also makes the rest of the test work on Wasm with aggressive trimming.
+ Assert.Equal (typeof(System.Threading.CancellationToken), parms[3].ParameterType);
+
+ Assert.True(parms[3].HasDefaultValue);
+ Assert.True(parms[4].HasDefaultValue);
+
+ Assert.Null(parms[3].DefaultValue);
+ Assert.Equal(string.Empty, parms[4].DefaultValue);
+ });
+	} 
  }
 }

src/libraries/System.Runtime.Loader/tests/System.Runtime.Loader.Tests.csproj

@@ -62,6 +62,7 @@
  <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.AddStaticLambda\System.Reflection.Metadata.ApplyUpdate.Test.AddStaticLambda.csproj" />
  <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.StaticLambdaRegression\System.Reflection.Metadata.ApplyUpdate.Test.StaticLambdaRegression.csproj" />
  <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewType\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewType.csproj" />
+ <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod.csproj" />
  </ItemGroup>
  <ItemGroup Condition="'$(TargetOS)' == 'Browser'">
  <WasmFilesToIncludeFromPublishDir Include="$(AssemblyName).dll" />

src/mono/mono/component/hot_reload-internals.h

@@ -86,4 +86,9 @@ typedef struct _MonoClassMetadataUpdateEvent {
 	uint32_t token; /* the Event table token where this event was defined. */
 } MonoClassMetadataUpdateEvent;
 
+typedef struct _MonoMethodMetadataUpdateParamInfo {
+	uint32_t first_param_token; /* a Param token */
+	uint32_t param_count;
+} MonoMethodMetadataUpdateParamInfo;
+
 #endif/*_MONO_COMPONENT_HOT_RELOAD_INTERNALS_H*/

src/mono/mono/component/hot_reload-stub.c

@@ -110,6 +110,9 @@ hot_reload_get_num_methods_added (MonoClass *klass);
 static const char *
 hot_reload_get_capabilities (void);
 
+static uint32_t
+hot_reload_stub_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt);
+
 static MonoComponentHotReload fn_table = {
 	{ MONO_COMPONENT_ITF_VERSION, &hot_reload_stub_available },
 	&hot_reload_stub_set_fastpath_data,
@@ -142,7 +145,8 @@ static MonoComponentHotReload fn_table = {
 	&hot_reload_stub_added_fields_iter,
 	&hot_reload_get_num_fields_added,
 	&hot_reload_get_num_methods_added,
-	&hot_reload_get_capabilities
+	&hot_reload_get_capabilities,
+	&hot_reload_stub_get_method_params,
 };
 
 static bool
@@ -343,6 +347,12 @@ hot_reload_get_capabilities (void)
 	return "";
 }
 
+static uint32_t
+hot_reload_stub_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt)
+{
+	return 0;
+}
+
 MONO_COMPONENT_EXPORT_ENTRYPOINT
 MonoComponentHotReload *
 mono_component_hot_reload_init (void)

src/mono/mono/component/hot_reload.c

@@ -144,6 +144,9 @@ hot_reload_get_num_methods_added (MonoClass *klass);
 static const char *
 hot_reload_get_capabilities (void);
 
+static uint32_t
+hot_reload_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt);
+
 static MonoClassMetadataUpdateField *
 metadata_update_field_setup_basic_info (MonoImage *image_base, BaselineInfo *base_info, uint32_t generation, DeltaInfo *delta_info, MonoClass *parent_klass, uint32_t fielddef_token, uint32_t field_flags);
 
@@ -179,7 +182,8 @@ static MonoComponentHotReload fn_table = {
 	&hot_reload_added_fields_iter,
 	&hot_reload_get_num_fields_added,
 	&hot_reload_get_num_methods_added,
-	&hot_reload_get_capabilities
+	&hot_reload_get_capabilities,
+	&hot_reload_get_method_params,
 };
 
 MonoComponentHotReload *
@@ -272,6 +276,9 @@ struct _BaselineInfo {
 	/* Parents for added methods, fields, etc */
 	GHashTable *member_parent; /* maps added methoddef or fielddef tokens to typedef tokens */
 
+	/* Params for added methods */
+	GHashTable *method_params; /* maps methoddef tokens to a MonoClassMetadataUpdateMethodParamInfo* */
+
 	/* Skeletons for all newly-added types from every generation. Accessing the array requires the image lock. */
 	GArray *skeletons;
 };
@@ -412,6 +419,12 @@ baseline_info_destroy (BaselineInfo *info)
 	if (info->skeletons)
  g_array_free (info->skeletons, TRUE);
 
+	if (info->member_parent)
+ g_hash_table_destroy (info->member_parent);
+
+	if (info->method_params)
+ g_hash_table_destroy (info->method_params);
+
 	g_free (info);
 }
 
@@ -627,6 +640,11 @@ add_method_to_baseline (BaselineInfo *base_info, DeltaInfo *delta_info, MonoClas
 static void
 add_field_to_baseline (BaselineInfo *base_info, DeltaInfo *delta_info, MonoClass *klass, uint32_t field_token);
 
+/* Add a method->params lookup for new methods in existing classes */
+static void
+add_param_info_for_method (BaselineInfo *base_info, uint32_t param_token, uint32_t method_token);
+
+
 void
 hot_reload_init (void)
 {
@@ -2019,6 +2037,7 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
 	uint32_t add_member_typedef = 0;
 	uint32_t add_property_propertymap = 0;
 	uint32_t add_event_eventmap = 0;
+	uint32_t add_field_method = 0;
 
 	gboolean assemblyref_updated = FALSE;
 	for (guint32 i = 0; i < rows ; ++i) {
@@ -2049,6 +2068,7 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
 
  case ENC_FUNC_ADD_PARAM: {
  g_assert (token_table == MONO_TABLE_METHOD);
+ add_field_method = log_token;
  break;
  }
  case ENC_FUNC_ADD_FIELD: {
@@ -2115,8 +2135,11 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
  }
  case MONO_TABLE_METHOD: {
  /* if adding a param, handle it with the next record */
- if (func_code == ENC_FUNC_ADD_PARAM)
+ if (func_code == ENC_FUNC_ADD_PARAM) {
+ g_assert (is_addition);
  break;
+ }
+ g_assert (func_code == ENC_FUNC_DEFAULT);
 
  if (!base_info->method_table_update)
  base_info->method_table_update = g_hash_table_new (g_direct_hash, g_direct_equal);
@@ -2366,9 +2389,21 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
  *
  * So by the time we see the param additions, the methods are already in.
  *
- * FIXME: we need a lookaside table (like member_parent) for every place
- * that looks at MONO_METHOD_PARAMLIST
  */
+ if (is_addition) {
+ g_assert (add_field_method != 0);
+ uint32_t parent_type_token = hot_reload_method_parent (image_base, add_field_method);
+ g_assert (parent_type_token != 0); // we added a parameter to a method that was added
+ if (pass2_context_is_skeleton (ctx, parent_type_token)) {
+ // it's a parameter on a new method in a brand new class
+ // FIXME: need to do something here?
+ } else {
+ // it's a parameter on a new method in an existing class
+ add_param_info_for_method (base_info, log_token, add_field_method);
+ }
+ add_field_method = 0;
+ break;
+ }
  break;
  }
  case MONO_TABLE_INTERFACEIMPL: {
@@ -2819,6 +2854,28 @@ hot_reload_field_parent (MonoImage *base_image, uint32_t field_token)
 }
 
 
+static void
+add_param_info_for_method (BaselineInfo *base_info, uint32_t param_token, uint32_t method_token)
+{
+	if (!base_info->method_params) {
+ base_info->method_params = g_hash_table_new_full (g_direct_hash, g_direct_equal, NULL, g_free);
+	}
+	MonoMethodMetadataUpdateParamInfo* info = NULL;
+	info = g_hash_table_lookup (base_info->method_params, GUINT_TO_POINTER (method_token));
+	if (!info) {
+ // FIXME locking
+ info = g_new0 (MonoMethodMetadataUpdateParamInfo, 1);
+ g_hash_table_insert (base_info->method_params, GUINT_TO_POINTER (method_token), info);
+ info->first_param_token = param_token;
+ info->param_count = 1;
+	} else {
+ uint32_t param_index = mono_metadata_token_index (param_token);
+ // expect params for a single method to be a contiguous sequence of rows
+ g_assert (mono_metadata_token_index (info->first_param_token) + info->param_count == param_index);
+ info->param_count++;
+	}
+}
+
 /* HACK - keep in sync with locator_t in metadata/metadata.c */
 typedef struct {
 	guint32 idx; /* The index that we are trying to locate */
@@ -3148,6 +3205,32 @@ hot_reload_get_num_methods_added (MonoClass *klass)
 	return count;
 }
 
+static uint32_t
+hot_reload_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt)
+{
+	BaselineInfo *base_info = baseline_info_lookup (base_image);
+	g_assert (base_info);
+
+	/* FIXME: locking in case the hash table grows */
+
+	if (!base_info->method_params)
+ return 0;
+
+	MonoMethodMetadataUpdateParamInfo* info = NULL;
+	info = g_hash_table_lookup (base_info->method_params, GUINT_TO_POINTER (methoddef_token));
+	if (!info) {
+ if (out_param_count_opt)
+ *out_param_count_opt = 0;
+ return 0;
+	}
+
+	if (out_param_count_opt)
+ *out_param_count_opt = info->param_count;
+
+	return mono_metadata_token_index (info->first_param_token);
+}
+
+
 static const char *
 hot_reload_get_capabilities (void)
 {

src/mono/mono/component/hot_reload.h

@@ -48,6 +48,7 @@ typedef struct _MonoComponentHotReload {
 	uint32_t (*get_num_fields_added) (MonoClass *klass);
 	uint32_t (*get_num_methods_added) (MonoClass *klass);
 	const char* (*get_capabilities) (void);
+	uint32_t (*get_method_params) (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt);
 } MonoComponentHotReload;
 
 MONO_COMPONENT_EXPORT_ENTRYPOINT

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/ReflectionAddNewMethod.cs

@@ -0,0 +1,16 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+using System;
+
+
+namespace System.Reflection.Metadata.ApplyUpdate.Test
+{
+ public class ReflectionAddNewMethod
+ {
+ public string ExistingMethod(string u, double f)
+	{
+ return u + f.ToString();;
+ }
+
+ }
+}

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/ReflectionAddNewMethod_v1.cs

@@ -0,0 +1,21 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+using System;
+using System.Runtime.CompilerServices;
+using CancellationToken = System.Threading.CancellationToken;
+
+namespace System.Reflection.Metadata.ApplyUpdate.Test
+{
+ public class ReflectionAddNewMethod
+ {
+ public string ExistingMethod(string u, double f)
+	{
+ return u + f.ToString();;
+ }
+
+	public double AddedNewMethod(char c, float h, string w, CancellationToken ct = default, [CallerMemberName] string callerName = "")
+	{
+ return ((double)Convert.ToInt32(c)) + h;
+	}
+ }
+}

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod.csproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+ <PropertyGroup>
+ <RootNamespace>System.Runtime.Loader.Tests</RootNamespace>
+ <TargetFramework>$(NetCoreAppCurrent)</TargetFramework>
+ <TestRuntime>true</TestRuntime>
+ <DeltaScript>deltascript.json</DeltaScript>
+ </PropertyGroup>
+ <ItemGroup>
+ <Compile Include="ReflectionAddNewMethod.cs" />
+ </ItemGroup>
+</Project>

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/deltascript.json

@@ -0,0 +1,6 @@
+{
+ "changes": [
+ {"document": "ReflectionAddNewMethod.cs", "update": "ReflectionAddNewMethod_v1.cs"},
+ ]
+}
+

src/libraries/System.Runtime.Loader/tests/ApplyUpdateTest.cs

@@ -3,6 +3,7 @@
 
 using System.Reflection;
 using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
 using Xunit;
 
 namespace System.Reflection.Metadata
@@ -629,5 +630,87 @@ public static void TestReflectionAddNewType()
  System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewType.ZExistingClass.ExistingMethod ();
  });
  }
+
+ [ConditionalFact(typeof(ApplyUpdateUtil), nameof(ApplyUpdateUtil.IsSupported))]
+ public static void TestReflectionAddNewMethod()
+ {
+ ApplyUpdateUtil.TestCase(static () =>
+ {
+ var ty = typeof(System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod);
+ var assm = ty.Assembly;
+
+ var bindingFlags = BindingFlags.Instance | BindingFlags.Public;
+ var allMethods = ty.GetMethods(bindingFlags);
+
+ int objectMethods = typeof(object).GetMethods(bindingFlags).Length;
+ Assert.Equal (objectMethods + 1, allMethods.Length);
+
+ ApplyUpdateUtil.ApplyUpdate(assm);
+ ApplyUpdateUtil.ClearAllReflectionCaches();
+
+ ty = typeof(System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod);
+
+ allMethods = ty.GetMethods(bindingFlags);
+ Assert.Equal (objectMethods + 2, allMethods.Length);
+
+ var mi = ty.GetMethod ("AddedNewMethod");
+
+ Assert.NotNull (mi);
+
+ var retParm = mi.ReturnParameter;
+ Assert.NotNull (retParm);
+ Assert.NotNull (retParm.ParameterType);
+ Assert.Equal (-1, retParm.Position);
+
+ var retCas = retParm.GetCustomAttributes(false);
+ Assert.NotNull(retCas);
+ Assert.Equal(0, retCas.Length);
+
+ var parms = mi.GetParameters();
+ Assert.Equal (5, parms.Length);
+
+ int parmPos = 0;
+ foreach (var parm in parms)
+ {
+ Assert.NotNull(parm);
+ Assert.NotNull(parm.ParameterType);
+ Assert.Equal(parmPos, parm.Position);
+ Assert.NotNull(parm.Name);
+
+ var cas = parm.GetCustomAttributes(false);
+ foreach (var ca in cas) {
+ Assert.NotNull (ca);
+ }
+
+ parmPos++;
+ }
+
+ var parmAttrs = parms[4].GetCustomAttributes(false);
+ Assert.Equal (2, parmAttrs.Length);
+ bool foundCallerMemberName = false;
+ bool foundOptional = false;
+ foreach (var pa in parmAttrs) {
+ if (typeof (CallerMemberNameAttribute).Equals(pa.GetType()))
+ {
+ foundCallerMemberName = true;
+ }
+ if (typeof (OptionalAttribute).Equals(pa.GetType()))
+ {
+ foundOptional = true;
+ }
+ }
+ Assert.True(foundCallerMemberName);
+ Assert.True(foundOptional);
+
+ // n.b. this typeof() also makes the rest of the test work on Wasm with aggressive trimming.
+ Assert.Equal (typeof(System.Threading.CancellationToken), parms[3].ParameterType);
+
+ Assert.True(parms[3].HasDefaultValue);
+ Assert.True(parms[4].HasDefaultValue);
+
+ Assert.Null(parms[3].DefaultValue);
+ Assert.Equal(string.Empty, parms[4].DefaultValue);
+ });
+	} 
  }
 }

src/libraries/System.Runtime.Loader/tests/System.Runtime.Loader.Tests.csproj

@@ -62,6 +62,7 @@
  <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.AddStaticLambda\System.Reflection.Metadata.ApplyUpdate.Test.AddStaticLambda.csproj" />
  <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.StaticLambdaRegression\System.Reflection.Metadata.ApplyUpdate.Test.StaticLambdaRegression.csproj" />
  <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewType\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewType.csproj" />
+ <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod.csproj" />
  </ItemGroup>
  <ItemGroup Condition="'$(TargetOS)' == 'Browser'">
  <WasmFilesToIncludeFromPublishDir Include="$(AssemblyName).dll" />

src/mono/mono/component/hot_reload-internals.h

@@ -86,4 +86,9 @@ typedef struct _MonoClassMetadataUpdateEvent {
 	uint32_t token; /* the Event table token where this event was defined. */
 } MonoClassMetadataUpdateEvent;
 
+typedef struct _MonoMethodMetadataUpdateParamInfo {
+	uint32_t first_param_token; /* a Param token */
+	uint32_t param_count;
+} MonoMethodMetadataUpdateParamInfo;
+
 #endif/*_MONO_COMPONENT_HOT_RELOAD_INTERNALS_H*/

src/mono/mono/component/hot_reload-stub.c

@@ -110,6 +110,9 @@ hot_reload_get_num_methods_added (MonoClass *klass);
 static const char *
 hot_reload_get_capabilities (void);
 
+static uint32_t
+hot_reload_stub_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt);
+
 static MonoComponentHotReload fn_table = {
 	{ MONO_COMPONENT_ITF_VERSION, &hot_reload_stub_available },
 	&hot_reload_stub_set_fastpath_data,
@@ -142,7 +145,8 @@ static MonoComponentHotReload fn_table = {
 	&hot_reload_stub_added_fields_iter,
 	&hot_reload_get_num_fields_added,
 	&hot_reload_get_num_methods_added,
-	&hot_reload_get_capabilities
+	&hot_reload_get_capabilities,
+	&hot_reload_stub_get_method_params,
 };
 
 static bool
@@ -343,6 +347,12 @@ hot_reload_get_capabilities (void)
 	return "";
 }
 
+static uint32_t
+hot_reload_stub_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt)
+{
+	return 0;
+}
+
 MONO_COMPONENT_EXPORT_ENTRYPOINT
 MonoComponentHotReload *
 mono_component_hot_reload_init (void)

src/mono/mono/component/hot_reload.c

@@ -144,6 +144,9 @@ hot_reload_get_num_methods_added (MonoClass *klass);
 static const char *
 hot_reload_get_capabilities (void);
 
+static uint32_t
+hot_reload_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt);
+
 static MonoClassMetadataUpdateField *
 metadata_update_field_setup_basic_info (MonoImage *image_base, BaselineInfo *base_info, uint32_t generation, DeltaInfo *delta_info, MonoClass *parent_klass, uint32_t fielddef_token, uint32_t field_flags);
 
@@ -179,7 +182,8 @@ static MonoComponentHotReload fn_table = {
 	&hot_reload_added_fields_iter,
 	&hot_reload_get_num_fields_added,
 	&hot_reload_get_num_methods_added,
-	&hot_reload_get_capabilities
+	&hot_reload_get_capabilities,
+	&hot_reload_get_method_params,
 };
 
 MonoComponentHotReload *
@@ -272,6 +276,9 @@ struct _BaselineInfo {
 	/* Parents for added methods, fields, etc */
 	GHashTable *member_parent; /* maps added methoddef or fielddef tokens to typedef tokens */
 
+	/* Params for added methods */
+	GHashTable *method_params; /* maps methoddef tokens to a MonoClassMetadataUpdateMethodParamInfo* */
+
 	/* Skeletons for all newly-added types from every generation. Accessing the array requires the image lock. */
 	GArray *skeletons;
 };
@@ -412,6 +419,12 @@ baseline_info_destroy (BaselineInfo *info)
 	if (info->skeletons)
  g_array_free (info->skeletons, TRUE);
 
+	if (info->member_parent)
+ g_hash_table_destroy (info->member_parent);
+
+	if (info->method_params)
+ g_hash_table_destroy (info->method_params);
+
 	g_free (info);
 }
 
@@ -627,6 +640,11 @@ add_method_to_baseline (BaselineInfo *base_info, DeltaInfo *delta_info, MonoClas
 static void
 add_field_to_baseline (BaselineInfo *base_info, DeltaInfo *delta_info, MonoClass *klass, uint32_t field_token);
 
+/* Add a method->params lookup for new methods in existing classes */
+static void
+add_param_info_for_method (BaselineInfo *base_info, uint32_t param_token, uint32_t method_token);
+
+
 void
 hot_reload_init (void)
 {
@@ -2019,6 +2037,7 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
 	uint32_t add_member_typedef = 0;
 	uint32_t add_property_propertymap = 0;
 	uint32_t add_event_eventmap = 0;
+	uint32_t add_field_method = 0;
 
 	gboolean assemblyref_updated = FALSE;
 	for (guint32 i = 0; i < rows ; ++i) {
@@ -2049,6 +2068,7 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
 
  case ENC_FUNC_ADD_PARAM: {
  g_assert (token_table == MONO_TABLE_METHOD);
+ add_field_method = log_token;
  break;
  }
  case ENC_FUNC_ADD_FIELD: {
@@ -2115,8 +2135,11 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
  }
  case MONO_TABLE_METHOD: {
  /* if adding a param, handle it with the next record */
- if (func_code == ENC_FUNC_ADD_PARAM)
+ if (func_code == ENC_FUNC_ADD_PARAM) {
+ g_assert (is_addition);
  break;
+ }
+ g_assert (func_code == ENC_FUNC_DEFAULT);
 
  if (!base_info->method_table_update)
  base_info->method_table_update = g_hash_table_new (g_direct_hash, g_direct_equal);
@@ -2366,9 +2389,21 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
  *
  * So by the time we see the param additions, the methods are already in.
  *
- * FIXME: we need a lookaside table (like member_parent) for every place
- * that looks at MONO_METHOD_PARAMLIST
  */
+ if (is_addition) {
+ g_assert (add_field_method != 0);
+ uint32_t parent_type_token = hot_reload_method_parent (image_base, add_field_method);
+ g_assert (parent_type_token != 0); // we added a parameter to a method that was added
+ if (pass2_context_is_skeleton (ctx, parent_type_token)) {
+ // it's a parameter on a new method in a brand new class
+ // FIXME: need to do something here?
+ } else {
+ // it's a parameter on a new method in an existing class
+ add_param_info_for_method (base_info, log_token, add_field_method);
+ }
+ add_field_method = 0;
+ break;
+ }
  break;
  }
  case MONO_TABLE_INTERFACEIMPL: {
@@ -2819,6 +2854,28 @@ hot_reload_field_parent (MonoImage *base_image, uint32_t field_token)
 }
 
 
+static void
+add_param_info_for_method (BaselineInfo *base_info, uint32_t param_token, uint32_t method_token)
+{
+	if (!base_info->method_params) {
+ base_info->method_params = g_hash_table_new_full (g_direct_hash, g_direct_equal, NULL, g_free);
+	}
+	MonoMethodMetadataUpdateParamInfo* info = NULL;
+	info = g_hash_table_lookup (base_info->method_params, GUINT_TO_POINTER (method_token));
+	if (!info) {
+ // FIXME locking
+ info = g_new0 (MonoMethodMetadataUpdateParamInfo, 1);
+ g_hash_table_insert (base_info->method_params, GUINT_TO_POINTER (method_token), info);
+ info->first_param_token = param_token;
+ info->param_count = 1;
+	} else {
+ uint32_t param_index = mono_metadata_token_index (param_token);
+ // expect params for a single method to be a contiguous sequence of rows
+ g_assert (mono_metadata_token_index (info->first_param_token) + info->param_count == param_index);
+ info->param_count++;
+	}
+}
+
 /* HACK - keep in sync with locator_t in metadata/metadata.c */
 typedef struct {
 	guint32 idx; /* The index that we are trying to locate */
@@ -3148,6 +3205,32 @@ hot_reload_get_num_methods_added (MonoClass *klass)
 	return count;
 }
 
+static uint32_t
+hot_reload_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt)
+{
+	BaselineInfo *base_info = baseline_info_lookup (base_image);
+	g_assert (base_info);
+
+	/* FIXME: locking in case the hash table grows */
+
+	if (!base_info->method_params)
+ return 0;
+
+	MonoMethodMetadataUpdateParamInfo* info = NULL;
+	info = g_hash_table_lookup (base_info->method_params, GUINT_TO_POINTER (methoddef_token));
+	if (!info) {
+ if (out_param_count_opt)
+ *out_param_count_opt = 0;
+ return 0;
+	}
+
+	if (out_param_count_opt)
+ *out_param_count_opt = info->param_count;
+
+	return mono_metadata_token_index (info->first_param_token);
+}
+
+
 static const char *
 hot_reload_get_capabilities (void)
 {

src/mono/mono/component/hot_reload.h

@@ -48,6 +48,7 @@ typedef struct _MonoComponentHotReload {
 	uint32_t (*get_num_fields_added) (MonoClass *klass);
 	uint32_t (*get_num_methods_added) (MonoClass *klass);
 	const char* (*get_capabilities) (void);
+	uint32_t (*get_method_params) (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt);
 } MonoComponentHotReload;
 
 MONO_COMPONENT_EXPORT_ENTRYPOINT

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/ReflectionAddNewMethod.cs

@@ -0,0 +1,16 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+using System;
+
+
+namespace System.Reflection.Metadata.ApplyUpdate.Test
+{
+ public class ReflectionAddNewMethod
+ {
+ public string ExistingMethod(string u, double f)
+	{
+ return u + f.ToString();;
+ }
+
+ }
+}

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/ReflectionAddNewMethod_v1.cs

@@ -0,0 +1,21 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+using System;
+using System.Runtime.CompilerServices;
+using CancellationToken = System.Threading.CancellationToken;
+
+namespace System.Reflection.Metadata.ApplyUpdate.Test
+{
+ public class ReflectionAddNewMethod
+ {
+ public string ExistingMethod(string u, double f)
+	{
+ return u + f.ToString();;
+ }
+
+	public double AddedNewMethod(char c, float h, string w, CancellationToken ct = default, [CallerMemberName] string callerName = "")
+	{
+ return ((double)Convert.ToInt32(c)) + h;
+	}
+ }
+}

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod.csproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+ <PropertyGroup>
+ <RootNamespace>System.Runtime.Loader.Tests</RootNamespace>
+ <TargetFramework>$(NetCoreAppCurrent)</TargetFramework>
+ <TestRuntime>true</TestRuntime>
+ <DeltaScript>deltascript.json</DeltaScript>
+ </PropertyGroup>
+ <ItemGroup>
+ <Compile Include="ReflectionAddNewMethod.cs" />
+ </ItemGroup>
+</Project>

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/deltascript.json

@@ -0,0 +1,6 @@
+{
+ "changes": [
+ {"document": "ReflectionAddNewMethod.cs", "update": "ReflectionAddNewMethod_v1.cs"},
+ ]
+}
+

src/libraries/System.Runtime.Loader/tests/ApplyUpdateTest.cs

@@ -3,6 +3,7 @@
 
 using System.Reflection;
 using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
 using Xunit;
 
 namespace System.Reflection.Metadata
@@ -629,5 +630,87 @@ public static void TestReflectionAddNewType()
  System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewType.ZExistingClass.ExistingMethod ();
  });
  }
+
+ [ConditionalFact(typeof(ApplyUpdateUtil), nameof(ApplyUpdateUtil.IsSupported))]
+ public static void TestReflectionAddNewMethod()
+ {
+ ApplyUpdateUtil.TestCase(static () =>
+ {
+ var ty = typeof(System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod);
+ var assm = ty.Assembly;
+
+ var bindingFlags = BindingFlags.Instance | BindingFlags.Public;
+ var allMethods = ty.GetMethods(bindingFlags);
+
+ int objectMethods = typeof(object).GetMethods(bindingFlags).Length;
+ Assert.Equal (objectMethods + 1, allMethods.Length);
+
+ ApplyUpdateUtil.ApplyUpdate(assm);
+ ApplyUpdateUtil.ClearAllReflectionCaches();
+
+ ty = typeof(System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod);
+
+ allMethods = ty.GetMethods(bindingFlags);
+ Assert.Equal (objectMethods + 2, allMethods.Length);
+
+ var mi = ty.GetMethod ("AddedNewMethod");
+
+ Assert.NotNull (mi);
+
+ var retParm = mi.ReturnParameter;
+ Assert.NotNull (retParm);
+ Assert.NotNull (retParm.ParameterType);
+ Assert.Equal (-1, retParm.Position);
+
+ var retCas = retParm.GetCustomAttributes(false);
+ Assert.NotNull(retCas);
+ Assert.Equal(0, retCas.Length);
+
+ var parms = mi.GetParameters();
+ Assert.Equal (5, parms.Length);
+
+ int parmPos = 0;
+ foreach (var parm in parms)
+ {
+ Assert.NotNull(parm);
+ Assert.NotNull(parm.ParameterType);
+ Assert.Equal(parmPos, parm.Position);
+ Assert.NotNull(parm.Name);
+
+ var cas = parm.GetCustomAttributes(false);
+ foreach (var ca in cas) {
+ Assert.NotNull (ca);
+ }
+
+ parmPos++;
+ }
+
+ var parmAttrs = parms[4].GetCustomAttributes(false);
+ Assert.Equal (2, parmAttrs.Length);
+ bool foundCallerMemberName = false;
+ bool foundOptional = false;
+ foreach (var pa in parmAttrs) {
+ if (typeof (CallerMemberNameAttribute).Equals(pa.GetType()))
+ {
+ foundCallerMemberName = true;
+ }
+ if (typeof (OptionalAttribute).Equals(pa.GetType()))
+ {
+ foundOptional = true;
+ }
+ }
+ Assert.True(foundCallerMemberName);
+ Assert.True(foundOptional);
+
+ // n.b. this typeof() also makes the rest of the test work on Wasm with aggressive trimming.
+ Assert.Equal (typeof(System.Threading.CancellationToken), parms[3].ParameterType);
+
+ Assert.True(parms[3].HasDefaultValue);
+ Assert.True(parms[4].HasDefaultValue);
+
+ Assert.Null(parms[3].DefaultValue);
+ Assert.Equal(string.Empty, parms[4].DefaultValue);
+ });
+	} 
  }
 }

src/libraries/System.Runtime.Loader/tests/System.Runtime.Loader.Tests.csproj

@@ -62,6 +62,7 @@
  <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.AddStaticLambda\System.Reflection.Metadata.ApplyUpdate.Test.AddStaticLambda.csproj" />
  <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.StaticLambdaRegression\System.Reflection.Metadata.ApplyUpdate.Test.StaticLambdaRegression.csproj" />
  <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewType\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewType.csproj" />
+ <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod.csproj" />
  </ItemGroup>
  <ItemGroup Condition="'$(TargetOS)' == 'Browser'">
  <WasmFilesToIncludeFromPublishDir Include="$(AssemblyName).dll" />

src/mono/mono/component/hot_reload-internals.h

@@ -86,4 +86,9 @@ typedef struct _MonoClassMetadataUpdateEvent {
 	uint32_t token; /* the Event table token where this event was defined. */
 } MonoClassMetadataUpdateEvent;
 
+typedef struct _MonoMethodMetadataUpdateParamInfo {
+	uint32_t first_param_token; /* a Param token */
+	uint32_t param_count;
+} MonoMethodMetadataUpdateParamInfo;
+
 #endif/*_MONO_COMPONENT_HOT_RELOAD_INTERNALS_H*/

src/mono/mono/component/hot_reload-stub.c

@@ -110,6 +110,9 @@ hot_reload_get_num_methods_added (MonoClass *klass);
 static const char *
 hot_reload_get_capabilities (void);
 
+static uint32_t
+hot_reload_stub_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt);
+
 static MonoComponentHotReload fn_table = {
 	{ MONO_COMPONENT_ITF_VERSION, &hot_reload_stub_available },
 	&hot_reload_stub_set_fastpath_data,
@@ -142,7 +145,8 @@ static MonoComponentHotReload fn_table = {
 	&hot_reload_stub_added_fields_iter,
 	&hot_reload_get_num_fields_added,
 	&hot_reload_get_num_methods_added,
-	&hot_reload_get_capabilities
+	&hot_reload_get_capabilities,
+	&hot_reload_stub_get_method_params,
 };
 
 static bool
@@ -343,6 +347,12 @@ hot_reload_get_capabilities (void)
 	return "";
 }
 
+static uint32_t
+hot_reload_stub_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt)
+{
+	return 0;
+}
+
 MONO_COMPONENT_EXPORT_ENTRYPOINT
 MonoComponentHotReload *
 mono_component_hot_reload_init (void)

src/mono/mono/component/hot_reload.c

@@ -144,6 +144,9 @@ hot_reload_get_num_methods_added (MonoClass *klass);
 static const char *
 hot_reload_get_capabilities (void);
 
+static uint32_t
+hot_reload_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt);
+
 static MonoClassMetadataUpdateField *
 metadata_update_field_setup_basic_info (MonoImage *image_base, BaselineInfo *base_info, uint32_t generation, DeltaInfo *delta_info, MonoClass *parent_klass, uint32_t fielddef_token, uint32_t field_flags);
 
@@ -179,7 +182,8 @@ static MonoComponentHotReload fn_table = {
 	&hot_reload_added_fields_iter,
 	&hot_reload_get_num_fields_added,
 	&hot_reload_get_num_methods_added,
-	&hot_reload_get_capabilities
+	&hot_reload_get_capabilities,
+	&hot_reload_get_method_params,
 };
 
 MonoComponentHotReload *
@@ -272,6 +276,9 @@ struct _BaselineInfo {
 	/* Parents for added methods, fields, etc */
 	GHashTable *member_parent; /* maps added methoddef or fielddef tokens to typedef tokens */
 
+	/* Params for added methods */
+	GHashTable *method_params; /* maps methoddef tokens to a MonoClassMetadataUpdateMethodParamInfo* */
+
 	/* Skeletons for all newly-added types from every generation. Accessing the array requires the image lock. */
 	GArray *skeletons;
 };
@@ -412,6 +419,12 @@ baseline_info_destroy (BaselineInfo *info)
 	if (info->skeletons)
  g_array_free (info->skeletons, TRUE);
 
+	if (info->member_parent)
+ g_hash_table_destroy (info->member_parent);
+
+	if (info->method_params)
+ g_hash_table_destroy (info->method_params);
+
 	g_free (info);
 }
 
@@ -627,6 +640,11 @@ add_method_to_baseline (BaselineInfo *base_info, DeltaInfo *delta_info, MonoClas
 static void
 add_field_to_baseline (BaselineInfo *base_info, DeltaInfo *delta_info, MonoClass *klass, uint32_t field_token);
 
+/* Add a method->params lookup for new methods in existing classes */
+static void
+add_param_info_for_method (BaselineInfo *base_info, uint32_t param_token, uint32_t method_token);
+
+
 void
 hot_reload_init (void)
 {
@@ -2019,6 +2037,7 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
 	uint32_t add_member_typedef = 0;
 	uint32_t add_property_propertymap = 0;
 	uint32_t add_event_eventmap = 0;
+	uint32_t add_field_method = 0;
 
 	gboolean assemblyref_updated = FALSE;
 	for (guint32 i = 0; i < rows ; ++i) {
@@ -2049,6 +2068,7 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
 
  case ENC_FUNC_ADD_PARAM: {
  g_assert (token_table == MONO_TABLE_METHOD);
+ add_field_method = log_token;
  break;
  }
  case ENC_FUNC_ADD_FIELD: {
@@ -2115,8 +2135,11 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
  }
  case MONO_TABLE_METHOD: {
  /* if adding a param, handle it with the next record */
- if (func_code == ENC_FUNC_ADD_PARAM)
+ if (func_code == ENC_FUNC_ADD_PARAM) {
+ g_assert (is_addition);
  break;
+ }
+ g_assert (func_code == ENC_FUNC_DEFAULT);
 
  if (!base_info->method_table_update)
  base_info->method_table_update = g_hash_table_new (g_direct_hash, g_direct_equal);
@@ -2366,9 +2389,21 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
  *
  * So by the time we see the param additions, the methods are already in.
  *
- * FIXME: we need a lookaside table (like member_parent) for every place
- * that looks at MONO_METHOD_PARAMLIST
  */
+ if (is_addition) {
+ g_assert (add_field_method != 0);
+ uint32_t parent_type_token = hot_reload_method_parent (image_base, add_field_method);
+ g_assert (parent_type_token != 0); // we added a parameter to a method that was added
+ if (pass2_context_is_skeleton (ctx, parent_type_token)) {
+ // it's a parameter on a new method in a brand new class
+ // FIXME: need to do something here?
+ } else {
+ // it's a parameter on a new method in an existing class
+ add_param_info_for_method (base_info, log_token, add_field_method);
+ }
+ add_field_method = 0;
+ break;
+ }
  break;
  }
  case MONO_TABLE_INTERFACEIMPL: {
@@ -2819,6 +2854,28 @@ hot_reload_field_parent (MonoImage *base_image, uint32_t field_token)
 }
 
 
+static void
+add_param_info_for_method (BaselineInfo *base_info, uint32_t param_token, uint32_t method_token)
+{
+	if (!base_info->method_params) {
+ base_info->method_params = g_hash_table_new_full (g_direct_hash, g_direct_equal, NULL, g_free);
+	}
+	MonoMethodMetadataUpdateParamInfo* info = NULL;
+	info = g_hash_table_lookup (base_info->method_params, GUINT_TO_POINTER (method_token));
+	if (!info) {
+ // FIXME locking
+ info = g_new0 (MonoMethodMetadataUpdateParamInfo, 1);
+ g_hash_table_insert (base_info->method_params, GUINT_TO_POINTER (method_token), info);
+ info->first_param_token = param_token;
+ info->param_count = 1;
+	} else {
+ uint32_t param_index = mono_metadata_token_index (param_token);
+ // expect params for a single method to be a contiguous sequence of rows
+ g_assert (mono_metadata_token_index (info->first_param_token) + info->param_count == param_index);
+ info->param_count++;
+	}
+}
+
 /* HACK - keep in sync with locator_t in metadata/metadata.c */
 typedef struct {
 	guint32 idx; /* The index that we are trying to locate */
@@ -3148,6 +3205,32 @@ hot_reload_get_num_methods_added (MonoClass *klass)
 	return count;
 }
 
+static uint32_t
+hot_reload_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt)
+{
+	BaselineInfo *base_info = baseline_info_lookup (base_image);
+	g_assert (base_info);
+
+	/* FIXME: locking in case the hash table grows */
+
+	if (!base_info->method_params)
+ return 0;
+
+	MonoMethodMetadataUpdateParamInfo* info = NULL;
+	info = g_hash_table_lookup (base_info->method_params, GUINT_TO_POINTER (methoddef_token));
+	if (!info) {
+ if (out_param_count_opt)
+ *out_param_count_opt = 0;
+ return 0;
+	}
+
+	if (out_param_count_opt)
+ *out_param_count_opt = info->param_count;
+
+	return mono_metadata_token_index (info->first_param_token);
+}
+
+
 static const char *
 hot_reload_get_capabilities (void)
 {

src/mono/mono/component/hot_reload.h

@@ -48,6 +48,7 @@ typedef struct _MonoComponentHotReload {
 	uint32_t (*get_num_fields_added) (MonoClass *klass);
 	uint32_t (*get_num_methods_added) (MonoClass *klass);
 	const char* (*get_capabilities) (void);
+	uint32_t (*get_method_params) (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt);
 } MonoComponentHotReload;
 
 MONO_COMPONENT_EXPORT_ENTRYPOINT

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/ReflectionAddNewMethod.cs

@@ -0,0 +1,16 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+using System;
+
+
+namespace System.Reflection.Metadata.ApplyUpdate.Test
+{
+ public class ReflectionAddNewMethod
+ {
+ public string ExistingMethod(string u, double f)
+	{
+ return u + f.ToString();;
+ }
+
+ }
+}

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/ReflectionAddNewMethod_v1.cs

@@ -0,0 +1,21 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+using System;
+using System.Runtime.CompilerServices;
+using CancellationToken = System.Threading.CancellationToken;
+
+namespace System.Reflection.Metadata.ApplyUpdate.Test
+{
+ public class ReflectionAddNewMethod
+ {
+ public string ExistingMethod(string u, double f)
+	{
+ return u + f.ToString();;
+ }
+
+	public double AddedNewMethod(char c, float h, string w, CancellationToken ct = default, [CallerMemberName] string callerName = "")
+	{
+ return ((double)Convert.ToInt32(c)) + h;
+	}
+ }
+}

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod.csproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+ <PropertyGroup>
+ <RootNamespace>System.Runtime.Loader.Tests</RootNamespace>
+ <TargetFramework>$(NetCoreAppCurrent)</TargetFramework>
+ <TestRuntime>true</TestRuntime>
+ <DeltaScript>deltascript.json</DeltaScript>
+ </PropertyGroup>
+ <ItemGroup>
+ <Compile Include="ReflectionAddNewMethod.cs" />
+ </ItemGroup>
+</Project>

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/deltascript.json

@@ -0,0 +1,6 @@
+{
+ "changes": [
+ {"document": "ReflectionAddNewMethod.cs", "update": "ReflectionAddNewMethod_v1.cs"},
+ ]
+}
+

src/libraries/System.Runtime.Loader/tests/ApplyUpdateTest.cs

@@ -3,6 +3,7 @@
 
 using System.Reflection;
 using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
 using Xunit;
 
 namespace System.Reflection.Metadata
@@ -629,5 +630,87 @@ public static void TestReflectionAddNewType()
  System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewType.ZExistingClass.ExistingMethod ();
  });
  }
+
+ [ConditionalFact(typeof(ApplyUpdateUtil), nameof(ApplyUpdateUtil.IsSupported))]
+ public static void TestReflectionAddNewMethod()
+ {
+ ApplyUpdateUtil.TestCase(static () =>
+ {
+ var ty = typeof(System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod);
+ var assm = ty.Assembly;
+
+ var bindingFlags = BindingFlags.Instance | BindingFlags.Public;
+ var allMethods = ty.GetMethods(bindingFlags);
+
+ int objectMethods = typeof(object).GetMethods(bindingFlags).Length;
+ Assert.Equal (objectMethods + 1, allMethods.Length);
+
+ ApplyUpdateUtil.ApplyUpdate(assm);
+ ApplyUpdateUtil.ClearAllReflectionCaches();
+
+ ty = typeof(System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod);
+
+ allMethods = ty.GetMethods(bindingFlags);
+ Assert.Equal (objectMethods + 2, allMethods.Length);
+
+ var mi = ty.GetMethod ("AddedNewMethod");
+
+ Assert.NotNull (mi);
+
+ var retParm = mi.ReturnParameter;
+ Assert.NotNull (retParm);
+ Assert.NotNull (retParm.ParameterType);
+ Assert.Equal (-1, retParm.Position);
+
+ var retCas = retParm.GetCustomAttributes(false);
+ Assert.NotNull(retCas);
+ Assert.Equal(0, retCas.Length);
+
+ var parms = mi.GetParameters();
+ Assert.Equal (5, parms.Length);
+
+ int parmPos = 0;
+ foreach (var parm in parms)
+ {
+ Assert.NotNull(parm);
+ Assert.NotNull(parm.ParameterType);
+ Assert.Equal(parmPos, parm.Position);
+ Assert.NotNull(parm.Name);
+
+ var cas = parm.GetCustomAttributes(false);
+ foreach (var ca in cas) {
+ Assert.NotNull (ca);
+ }
+
+ parmPos++;
+ }
+
+ var parmAttrs = parms[4].GetCustomAttributes(false);
+ Assert.Equal (2, parmAttrs.Length);
+ bool foundCallerMemberName = false;
+ bool foundOptional = false;
+ foreach (var pa in parmAttrs) {
+ if (typeof (CallerMemberNameAttribute).Equals(pa.GetType()))
+ {
+ foundCallerMemberName = true;
+ }
+ if (typeof (OptionalAttribute).Equals(pa.GetType()))
+ {
+ foundOptional = true;
+ }
+ }
+ Assert.True(foundCallerMemberName);
+ Assert.True(foundOptional);
+
+ // n.b. this typeof() also makes the rest of the test work on Wasm with aggressive trimming.
+ Assert.Equal (typeof(System.Threading.CancellationToken), parms[3].ParameterType);
+
+ Assert.True(parms[3].HasDefaultValue);
+ Assert.True(parms[4].HasDefaultValue);
+
+ Assert.Null(parms[3].DefaultValue);
+ Assert.Equal(string.Empty, parms[4].DefaultValue);
+ });
+	} 
  }
 }

src/libraries/System.Runtime.Loader/tests/System.Runtime.Loader.Tests.csproj

@@ -62,6 +62,7 @@
  <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.AddStaticLambda\System.Reflection.Metadata.ApplyUpdate.Test.AddStaticLambda.csproj" />
  <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.StaticLambdaRegression\System.Reflection.Metadata.ApplyUpdate.Test.StaticLambdaRegression.csproj" />
  <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewType\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewType.csproj" />
+ <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod.csproj" />
  </ItemGroup>
  <ItemGroup Condition="'$(TargetOS)' == 'Browser'">
  <WasmFilesToIncludeFromPublishDir Include="$(AssemblyName).dll" />

src/mono/mono/component/hot_reload-internals.h

@@ -86,4 +86,9 @@ typedef struct _MonoClassMetadataUpdateEvent {
 	uint32_t token; /* the Event table token where this event was defined. */
 } MonoClassMetadataUpdateEvent;
 
+typedef struct _MonoMethodMetadataUpdateParamInfo {
+	uint32_t first_param_token; /* a Param token */
+	uint32_t param_count;
+} MonoMethodMetadataUpdateParamInfo;
+
 #endif/*_MONO_COMPONENT_HOT_RELOAD_INTERNALS_H*/

src/mono/mono/component/hot_reload-stub.c

@@ -110,6 +110,9 @@ hot_reload_get_num_methods_added (MonoClass *klass);
 static const char *
 hot_reload_get_capabilities (void);
 
+static uint32_t
+hot_reload_stub_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt);
+
 static MonoComponentHotReload fn_table = {
 	{ MONO_COMPONENT_ITF_VERSION, &hot_reload_stub_available },
 	&hot_reload_stub_set_fastpath_data,
@@ -142,7 +145,8 @@ static MonoComponentHotReload fn_table = {
 	&hot_reload_stub_added_fields_iter,
 	&hot_reload_get_num_fields_added,
 	&hot_reload_get_num_methods_added,
-	&hot_reload_get_capabilities
+	&hot_reload_get_capabilities,
+	&hot_reload_stub_get_method_params,
 };
 
 static bool
@@ -343,6 +347,12 @@ hot_reload_get_capabilities (void)
 	return "";
 }
 
+static uint32_t
+hot_reload_stub_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt)
+{
+	return 0;
+}
+
 MONO_COMPONENT_EXPORT_ENTRYPOINT
 MonoComponentHotReload *
 mono_component_hot_reload_init (void)

src/mono/mono/component/hot_reload.c

@@ -144,6 +144,9 @@ hot_reload_get_num_methods_added (MonoClass *klass);
 static const char *
 hot_reload_get_capabilities (void);
 
+static uint32_t
+hot_reload_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt);
+
 static MonoClassMetadataUpdateField *
 metadata_update_field_setup_basic_info (MonoImage *image_base, BaselineInfo *base_info, uint32_t generation, DeltaInfo *delta_info, MonoClass *parent_klass, uint32_t fielddef_token, uint32_t field_flags);
 
@@ -179,7 +182,8 @@ static MonoComponentHotReload fn_table = {
 	&hot_reload_added_fields_iter,
 	&hot_reload_get_num_fields_added,
 	&hot_reload_get_num_methods_added,
-	&hot_reload_get_capabilities
+	&hot_reload_get_capabilities,
+	&hot_reload_get_method_params,
 };
 
 MonoComponentHotReload *
@@ -272,6 +276,9 @@ struct _BaselineInfo {
 	/* Parents for added methods, fields, etc */
 	GHashTable *member_parent; /* maps added methoddef or fielddef tokens to typedef tokens */
 
+	/* Params for added methods */
+	GHashTable *method_params; /* maps methoddef tokens to a MonoClassMetadataUpdateMethodParamInfo* */
+
 	/* Skeletons for all newly-added types from every generation. Accessing the array requires the image lock. */
 	GArray *skeletons;
 };
@@ -412,6 +419,12 @@ baseline_info_destroy (BaselineInfo *info)
 	if (info->skeletons)
  g_array_free (info->skeletons, TRUE);
 
+	if (info->member_parent)
+ g_hash_table_destroy (info->member_parent);
+
+	if (info->method_params)
+ g_hash_table_destroy (info->method_params);
+
 	g_free (info);
 }
 
@@ -627,6 +640,11 @@ add_method_to_baseline (BaselineInfo *base_info, DeltaInfo *delta_info, MonoClas
 static void
 add_field_to_baseline (BaselineInfo *base_info, DeltaInfo *delta_info, MonoClass *klass, uint32_t field_token);
 
+/* Add a method->params lookup for new methods in existing classes */
+static void
+add_param_info_for_method (BaselineInfo *base_info, uint32_t param_token, uint32_t method_token);
+
+
 void
 hot_reload_init (void)
 {
@@ -2019,6 +2037,7 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
 	uint32_t add_member_typedef = 0;
 	uint32_t add_property_propertymap = 0;
 	uint32_t add_event_eventmap = 0;
+	uint32_t add_field_method = 0;
 
 	gboolean assemblyref_updated = FALSE;
 	for (guint32 i = 0; i < rows ; ++i) {
@@ -2049,6 +2068,7 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
 
  case ENC_FUNC_ADD_PARAM: {
  g_assert (token_table == MONO_TABLE_METHOD);
+ add_field_method = log_token;
  break;
  }
  case ENC_FUNC_ADD_FIELD: {
@@ -2115,8 +2135,11 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
  }
  case MONO_TABLE_METHOD: {
  /* if adding a param, handle it with the next record */
- if (func_code == ENC_FUNC_ADD_PARAM)
+ if (func_code == ENC_FUNC_ADD_PARAM) {
+ g_assert (is_addition);
  break;
+ }
+ g_assert (func_code == ENC_FUNC_DEFAULT);
 
  if (!base_info->method_table_update)
  base_info->method_table_update = g_hash_table_new (g_direct_hash, g_direct_equal);
@@ -2366,9 +2389,21 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
  *
  * So by the time we see the param additions, the methods are already in.
  *
- * FIXME: we need a lookaside table (like member_parent) for every place
- * that looks at MONO_METHOD_PARAMLIST
  */
+ if (is_addition) {
+ g_assert (add_field_method != 0);
+ uint32_t parent_type_token = hot_reload_method_parent (image_base, add_field_method);
+ g_assert (parent_type_token != 0); // we added a parameter to a method that was added
+ if (pass2_context_is_skeleton (ctx, parent_type_token)) {
+ // it's a parameter on a new method in a brand new class
+ // FIXME: need to do something here?
+ } else {
+ // it's a parameter on a new method in an existing class
+ add_param_info_for_method (base_info, log_token, add_field_method);
+ }
+ add_field_method = 0;
+ break;
+ }
  break;
  }
  case MONO_TABLE_INTERFACEIMPL: {
@@ -2819,6 +2854,28 @@ hot_reload_field_parent (MonoImage *base_image, uint32_t field_token)
 }
 
 
+static void
+add_param_info_for_method (BaselineInfo *base_info, uint32_t param_token, uint32_t method_token)
+{
+	if (!base_info->method_params) {
+ base_info->method_params = g_hash_table_new_full (g_direct_hash, g_direct_equal, NULL, g_free);
+	}
+	MonoMethodMetadataUpdateParamInfo* info = NULL;
+	info = g_hash_table_lookup (base_info->method_params, GUINT_TO_POINTER (method_token));
+	if (!info) {
+ // FIXME locking
+ info = g_new0 (MonoMethodMetadataUpdateParamInfo, 1);
+ g_hash_table_insert (base_info->method_params, GUINT_TO_POINTER (method_token), info);
+ info->first_param_token = param_token;
+ info->param_count = 1;
+	} else {
+ uint32_t param_index = mono_metadata_token_index (param_token);
+ // expect params for a single method to be a contiguous sequence of rows
+ g_assert (mono_metadata_token_index (info->first_param_token) + info->param_count == param_index);
+ info->param_count++;
+	}
+}
+
 /* HACK - keep in sync with locator_t in metadata/metadata.c */
 typedef struct {
 	guint32 idx; /* The index that we are trying to locate */
@@ -3148,6 +3205,32 @@ hot_reload_get_num_methods_added (MonoClass *klass)
 	return count;
 }
 
+static uint32_t
+hot_reload_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt)
+{
+	BaselineInfo *base_info = baseline_info_lookup (base_image);
+	g_assert (base_info);
+
+	/* FIXME: locking in case the hash table grows */
+
+	if (!base_info->method_params)
+ return 0;
+
+	MonoMethodMetadataUpdateParamInfo* info = NULL;
+	info = g_hash_table_lookup (base_info->method_params, GUINT_TO_POINTER (methoddef_token));
+	if (!info) {
+ if (out_param_count_opt)
+ *out_param_count_opt = 0;
+ return 0;
+	}
+
+	if (out_param_count_opt)
+ *out_param_count_opt = info->param_count;
+
+	return mono_metadata_token_index (info->first_param_token);
+}
+
+
 static const char *
 hot_reload_get_capabilities (void)
 {

src/mono/mono/component/hot_reload.h

@@ -48,6 +48,7 @@ typedef struct _MonoComponentHotReload {
 	uint32_t (*get_num_fields_added) (MonoClass *klass);
 	uint32_t (*get_num_methods_added) (MonoClass *klass);
 	const char* (*get_capabilities) (void);
+	uint32_t (*get_method_params) (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt);
 } MonoComponentHotReload;
 
 MONO_COMPONENT_EXPORT_ENTRYPOINT

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/ReflectionAddNewMethod.cs

@@ -0,0 +1,16 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+using System;
+
+
+namespace System.Reflection.Metadata.ApplyUpdate.Test
+{
+ public class ReflectionAddNewMethod
+ {
+ public string ExistingMethod(string u, double f)
+	{
+ return u + f.ToString();;
+ }
+
+ }
+}

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/ReflectionAddNewMethod_v1.cs

@@ -0,0 +1,21 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+using System;
+using System.Runtime.CompilerServices;
+using CancellationToken = System.Threading.CancellationToken;
+
+namespace System.Reflection.Metadata.ApplyUpdate.Test
+{
+ public class ReflectionAddNewMethod
+ {
+ public string ExistingMethod(string u, double f)
+	{
+ return u + f.ToString();;
+ }
+
+	public double AddedNewMethod(char c, float h, string w, CancellationToken ct = default, [CallerMemberName] string callerName = "")
+	{
+ return ((double)Convert.ToInt32(c)) + h;
+	}
+ }
+}

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod.csproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+ <PropertyGroup>
+ <RootNamespace>System.Runtime.Loader.Tests</RootNamespace>
+ <TargetFramework>$(NetCoreAppCurrent)</TargetFramework>
+ <TestRuntime>true</TestRuntime>
+ <DeltaScript>deltascript.json</DeltaScript>
+ </PropertyGroup>
+ <ItemGroup>
+ <Compile Include="ReflectionAddNewMethod.cs" />
+ </ItemGroup>
+</Project>

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/deltascript.json

@@ -0,0 +1,6 @@
+{
+ "changes": [
+ {"document": "ReflectionAddNewMethod.cs", "update": "ReflectionAddNewMethod_v1.cs"},
+ ]
+}
+

src/libraries/System.Runtime.Loader/tests/ApplyUpdateTest.cs

@@ -3,6 +3,7 @@
 
 using System.Reflection;
 using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
 using Xunit;
 
 namespace System.Reflection.Metadata
@@ -629,5 +630,87 @@ public static void TestReflectionAddNewType()
  System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewType.ZExistingClass.ExistingMethod ();
  });
  }
+
+ [ConditionalFact(typeof(ApplyUpdateUtil), nameof(ApplyUpdateUtil.IsSupported))]
+ public static void TestReflectionAddNewMethod()
+ {
+ ApplyUpdateUtil.TestCase(static () =>
+ {
+ var ty = typeof(System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod);
+ var assm = ty.Assembly;
+
+ var bindingFlags = BindingFlags.Instance | BindingFlags.Public;
+ var allMethods = ty.GetMethods(bindingFlags);
+
+ int objectMethods = typeof(object).GetMethods(bindingFlags).Length;
+ Assert.Equal (objectMethods + 1, allMethods.Length);
+
+ ApplyUpdateUtil.ApplyUpdate(assm);
+ ApplyUpdateUtil.ClearAllReflectionCaches();
+
+ ty = typeof(System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod);
+
+ allMethods = ty.GetMethods(bindingFlags);
+ Assert.Equal (objectMethods + 2, allMethods.Length);
+
+ var mi = ty.GetMethod ("AddedNewMethod");
+
+ Assert.NotNull (mi);
+
+ var retParm = mi.ReturnParameter;
+ Assert.NotNull (retParm);
+ Assert.NotNull (retParm.ParameterType);
+ Assert.Equal (-1, retParm.Position);
+
+ var retCas = retParm.GetCustomAttributes(false);
+ Assert.NotNull(retCas);
+ Assert.Equal(0, retCas.Length);
+
+ var parms = mi.GetParameters();
+ Assert.Equal (5, parms.Length);
+
+ int parmPos = 0;
+ foreach (var parm in parms)
+ {
+ Assert.NotNull(parm);
+ Assert.NotNull(parm.ParameterType);
+ Assert.Equal(parmPos, parm.Position);
+ Assert.NotNull(parm.Name);
+
+ var cas = parm.GetCustomAttributes(false);
+ foreach (var ca in cas) {
+ Assert.NotNull (ca);
+ }
+
+ parmPos++;
+ }
+
+ var parmAttrs = parms[4].GetCustomAttributes(false);
+ Assert.Equal (2, parmAttrs.Length);
+ bool foundCallerMemberName = false;
+ bool foundOptional = false;
+ foreach (var pa in parmAttrs) {
+ if (typeof (CallerMemberNameAttribute).Equals(pa.GetType()))
+ {
+ foundCallerMemberName = true;
+ }
+ if (typeof (OptionalAttribute).Equals(pa.GetType()))
+ {
+ foundOptional = true;
+ }
+ }
+ Assert.True(foundCallerMemberName);
+ Assert.True(foundOptional);
+
+ // n.b. this typeof() also makes the rest of the test work on Wasm with aggressive trimming.
+ Assert.Equal (typeof(System.Threading.CancellationToken), parms[3].ParameterType);
+
+ Assert.True(parms[3].HasDefaultValue);
+ Assert.True(parms[4].HasDefaultValue);
+
+ Assert.Null(parms[3].DefaultValue);
+ Assert.Equal(string.Empty, parms[4].DefaultValue);
+ });
+	} 
  }
 }

src/libraries/System.Runtime.Loader/tests/System.Runtime.Loader.Tests.csproj

@@ -62,6 +62,7 @@
  <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.AddStaticLambda\System.Reflection.Metadata.ApplyUpdate.Test.AddStaticLambda.csproj" />
  <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.StaticLambdaRegression\System.Reflection.Metadata.ApplyUpdate.Test.StaticLambdaRegression.csproj" />
  <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewType\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewType.csproj" />
+ <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod.csproj" />
  </ItemGroup>
  <ItemGroup Condition="'$(TargetOS)' == 'Browser'">
  <WasmFilesToIncludeFromPublishDir Include="$(AssemblyName).dll" />

src/mono/mono/component/hot_reload-internals.h

@@ -86,4 +86,9 @@ typedef struct _MonoClassMetadataUpdateEvent {
 	uint32_t token; /* the Event table token where this event was defined. */
 } MonoClassMetadataUpdateEvent;
 
+typedef struct _MonoMethodMetadataUpdateParamInfo {
+	uint32_t first_param_token; /* a Param token */
+	uint32_t param_count;
+} MonoMethodMetadataUpdateParamInfo;
+
 #endif/*_MONO_COMPONENT_HOT_RELOAD_INTERNALS_H*/

src/mono/mono/component/hot_reload-stub.c

@@ -110,6 +110,9 @@ hot_reload_get_num_methods_added (MonoClass *klass);
 static const char *
 hot_reload_get_capabilities (void);
 
+static uint32_t
+hot_reload_stub_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt);
+
 static MonoComponentHotReload fn_table = {
 	{ MONO_COMPONENT_ITF_VERSION, &hot_reload_stub_available },
 	&hot_reload_stub_set_fastpath_data,
@@ -142,7 +145,8 @@ static MonoComponentHotReload fn_table = {
 	&hot_reload_stub_added_fields_iter,
 	&hot_reload_get_num_fields_added,
 	&hot_reload_get_num_methods_added,
-	&hot_reload_get_capabilities
+	&hot_reload_get_capabilities,
+	&hot_reload_stub_get_method_params,
 };
 
 static bool
@@ -343,6 +347,12 @@ hot_reload_get_capabilities (void)
 	return "";
 }
 
+static uint32_t
+hot_reload_stub_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt)
+{
+	return 0;
+}
+
 MONO_COMPONENT_EXPORT_ENTRYPOINT
 MonoComponentHotReload *
 mono_component_hot_reload_init (void)

src/mono/mono/component/hot_reload.c

@@ -144,6 +144,9 @@ hot_reload_get_num_methods_added (MonoClass *klass);
 static const char *
 hot_reload_get_capabilities (void);
 
+static uint32_t
+hot_reload_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt);
+
 static MonoClassMetadataUpdateField *
 metadata_update_field_setup_basic_info (MonoImage *image_base, BaselineInfo *base_info, uint32_t generation, DeltaInfo *delta_info, MonoClass *parent_klass, uint32_t fielddef_token, uint32_t field_flags);
 
@@ -179,7 +182,8 @@ static MonoComponentHotReload fn_table = {
 	&hot_reload_added_fields_iter,
 	&hot_reload_get_num_fields_added,
 	&hot_reload_get_num_methods_added,
-	&hot_reload_get_capabilities
+	&hot_reload_get_capabilities,
+	&hot_reload_get_method_params,
 };
 
 MonoComponentHotReload *
@@ -272,6 +276,9 @@ struct _BaselineInfo {
 	/* Parents for added methods, fields, etc */
 	GHashTable *member_parent; /* maps added methoddef or fielddef tokens to typedef tokens */
 
+	/* Params for added methods */
+	GHashTable *method_params; /* maps methoddef tokens to a MonoClassMetadataUpdateMethodParamInfo* */
+
 	/* Skeletons for all newly-added types from every generation. Accessing the array requires the image lock. */
 	GArray *skeletons;
 };
@@ -412,6 +419,12 @@ baseline_info_destroy (BaselineInfo *info)
 	if (info->skeletons)
  g_array_free (info->skeletons, TRUE);
 
+	if (info->member_parent)
+ g_hash_table_destroy (info->member_parent);
+
+	if (info->method_params)
+ g_hash_table_destroy (info->method_params);
+
 	g_free (info);
 }
 
@@ -627,6 +640,11 @@ add_method_to_baseline (BaselineInfo *base_info, DeltaInfo *delta_info, MonoClas
 static void
 add_field_to_baseline (BaselineInfo *base_info, DeltaInfo *delta_info, MonoClass *klass, uint32_t field_token);
 
+/* Add a method->params lookup for new methods in existing classes */
+static void
+add_param_info_for_method (BaselineInfo *base_info, uint32_t param_token, uint32_t method_token);
+
+
 void
 hot_reload_init (void)
 {
@@ -2019,6 +2037,7 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
 	uint32_t add_member_typedef = 0;
 	uint32_t add_property_propertymap = 0;
 	uint32_t add_event_eventmap = 0;
+	uint32_t add_field_method = 0;
 
 	gboolean assemblyref_updated = FALSE;
 	for (guint32 i = 0; i < rows ; ++i) {
@@ -2049,6 +2068,7 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
 
  case ENC_FUNC_ADD_PARAM: {
  g_assert (token_table == MONO_TABLE_METHOD);
+ add_field_method = log_token;
  break;
  }
  case ENC_FUNC_ADD_FIELD: {
@@ -2115,8 +2135,11 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
  }
  case MONO_TABLE_METHOD: {
  /* if adding a param, handle it with the next record */
- if (func_code == ENC_FUNC_ADD_PARAM)
+ if (func_code == ENC_FUNC_ADD_PARAM) {
+ g_assert (is_addition);
  break;
+ }
+ g_assert (func_code == ENC_FUNC_DEFAULT);
 
  if (!base_info->method_table_update)
  base_info->method_table_update = g_hash_table_new (g_direct_hash, g_direct_equal);
@@ -2366,9 +2389,21 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
  *
  * So by the time we see the param additions, the methods are already in.
  *
- * FIXME: we need a lookaside table (like member_parent) for every place
- * that looks at MONO_METHOD_PARAMLIST
  */
+ if (is_addition) {
+ g_assert (add_field_method != 0);
+ uint32_t parent_type_token = hot_reload_method_parent (image_base, add_field_method);
+ g_assert (parent_type_token != 0); // we added a parameter to a method that was added
+ if (pass2_context_is_skeleton (ctx, parent_type_token)) {
+ // it's a parameter on a new method in a brand new class
+ // FIXME: need to do something here?
+ } else {
+ // it's a parameter on a new method in an existing class
+ add_param_info_for_method (base_info, log_token, add_field_method);
+ }
+ add_field_method = 0;
+ break;
+ }
  break;
  }
  case MONO_TABLE_INTERFACEIMPL: {
@@ -2819,6 +2854,28 @@ hot_reload_field_parent (MonoImage *base_image, uint32_t field_token)
 }
 
 
+static void
+add_param_info_for_method (BaselineInfo *base_info, uint32_t param_token, uint32_t method_token)
+{
+	if (!base_info->method_params) {
+ base_info->method_params = g_hash_table_new_full (g_direct_hash, g_direct_equal, NULL, g_free);
+	}
+	MonoMethodMetadataUpdateParamInfo* info = NULL;
+	info = g_hash_table_lookup (base_info->method_params, GUINT_TO_POINTER (method_token));
+	if (!info) {
+ // FIXME locking
+ info = g_new0 (MonoMethodMetadataUpdateParamInfo, 1);
+ g_hash_table_insert (base_info->method_params, GUINT_TO_POINTER (method_token), info);
+ info->first_param_token = param_token;
+ info->param_count = 1;
+	} else {
+ uint32_t param_index = mono_metadata_token_index (param_token);
+ // expect params for a single method to be a contiguous sequence of rows
+ g_assert (mono_metadata_token_index (info->first_param_token) + info->param_count == param_index);
+ info->param_count++;
+	}
+}
+
 /* HACK - keep in sync with locator_t in metadata/metadata.c */
 typedef struct {
 	guint32 idx; /* The index that we are trying to locate */
@@ -3148,6 +3205,32 @@ hot_reload_get_num_methods_added (MonoClass *klass)
 	return count;
 }
 
+static uint32_t
+hot_reload_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt)
+{
+	BaselineInfo *base_info = baseline_info_lookup (base_image);
+	g_assert (base_info);
+
+	/* FIXME: locking in case the hash table grows */
+
+	if (!base_info->method_params)
+ return 0;
+
+	MonoMethodMetadataUpdateParamInfo* info = NULL;
+	info = g_hash_table_lookup (base_info->method_params, GUINT_TO_POINTER (methoddef_token));
+	if (!info) {
+ if (out_param_count_opt)
+ *out_param_count_opt = 0;
+ return 0;
+	}
+
+	if (out_param_count_opt)
+ *out_param_count_opt = info->param_count;
+
+	return mono_metadata_token_index (info->first_param_token);
+}
+
+
 static const char *
 hot_reload_get_capabilities (void)
 {

src/mono/mono/component/hot_reload.h

@@ -48,6 +48,7 @@ typedef struct _MonoComponentHotReload {
 	uint32_t (*get_num_fields_added) (MonoClass *klass);
 	uint32_t (*get_num_methods_added) (MonoClass *klass);
 	const char* (*get_capabilities) (void);
+	uint32_t (*get_method_params) (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt);
 } MonoComponentHotReload;
 
 MONO_COMPONENT_EXPORT_ENTRYPOINT

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/ReflectionAddNewMethod.cs

@@ -0,0 +1,16 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+using System;
+
+
+namespace System.Reflection.Metadata.ApplyUpdate.Test
+{
+ public class ReflectionAddNewMethod
+ {
+ public string ExistingMethod(string u, double f)
+	{
+ return u + f.ToString();;
+ }
+
+ }
+}

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/ReflectionAddNewMethod_v1.cs

@@ -0,0 +1,21 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+using System;
+using System.Runtime.CompilerServices;
+using CancellationToken = System.Threading.CancellationToken;
+
+namespace System.Reflection.Metadata.ApplyUpdate.Test
+{
+ public class ReflectionAddNewMethod
+ {
+ public string ExistingMethod(string u, double f)
+	{
+ return u + f.ToString();;
+ }
+
+	public double AddedNewMethod(char c, float h, string w, CancellationToken ct = default, [CallerMemberName] string callerName = "")
+	{
+ return ((double)Convert.ToInt32(c)) + h;
+	}
+ }
+}

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod.csproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+ <PropertyGroup>
+ <RootNamespace>System.Runtime.Loader.Tests</RootNamespace>
+ <TargetFramework>$(NetCoreAppCurrent)</TargetFramework>
+ <TestRuntime>true</TestRuntime>
+ <DeltaScript>deltascript.json</DeltaScript>
+ </PropertyGroup>
+ <ItemGroup>
+ <Compile Include="ReflectionAddNewMethod.cs" />
+ </ItemGroup>
+</Project>

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/deltascript.json

@@ -0,0 +1,6 @@
+{
+ "changes": [
+ {"document": "ReflectionAddNewMethod.cs", "update": "ReflectionAddNewMethod_v1.cs"},
+ ]
+}
+

src/libraries/System.Runtime.Loader/tests/ApplyUpdateTest.cs

@@ -3,6 +3,7 @@
 
 using System.Reflection;
 using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
 using Xunit;
 
 namespace System.Reflection.Metadata
@@ -629,5 +630,87 @@ public static void TestReflectionAddNewType()
  System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewType.ZExistingClass.ExistingMethod ();
  });
  }
+
+ [ConditionalFact(typeof(ApplyUpdateUtil), nameof(ApplyUpdateUtil.IsSupported))]
+ public static void TestReflectionAddNewMethod()
+ {
+ ApplyUpdateUtil.TestCase(static () =>
+ {
+ var ty = typeof(System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod);
+ var assm = ty.Assembly;
+
+ var bindingFlags = BindingFlags.Instance | BindingFlags.Public;
+ var allMethods = ty.GetMethods(bindingFlags);
+
+ int objectMethods = typeof(object).GetMethods(bindingFlags).Length;
+ Assert.Equal (objectMethods + 1, allMethods.Length);
+
+ ApplyUpdateUtil.ApplyUpdate(assm);
+ ApplyUpdateUtil.ClearAllReflectionCaches();
+
+ ty = typeof(System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod);
+
+ allMethods = ty.GetMethods(bindingFlags);
+ Assert.Equal (objectMethods + 2, allMethods.Length);
+
+ var mi = ty.GetMethod ("AddedNewMethod");
+
+ Assert.NotNull (mi);
+
+ var retParm = mi.ReturnParameter;
+ Assert.NotNull (retParm);
+ Assert.NotNull (retParm.ParameterType);
+ Assert.Equal (-1, retParm.Position);
+
+ var retCas = retParm.GetCustomAttributes(false);
+ Assert.NotNull(retCas);
+ Assert.Equal(0, retCas.Length);
+
+ var parms = mi.GetParameters();
+ Assert.Equal (5, parms.Length);
+
+ int parmPos = 0;
+ foreach (var parm in parms)
+ {
+ Assert.NotNull(parm);
+ Assert.NotNull(parm.ParameterType);
+ Assert.Equal(parmPos, parm.Position);
+ Assert.NotNull(parm.Name);
+
+ var cas = parm.GetCustomAttributes(false);
+ foreach (var ca in cas) {
+ Assert.NotNull (ca);
+ }
+
+ parmPos++;
+ }
+
+ var parmAttrs = parms[4].GetCustomAttributes(false);
+ Assert.Equal (2, parmAttrs.Length);
+ bool foundCallerMemberName = false;
+ bool foundOptional = false;
+ foreach (var pa in parmAttrs) {
+ if (typeof (CallerMemberNameAttribute).Equals(pa.GetType()))
+ {
+ foundCallerMemberName = true;
+ }
+ if (typeof (OptionalAttribute).Equals(pa.GetType()))
+ {
+ foundOptional = true;
+ }
+ }
+ Assert.True(foundCallerMemberName);
+ Assert.True(foundOptional);
+
+ // n.b. this typeof() also makes the rest of the test work on Wasm with aggressive trimming.
+ Assert.Equal (typeof(System.Threading.CancellationToken), parms[3].ParameterType);
+
+ Assert.True(parms[3].HasDefaultValue);
+ Assert.True(parms[4].HasDefaultValue);
+
+ Assert.Null(parms[3].DefaultValue);
+ Assert.Equal(string.Empty, parms[4].DefaultValue);
+ });
+	} 
  }
 }

src/libraries/System.Runtime.Loader/tests/System.Runtime.Loader.Tests.csproj

@@ -62,6 +62,7 @@
  <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.AddStaticLambda\System.Reflection.Metadata.ApplyUpdate.Test.AddStaticLambda.csproj" />
  <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.StaticLambdaRegression\System.Reflection.Metadata.ApplyUpdate.Test.StaticLambdaRegression.csproj" />
  <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewType\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewType.csproj" />
+ <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod.csproj" />
  </ItemGroup>
  <ItemGroup Condition="'$(TargetOS)' == 'Browser'">
  <WasmFilesToIncludeFromPublishDir Include="$(AssemblyName).dll" />

src/mono/mono/component/hot_reload-internals.h

@@ -86,4 +86,9 @@ typedef struct _MonoClassMetadataUpdateEvent {
 	uint32_t token; /* the Event table token where this event was defined. */
 } MonoClassMetadataUpdateEvent;
 
+typedef struct _MonoMethodMetadataUpdateParamInfo {
+	uint32_t first_param_token; /* a Param token */
+	uint32_t param_count;
+} MonoMethodMetadataUpdateParamInfo;
+
 #endif/*_MONO_COMPONENT_HOT_RELOAD_INTERNALS_H*/

src/mono/mono/component/hot_reload-stub.c

@@ -110,6 +110,9 @@ hot_reload_get_num_methods_added (MonoClass *klass);
 static const char *
 hot_reload_get_capabilities (void);
 
+static uint32_t
+hot_reload_stub_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt);
+
 static MonoComponentHotReload fn_table = {
 	{ MONO_COMPONENT_ITF_VERSION, &hot_reload_stub_available },
 	&hot_reload_stub_set_fastpath_data,
@@ -142,7 +145,8 @@ static MonoComponentHotReload fn_table = {
 	&hot_reload_stub_added_fields_iter,
 	&hot_reload_get_num_fields_added,
 	&hot_reload_get_num_methods_added,
-	&hot_reload_get_capabilities
+	&hot_reload_get_capabilities,
+	&hot_reload_stub_get_method_params,
 };
 
 static bool
@@ -343,6 +347,12 @@ hot_reload_get_capabilities (void)
 	return "";
 }
 
+static uint32_t
+hot_reload_stub_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt)
+{
+	return 0;
+}
+
 MONO_COMPONENT_EXPORT_ENTRYPOINT
 MonoComponentHotReload *
 mono_component_hot_reload_init (void)

src/mono/mono/component/hot_reload.c

@@ -144,6 +144,9 @@ hot_reload_get_num_methods_added (MonoClass *klass);
 static const char *
 hot_reload_get_capabilities (void);
 
+static uint32_t
+hot_reload_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt);
+
 static MonoClassMetadataUpdateField *
 metadata_update_field_setup_basic_info (MonoImage *image_base, BaselineInfo *base_info, uint32_t generation, DeltaInfo *delta_info, MonoClass *parent_klass, uint32_t fielddef_token, uint32_t field_flags);
 
@@ -179,7 +182,8 @@ static MonoComponentHotReload fn_table = {
 	&hot_reload_added_fields_iter,
 	&hot_reload_get_num_fields_added,
 	&hot_reload_get_num_methods_added,
-	&hot_reload_get_capabilities
+	&hot_reload_get_capabilities,
+	&hot_reload_get_method_params,
 };
 
 MonoComponentHotReload *
@@ -272,6 +276,9 @@ struct _BaselineInfo {
 	/* Parents for added methods, fields, etc */
 	GHashTable *member_parent; /* maps added methoddef or fielddef tokens to typedef tokens */
 
+	/* Params for added methods */
+	GHashTable *method_params; /* maps methoddef tokens to a MonoClassMetadataUpdateMethodParamInfo* */
+
 	/* Skeletons for all newly-added types from every generation. Accessing the array requires the image lock. */
 	GArray *skeletons;
 };
@@ -412,6 +419,12 @@ baseline_info_destroy (BaselineInfo *info)
 	if (info->skeletons)
  g_array_free (info->skeletons, TRUE);
 
+	if (info->member_parent)
+ g_hash_table_destroy (info->member_parent);
+
+	if (info->method_params)
+ g_hash_table_destroy (info->method_params);
+
 	g_free (info);
 }
 
@@ -627,6 +640,11 @@ add_method_to_baseline (BaselineInfo *base_info, DeltaInfo *delta_info, MonoClas
 static void
 add_field_to_baseline (BaselineInfo *base_info, DeltaInfo *delta_info, MonoClass *klass, uint32_t field_token);
 
+/* Add a method->params lookup for new methods in existing classes */
+static void
+add_param_info_for_method (BaselineInfo *base_info, uint32_t param_token, uint32_t method_token);
+
+
 void
 hot_reload_init (void)
 {
@@ -2019,6 +2037,7 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
 	uint32_t add_member_typedef = 0;
 	uint32_t add_property_propertymap = 0;
 	uint32_t add_event_eventmap = 0;
+	uint32_t add_field_method = 0;
 
 	gboolean assemblyref_updated = FALSE;
 	for (guint32 i = 0; i < rows ; ++i) {
@@ -2049,6 +2068,7 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
 
  case ENC_FUNC_ADD_PARAM: {
  g_assert (token_table == MONO_TABLE_METHOD);
+ add_field_method = log_token;
  break;
  }
  case ENC_FUNC_ADD_FIELD: {
@@ -2115,8 +2135,11 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
  }
  case MONO_TABLE_METHOD: {
  /* if adding a param, handle it with the next record */
- if (func_code == ENC_FUNC_ADD_PARAM)
+ if (func_code == ENC_FUNC_ADD_PARAM) {
+ g_assert (is_addition);
  break;
+ }
+ g_assert (func_code == ENC_FUNC_DEFAULT);
 
  if (!base_info->method_table_update)
  base_info->method_table_update = g_hash_table_new (g_direct_hash, g_direct_equal);
@@ -2366,9 +2389,21 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
  *
  * So by the time we see the param additions, the methods are already in.
  *
- * FIXME: we need a lookaside table (like member_parent) for every place
- * that looks at MONO_METHOD_PARAMLIST
  */
+ if (is_addition) {
+ g_assert (add_field_method != 0);
+ uint32_t parent_type_token = hot_reload_method_parent (image_base, add_field_method);
+ g_assert (parent_type_token != 0); // we added a parameter to a method that was added
+ if (pass2_context_is_skeleton (ctx, parent_type_token)) {
+ // it's a parameter on a new method in a brand new class
+ // FIXME: need to do something here?
+ } else {
+ // it's a parameter on a new method in an existing class
+ add_param_info_for_method (base_info, log_token, add_field_method);
+ }
+ add_field_method = 0;
+ break;
+ }
  break;
  }
  case MONO_TABLE_INTERFACEIMPL: {
@@ -2819,6 +2854,28 @@ hot_reload_field_parent (MonoImage *base_image, uint32_t field_token)
 }
 
 
+static void
+add_param_info_for_method (BaselineInfo *base_info, uint32_t param_token, uint32_t method_token)
+{
+	if (!base_info->method_params) {
+ base_info->method_params = g_hash_table_new_full (g_direct_hash, g_direct_equal, NULL, g_free);
+	}
+	MonoMethodMetadataUpdateParamInfo* info = NULL;
+	info = g_hash_table_lookup (base_info->method_params, GUINT_TO_POINTER (method_token));
+	if (!info) {
+ // FIXME locking
+ info = g_new0 (MonoMethodMetadataUpdateParamInfo, 1);
+ g_hash_table_insert (base_info->method_params, GUINT_TO_POINTER (method_token), info);
+ info->first_param_token = param_token;
+ info->param_count = 1;
+	} else {
+ uint32_t param_index = mono_metadata_token_index (param_token);
+ // expect params for a single method to be a contiguous sequence of rows
+ g_assert (mono_metadata_token_index (info->first_param_token) + info->param_count == param_index);
+ info->param_count++;
+	}
+}
+
 /* HACK - keep in sync with locator_t in metadata/metadata.c */
 typedef struct {
 	guint32 idx; /* The index that we are trying to locate */
@@ -3148,6 +3205,32 @@ hot_reload_get_num_methods_added (MonoClass *klass)
 	return count;
 }
 
+static uint32_t
+hot_reload_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt)
+{
+	BaselineInfo *base_info = baseline_info_lookup (base_image);
+	g_assert (base_info);
+
+	/* FIXME: locking in case the hash table grows */
+
+	if (!base_info->method_params)
+ return 0;
+
+	MonoMethodMetadataUpdateParamInfo* info = NULL;
+	info = g_hash_table_lookup (base_info->method_params, GUINT_TO_POINTER (methoddef_token));
+	if (!info) {
+ if (out_param_count_opt)
+ *out_param_count_opt = 0;
+ return 0;
+	}
+
+	if (out_param_count_opt)
+ *out_param_count_opt = info->param_count;
+
+	return mono_metadata_token_index (info->first_param_token);
+}
+
+
 static const char *
 hot_reload_get_capabilities (void)
 {

src/mono/mono/component/hot_reload.h

@@ -48,6 +48,7 @@ typedef struct _MonoComponentHotReload {
 	uint32_t (*get_num_fields_added) (MonoClass *klass);
 	uint32_t (*get_num_methods_added) (MonoClass *klass);
 	const char* (*get_capabilities) (void);
+	uint32_t (*get_method_params) (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt);
 } MonoComponentHotReload;
 
 MONO_COMPONENT_EXPORT_ENTRYPOINT

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/ReflectionAddNewMethod.cs

@@ -0,0 +1,16 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+using System;
+
+
+namespace System.Reflection.Metadata.ApplyUpdate.Test
+{
+ public class ReflectionAddNewMethod
+ {
+ public string ExistingMethod(string u, double f)
+	{
+ return u + f.ToString();;
+ }
+
+ }
+}

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/ReflectionAddNewMethod_v1.cs

@@ -0,0 +1,21 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+using System;
+using System.Runtime.CompilerServices;
+using CancellationToken = System.Threading.CancellationToken;
+
+namespace System.Reflection.Metadata.ApplyUpdate.Test
+{
+ public class ReflectionAddNewMethod
+ {
+ public string ExistingMethod(string u, double f)
+	{
+ return u + f.ToString();;
+ }
+
+	public double AddedNewMethod(char c, float h, string w, CancellationToken ct = default, [CallerMemberName] string callerName = "")
+	{
+ return ((double)Convert.ToInt32(c)) + h;
+	}
+ }
+}

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod.csproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+ <PropertyGroup>
+ <RootNamespace>System.Runtime.Loader.Tests</RootNamespace>
+ <TargetFramework>$(NetCoreAppCurrent)</TargetFramework>
+ <TestRuntime>true</TestRuntime>
+ <DeltaScript>deltascript.json</DeltaScript>
+ </PropertyGroup>
+ <ItemGroup>
+ <Compile Include="ReflectionAddNewMethod.cs" />
+ </ItemGroup>
+</Project>

src/libraries/System.Runtime.Loader/tests/ApplyUpdate/System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod/deltascript.json

@@ -0,0 +1,6 @@
+{
+ "changes": [
+ {"document": "ReflectionAddNewMethod.cs", "update": "ReflectionAddNewMethod_v1.cs"},
+ ]
+}
+

src/libraries/System.Runtime.Loader/tests/ApplyUpdateTest.cs

@@ -3,6 +3,7 @@
 
 using System.Reflection;
 using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
 using Xunit;
 
 namespace System.Reflection.Metadata
@@ -629,5 +630,87 @@ public static void TestReflectionAddNewType()
  System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewType.ZExistingClass.ExistingMethod ();
  });
  }
+
+ [ConditionalFact(typeof(ApplyUpdateUtil), nameof(ApplyUpdateUtil.IsSupported))]
+ public static void TestReflectionAddNewMethod()
+ {
+ ApplyUpdateUtil.TestCase(static () =>
+ {
+ var ty = typeof(System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod);
+ var assm = ty.Assembly;
+
+ var bindingFlags = BindingFlags.Instance | BindingFlags.Public;
+ var allMethods = ty.GetMethods(bindingFlags);
+
+ int objectMethods = typeof(object).GetMethods(bindingFlags).Length;
+ Assert.Equal (objectMethods + 1, allMethods.Length);
+
+ ApplyUpdateUtil.ApplyUpdate(assm);
+ ApplyUpdateUtil.ClearAllReflectionCaches();
+
+ ty = typeof(System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod);
+
+ allMethods = ty.GetMethods(bindingFlags);
+ Assert.Equal (objectMethods + 2, allMethods.Length);
+
+ var mi = ty.GetMethod ("AddedNewMethod");
+
+ Assert.NotNull (mi);
+
+ var retParm = mi.ReturnParameter;
+ Assert.NotNull (retParm);
+ Assert.NotNull (retParm.ParameterType);
+ Assert.Equal (-1, retParm.Position);
+
+ var retCas = retParm.GetCustomAttributes(false);
+ Assert.NotNull(retCas);
+ Assert.Equal(0, retCas.Length);
+
+ var parms = mi.GetParameters();
+ Assert.Equal (5, parms.Length);
+
+ int parmPos = 0;
+ foreach (var parm in parms)
+ {
+ Assert.NotNull(parm);
+ Assert.NotNull(parm.ParameterType);
+ Assert.Equal(parmPos, parm.Position);
+ Assert.NotNull(parm.Name);
+
+ var cas = parm.GetCustomAttributes(false);
+ foreach (var ca in cas) {
+ Assert.NotNull (ca);
+ }
+
+ parmPos++;
+ }
+
+ var parmAttrs = parms[4].GetCustomAttributes(false);
+ Assert.Equal (2, parmAttrs.Length);
+ bool foundCallerMemberName = false;
+ bool foundOptional = false;
+ foreach (var pa in parmAttrs) {
+ if (typeof (CallerMemberNameAttribute).Equals(pa.GetType()))
+ {
+ foundCallerMemberName = true;
+ }
+ if (typeof (OptionalAttribute).Equals(pa.GetType()))
+ {
+ foundOptional = true;
+ }
+ }
+ Assert.True(foundCallerMemberName);
+ Assert.True(foundOptional);
+
+ // n.b. this typeof() also makes the rest of the test work on Wasm with aggressive trimming.
+ Assert.Equal (typeof(System.Threading.CancellationToken), parms[3].ParameterType);
+
+ Assert.True(parms[3].HasDefaultValue);
+ Assert.True(parms[4].HasDefaultValue);
+
+ Assert.Null(parms[3].DefaultValue);
+ Assert.Equal(string.Empty, parms[4].DefaultValue);
+ });
+	} 
  }
 }

src/libraries/System.Runtime.Loader/tests/System.Runtime.Loader.Tests.csproj

@@ -62,6 +62,7 @@
  <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.AddStaticLambda\System.Reflection.Metadata.ApplyUpdate.Test.AddStaticLambda.csproj" />
  <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.StaticLambdaRegression\System.Reflection.Metadata.ApplyUpdate.Test.StaticLambdaRegression.csproj" />
  <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewType\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewType.csproj" />
+ <ProjectReference Include="ApplyUpdate\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod\System.Reflection.Metadata.ApplyUpdate.Test.ReflectionAddNewMethod.csproj" />
  </ItemGroup>
  <ItemGroup Condition="'$(TargetOS)' == 'Browser'">
  <WasmFilesToIncludeFromPublishDir Include="$(AssemblyName).dll" />

src/mono/mono/component/hot_reload-internals.h

@@ -86,4 +86,9 @@ typedef struct _MonoClassMetadataUpdateEvent {
 	uint32_t token; /* the Event table token where this event was defined. */
 } MonoClassMetadataUpdateEvent;
 
+typedef struct _MonoMethodMetadataUpdateParamInfo {
+	uint32_t first_param_token; /* a Param token */
+	uint32_t param_count;
+} MonoMethodMetadataUpdateParamInfo;
+
 #endif/*_MONO_COMPONENT_HOT_RELOAD_INTERNALS_H*/

src/mono/mono/component/hot_reload-stub.c

@@ -110,6 +110,9 @@ hot_reload_get_num_methods_added (MonoClass *klass);
 static const char *
 hot_reload_get_capabilities (void);
 
+static uint32_t
+hot_reload_stub_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt);
+
 static MonoComponentHotReload fn_table = {
 	{ MONO_COMPONENT_ITF_VERSION, &hot_reload_stub_available },
 	&hot_reload_stub_set_fastpath_data,
@@ -142,7 +145,8 @@ static MonoComponentHotReload fn_table = {
 	&hot_reload_stub_added_fields_iter,
 	&hot_reload_get_num_fields_added,
 	&hot_reload_get_num_methods_added,
-	&hot_reload_get_capabilities
+	&hot_reload_get_capabilities,
+	&hot_reload_stub_get_method_params,
 };
 
 static bool
@@ -343,6 +347,12 @@ hot_reload_get_capabilities (void)
 	return "";
 }
 
+static uint32_t
+hot_reload_stub_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt)
+{
+	return 0;
+}
+
 MONO_COMPONENT_EXPORT_ENTRYPOINT
 MonoComponentHotReload *
 mono_component_hot_reload_init (void)

src/mono/mono/component/hot_reload.c

@@ -144,6 +144,9 @@ hot_reload_get_num_methods_added (MonoClass *klass);
 static const char *
 hot_reload_get_capabilities (void);
 
+static uint32_t
+hot_reload_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt);
+
 static MonoClassMetadataUpdateField *
 metadata_update_field_setup_basic_info (MonoImage *image_base, BaselineInfo *base_info, uint32_t generation, DeltaInfo *delta_info, MonoClass *parent_klass, uint32_t fielddef_token, uint32_t field_flags);
 
@@ -179,7 +182,8 @@ static MonoComponentHotReload fn_table = {
 	&hot_reload_added_fields_iter,
 	&hot_reload_get_num_fields_added,
 	&hot_reload_get_num_methods_added,
-	&hot_reload_get_capabilities
+	&hot_reload_get_capabilities,
+	&hot_reload_get_method_params,
 };
 
 MonoComponentHotReload *
@@ -272,6 +276,9 @@ struct _BaselineInfo {
 	/* Parents for added methods, fields, etc */
 	GHashTable *member_parent; /* maps added methoddef or fielddef tokens to typedef tokens */
 
+	/* Params for added methods */
+	GHashTable *method_params; /* maps methoddef tokens to a MonoClassMetadataUpdateMethodParamInfo* */
+
 	/* Skeletons for all newly-added types from every generation. Accessing the array requires the image lock. */
 	GArray *skeletons;
 };
@@ -412,6 +419,12 @@ baseline_info_destroy (BaselineInfo *info)
 	if (info->skeletons)
  g_array_free (info->skeletons, TRUE);
 
+	if (info->member_parent)
+ g_hash_table_destroy (info->member_parent);
+
+	if (info->method_params)
+ g_hash_table_destroy (info->method_params);
+
 	g_free (info);
 }
 
@@ -627,6 +640,11 @@ add_method_to_baseline (BaselineInfo *base_info, DeltaInfo *delta_info, MonoClas
 static void
 add_field_to_baseline (BaselineInfo *base_info, DeltaInfo *delta_info, MonoClass *klass, uint32_t field_token);
 
+/* Add a method->params lookup for new methods in existing classes */
+static void
+add_param_info_for_method (BaselineInfo *base_info, uint32_t param_token, uint32_t method_token);
+
+
 void
 hot_reload_init (void)
 {
@@ -2019,6 +2037,7 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
 	uint32_t add_member_typedef = 0;
 	uint32_t add_property_propertymap = 0;
 	uint32_t add_event_eventmap = 0;
+	uint32_t add_field_method = 0;
 
 	gboolean assemblyref_updated = FALSE;
 	for (guint32 i = 0; i < rows ; ++i) {
@@ -2049,6 +2068,7 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
 
  case ENC_FUNC_ADD_PARAM: {
  g_assert (token_table == MONO_TABLE_METHOD);
+ add_field_method = log_token;
  break;
  }
  case ENC_FUNC_ADD_FIELD: {
@@ -2115,8 +2135,11 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
  }
  case MONO_TABLE_METHOD: {
  /* if adding a param, handle it with the next record */
- if (func_code == ENC_FUNC_ADD_PARAM)
+ if (func_code == ENC_FUNC_ADD_PARAM) {
+ g_assert (is_addition);
  break;
+ }
+ g_assert (func_code == ENC_FUNC_DEFAULT);
 
  if (!base_info->method_table_update)
  base_info->method_table_update = g_hash_table_new (g_direct_hash, g_direct_equal);
@@ -2366,9 +2389,21 @@ apply_enclog_pass2 (Pass2Context *ctx, MonoImage *image_base, BaselineInfo *base
  *
  * So by the time we see the param additions, the methods are already in.
  *
- * FIXME: we need a lookaside table (like member_parent) for every place
- * that looks at MONO_METHOD_PARAMLIST
  */
+ if (is_addition) {
+ g_assert (add_field_method != 0);
+ uint32_t parent_type_token = hot_reload_method_parent (image_base, add_field_method);
+ g_assert (parent_type_token != 0); // we added a parameter to a method that was added
+ if (pass2_context_is_skeleton (ctx, parent_type_token)) {
+ // it's a parameter on a new method in a brand new class
+ // FIXME: need to do something here?
+ } else {
+ // it's a parameter on a new method in an existing class
+ add_param_info_for_method (base_info, log_token, add_field_method);
+ }
+ add_field_method = 0;
+ break;
+ }
  break;
  }
  case MONO_TABLE_INTERFACEIMPL: {
@@ -2819,6 +2854,28 @@ hot_reload_field_parent (MonoImage *base_image, uint32_t field_token)
 }
 
 
+static void
+add_param_info_for_method (BaselineInfo *base_info, uint32_t param_token, uint32_t method_token)
+{
+	if (!base_info->method_params) {
+ base_info->method_params = g_hash_table_new_full (g_direct_hash, g_direct_equal, NULL, g_free);
+	}
+	MonoMethodMetadataUpdateParamInfo* info = NULL;
+	info = g_hash_table_lookup (base_info->method_params, GUINT_TO_POINTER (method_token));
+	if (!info) {
+ // FIXME locking
+ info = g_new0 (MonoMethodMetadataUpdateParamInfo, 1);
+ g_hash_table_insert (base_info->method_params, GUINT_TO_POINTER (method_token), info);
+ info->first_param_token = param_token;
+ info->param_count = 1;
+	} else {
+ uint32_t param_index = mono_metadata_token_index (param_token);
+ // expect params for a single method to be a contiguous sequence of rows
+ g_assert (mono_metadata_token_index (info->first_param_token) + info->param_count == param_index);
+ info->param_count++;
+	}
+}
+
 /* HACK - keep in sync with locator_t in metadata/metadata.c */
 typedef struct {
 	guint32 idx; /* The index that we are trying to locate */
@@ -3148,6 +3205,32 @@ hot_reload_get_num_methods_added (MonoClass *klass)
 	return count;
 }
 
+static uint32_t
+hot_reload_get_method_params (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt)
+{
+	BaselineInfo *base_info = baseline_info_lookup (base_image);
+	g_assert (base_info);
+
+	/* FIXME: locking in case the hash table grows */
+
+	if (!base_info->method_params)
+ return 0;
+
+	MonoMethodMetadataUpdateParamInfo* info = NULL;
+	info = g_hash_table_lookup (base_info->method_params, GUINT_TO_POINTER (methoddef_token));
+	if (!info) {
+ if (out_param_count_opt)
+ *out_param_count_opt = 0;
+ return 0;
+	}
+
+	if (out_param_count_opt)
+ *out_param_count_opt = info->param_count;
+
+	return mono_metadata_token_index (info->first_param_token);
+}
+
+
 static const char *
 hot_reload_get_capabilities (void)
 {

src/mono/mono/component/hot_reload.h

@@ -48,6 +48,7 @@ typedef struct _MonoComponentHotReload {
 	uint32_t (*get_num_fields_added) (MonoClass *klass);
 	uint32_t (*get_num_methods_added) (MonoClass *klass);
 	const char* (*get_capabilities) (void);
+	uint32_t (*get_method_params) (MonoImage *base_image, uint32_t methoddef_token, uint32_t *out_param_count_opt);
 } MonoComponentHotReload;
 
 MONO_COMPONENT_EXPORT_ENTRYPOINT