[wasm][debugger] For some types, use `ToString()` for their ..

.. `description`.

- `System.DateTime`
- `System.DateTimeOffset`
- `System.Decimal`
- `System.TimeSpan`
- `System.Guid`

4 files changed, 278 insertions, 26 deletions

diff --git a/mono/mini/mini-wasm-debugger.c b/mono/mini/mini-wasm-debugger.c
index 737028ff611..8586a2e2819 100644
--- a/mono/mini/mini-wasm-debugger.c
+++ b/mono/mini/mini-wasm-debugger.c
@@ -44,9 +44,9 @@ extern void mono_wasm_fire_bp (void);
 extern void mono_wasm_add_bool_var (gint8);
 extern void mono_wasm_add_number_var (double);
 extern void mono_wasm_add_string_var (const char*);
-extern void mono_wasm_add_obj_var (const char*, guint64);
-extern void mono_wasm_add_value_type_unexpanded_var (const char*);
-extern void mono_wasm_begin_value_type_var (const char*);
+extern void mono_wasm_add_obj_var (const char*, const char*, guint64);
+extern void mono_wasm_add_value_type_unexpanded_var (const char*, const char*);
+extern void mono_wasm_begin_value_type_var (const char*, const char*);
 extern void mono_wasm_end_value_type_var (void);
 extern void mono_wasm_add_enum_var (const char*, const char*, guint64);
 extern void mono_wasm_add_func_var (const char*, guint64);
@@ -67,6 +67,15 @@ static GHashTable *objrefs;
 static GHashTable *obj_to_objref;
 static int objref_id = 0;
 
+static const char*
+to_string_as_descr_names[] = {
+	"System.DateTime",
+	"System.DateTimeOffset",
+	"System.Decimal",
+	"System.TimeSpan",
+	"System.Guid"
+};
+
 #define THREAD_TO_INTERNAL(thread) (thread)->internal_thread
 
 static void
@@ -616,6 +625,62 @@ mono_wasm_enum_frames (void)
 	mono_walk_stack_with_ctx (list_frames, NULL, MONO_UNWIND_NONE, NULL);
 }
 
+static char*
+invoke_to_string (MonoClass *klass, gpointer addr)
+{
+	MonoObject *exc;
+	MonoString *mstr;
+	char *ret_str;
+	ERROR_DECL (error);
+	MonoObject *obj;
+
+	// TODO: this is for a specific use case right now,
+	//       (invoke ToString() get a preview/description for *some* types)
+	//       and we don't want to report errors for that.
+	if (m_class_is_valuetype (klass)) {
+		MonoObject *boxed_obj = mono_value_box_checked (mono_domain_get (), klass, addr, error);
+		if (!is_ok (error))
+			return NULL;
+
+		obj = boxed_obj;
+	} else {
+		obj = *(MonoObject**)addr;
+	}
+
+	if (!obj)
+		return NULL;
+
+	mstr = mono_object_try_to_string (obj, &exc, error);
+	if (exc)
+		return NULL;
+
+	if (!is_ok (error))
+		return NULL;
+
+	ret_str = mono_string_to_utf8_checked_internal (mstr, error);
+	if (!is_ok (error))
+		return NULL;
+
+	// FREE boxed_obj
+
+	return ret_str;
+}
+
+static char*
+get_to_string_description (const char* class_name, MonoClass *klass, gpointer addr)
+{
+	if (!class_name || !klass || !addr)
+		return NULL;
+
+	for (int i = 0; i < G_N_ELEMENTS (to_string_as_descr_names); i ++) {
+		if (strcmp (to_string_as_descr_names [i], class_name) == 0) {
+			return invoke_to_string (klass, addr);
+		}
+	}
+
+	return NULL;
+}
+
 typedef struct {
 	int cur_frame;
 	int target_frame;
@@ -734,7 +799,9 @@ static gboolean describe_value(MonoType * type, gpointer addr, gboolean expandVa
 			} else if (m_class_is_delegate (klass)) {
 				mono_wasm_add_func_var (class_name, obj_id);
 			} else {
-				mono_wasm_add_obj_var (class_name, obj_id);
+				char *to_string_val = get_to_string_description (class_name, klass, addr);
+				mono_wasm_add_obj_var (class_name, to_string_val, obj_id);
+				g_free (to_string_val);
 			}
 			g_free (class_name);
 			break;
@@ -779,12 +846,17 @@ static gboolean describe_value(MonoType * type, gpointer addr, gboolean expandVa
 				mono_wasm_add_enum_var (class_name, enum_members->str, value__);
 				g_string_free (enum_members, TRUE);
 			} else if (expandValueType) {
-				mono_wasm_begin_value_type_var (class_name);
+				char *to_string_val = get_to_string_description (class_name, klass, addr);
+				mono_wasm_begin_value_type_var (class_name, to_string_val);
+				g_free (to_string_val);
+
 				// FIXME: isAsyncLocalThis
 				describe_object_properties_for_klass ((MonoObject*)addr, klass, FALSE, expandValueType);
 				mono_wasm_end_value_type_var ();
 			} else {
-				mono_wasm_add_value_type_unexpanded_var (class_name);
+				char *to_string_val = get_to_string_description (class_name, klass, addr);
+				mono_wasm_add_value_type_unexpanded_var (class_name, to_string_val);
+				g_free (to_string_val);
 			}
 			g_free (class_name);
 			break;
@@ -975,7 +1047,7 @@ describe_non_async_this (InterpFrame *frame, MonoMethod *method)
 		char *class_name = mono_class_full_name (obj->vtable->klass);
 
 		mono_wasm_add_properties_var ("this", -1);
-		mono_wasm_add_obj_var (class_name, get_object_id(obj));
+		mono_wasm_add_obj_var (class_name, NULL, get_object_id(obj));
 		g_free (class_name);
 	}
 }
diff --git a/sdks/wasm/DebuggerTestSuite/Tests.cs b/sdks/wasm/DebuggerTestSuite/Tests.cs
index 7da8614eb2f..ea0b6fc782e 100644
--- a/sdks/wasm/DebuggerTestSuite/Tests.cs
+++ b/sdks/wasm/DebuggerTestSuite/Tests.cs
@@ -251,7 +251,12 @@ namespace DebuggerTests
 		}
 
 		async Task CheckDateTime (JToken locals, string name, DateTime expected)
-			=> await CheckObjectOnLocals (locals, name,
+		{
+			var obj = locals.Where (jt => jt ["name"]?.Value<string> () == name)
+					.FirstOrDefault ();
+			Assert.Equal (expected.ToString (), obj ["value"]? ["description"]?.Value<string> ());
+
+			await CheckObjectOnLocals (locals, name,
 				test_fn: (members) => {
 					// not checking everything
 #if false
@@ -273,6 +278,7 @@ namespace DebuggerTests
 					// FIXME: check some float properties too
 				}
 			);
+		}
 
 		JToken CheckBool (JToken locals, string name, bool expected)
 		{
@@ -907,7 +913,7 @@ namespace DebuggerTests
 				var ss_local_props = await CompareObjectPropertiesOnFrameLocals (pause_location ["callFrames"][0], "ss_local",
 						new {
 							str_member = TString ("set in MethodWithLocalStructs#SimpleStruct#str_member"),
-							dt = TValueType ("System.DateTime"),
+							dt = TValueType ("System.DateTime", "2/3/2021 4:06:07 AM"),
 							gs = TValueType ("DebuggerTests.ValueTypesTest.GenericStruct<System.DateTime>"),
 							Kind = TEnum ("System.DateTimeKind", "Utc")
 						});
@@ -950,7 +956,7 @@ namespace DebuggerTests
 					await CompareObjectPropertiesFor (vt_local_props, "SimpleStructProperty", 
 						new {
 							str_member = TString ("SimpleStructProperty#string#0#SimpleStruct#str_member"),
-							dt = TValueType ("System.DateTime"),
+							dt = TValueType ("System.DateTime", "3/4/2022 5:07:08 AM"),
 							gs = TValueType ("DebuggerTests.ValueTypesTest.GenericStruct<System.DateTime>"),
 							Kind = TEnum ("System.DateTimeKind", "Utc")
 						},
@@ -959,7 +965,7 @@ namespace DebuggerTests
 					await CompareObjectPropertiesFor (vt_local_props, "SimpleStructField",
 						new {
 							str_member = TString ("SimpleStructField#string#0#SimpleStruct#str_member"),
-							dt = TValueType ("System.DateTime"),
+							dt = TValueType ("System.DateTime", "6/7/2025 8:10:11 AM"),
 							gs = TValueType ("DebuggerTests.ValueTypesTest.GenericStruct<System.DateTime>"),
 							Kind = TEnum ("System.DateTimeKind", "Local")
 						},
@@ -998,7 +1004,7 @@ namespace DebuggerTests
 
 				var ss_local_as_ss_arg = new {
 					str_member = TString    ("ss_local#SimpleStruct#string#0#SimpleStruct#str_member"),
-					dt         = TValueType ("System.DateTime"),
+					dt         = TValueType ("System.DateTime", "6/7/2025 8:10:11 AM"),
 					gs         = TValueType ("DebuggerTests.ValueTypesTest.GenericStruct<System.DateTime>"),
 					Kind       = TEnum      ("System.DateTimeKind", "Local")
 				};
@@ -1033,7 +1039,7 @@ namespace DebuggerTests
 
 				var ss_arg_updated = new {
 					str_member = TString    ("ValueTypesTest#MethodWithStructArgs#updated#ss_arg#str_member"),
-					dt         = TValueType ("System.DateTime"),
+					dt         = TValueType ("System.DateTime", "6/7/2025 8:10:11 AM"),
 					gs         = TValueType ("DebuggerTests.ValueTypesTest.GenericStruct<System.DateTime>"),
 					Kind       = TEnum      ("System.DateTimeKind", "Utc")
 				};
@@ -1119,7 +1125,7 @@ namespace DebuggerTests
 				var ss_local_props = await CompareObjectPropertiesOnFrameLocals (pause_location ["callFrames"][0], "ss_local",
 					new {
 						str_member = TString ("set in MethodWithLocalStructsStaticAsync#SimpleStruct#str_member"),
-						dt         = TValueType ("System.DateTime"),
+						dt         = TValueType ("System.DateTime", "2/3/2021 4:06:07 AM"),
 						gs         = TValueType ("DebuggerTests.ValueTypesTest.GenericStruct<System.DateTime>"),
 						Kind       = TEnum ("System.DateTimeKind", "Utc")
 					});
@@ -1650,6 +1656,74 @@ namespace DebuggerTests
 			});
 		}
 
+		[Theory]
+		[InlineData (123, 3, "MethodWithLocalsForToStringTest", false, false)]
+		[InlineData (133, 3, "MethodWithArgumentsForToStringTest", true, false)]
+		[InlineData (175, 3, "MethodWithArgumentsForToStringTestAsync", true, true)]
+		[InlineData (165, 3, "MethodWithArgumentsForToStringTestAsync", false, true)]
+		public async Task InspectLocalsForToStringDescriptions (int line, int col, string method_name, bool call_other, bool invoke_async)
+		{
+			var insp = new Inspector ();
+			//Collect events
+			var scripts = SubscribeToScripts(insp);
+			string entry_method_name = $"[debugger-test] DebuggerTests.ValueTypesTest:MethodWithLocalsForToStringTest{(invoke_async ? "Async" : String.Empty)}";
+			int frame_idx = 0;
+
+			await Ready();
+			await insp.Ready (async (cli, token) => {
+				ctx = new DebugTestContext (cli, insp, token, scripts);
+				var debugger_test_loc = "dotnet://debugger-test.dll/debugger-valuetypes-test.cs";
+
+				await SetBreakpoint (debugger_test_loc, line, col);
+
+				var eval_expr = "window.setTimeout(function() {"
+									+ (invoke_async ? "invoke_static_method_async (" : "invoke_static_method (")
+										+ $"'{entry_method_name}',"
+										+ (call_other ? "true" : "false")
+									+ "); }, 1);";
+				Console.WriteLine ($"{eval_expr}");
+
+				var pause_location = await EvaluateAndCheck (eval_expr, debugger_test_loc, line, col, invoke_async ? "MoveNext" : method_name);
+
+				var frame_locals = await CheckLocalsOnFrame (pause_location ["callFrames"][frame_idx],
+					new {
+						call_other     = TBool      (call_other),
+						dt0            = TValueType ("System.DateTime", "1/2/2020 3:04:05 AM"),
+						dt1            = TValueType ("System.DateTime", "5/4/2010 3:02:01 AM"),
+						dto            = TValueType ("System.DateTimeOffset", "1/2/2020 3:04:05 AM +04:05"),
+						ts             = TValueType ("System.TimeSpan", "3530.00:02:04"),
+						dec            = TValueType ("System.Decimal", "123987123"),
+						guid           = TValueType ("System.Guid", "3d36e07e-ac90-48c6-b7ec-a481e289d014"),
+						dts            = TArray     ("System.DateTime[]"),
+						obj            = TObject    ("DebuggerTests.ClassForToStringTests"),
+						sst            = TObject    ("DebuggerTests.StructForToStringTests")
+					},
+					"locals#0");
+
+				var dts_elements = await CheckObjectOnLocals (frame_locals, "dts");
+				await CheckDateTime (dts_elements, "[0]", new DateTime (1983, 6, 7, 5, 6, 10));
+				await CheckDateTime (dts_elements, "[1]", new DateTime (1999, 10, 15, 1, 2, 3));
+
+				var obj_props = await CompareObjectPropertiesFor (frame_locals, "obj",
+						new {
+							DT         = TValueType ("System.DateTime", "10/15/2004 1:02:03 AM"),
+							DTO        = TValueType ("System.DateTimeOffset", "1/2/2020 3:04:05 AM +02:14"),
+							TS         = TValueType ("System.TimeSpan", "3530.00:02:04"),
+							Dec        = TValueType ("System.Decimal", "1239871"),
+							Guid       = TValueType ("System.Guid", "3d36e07e-ac90-48c6-b7ec-a481e289d014")
+						}, "obj_props");
+
+				var sst_props = await CompareObjectPropertiesFor (frame_locals, "sst",
+						new {
+							DT         = TValueType ("System.DateTime", "10/15/2004 1:02:03 AM"),
+							DTO        = TValueType ("System.DateTimeOffset", "1/2/2020 3:04:05 AM +03:15"),
+							TS         = TValueType ("System.TimeSpan", "3530.00:02:04"),
+							Dec        = TValueType ("System.Decimal", "1239871"),
+							Guid       = TValueType ("System.Guid", "3d36e07e-ac90-48c6-b7ec-a481e289d014")
+						}, "sst_props");
+			});
+		}
+
 		[Fact]
 		public async Task EvaluateThisProperties ()
 		{
@@ -2044,7 +2118,7 @@ namespace DebuggerTests
 			}
 		}
 
-		async Task<JToken> CheckObjectOnLocals (JToken locals, string name, Action<JToken> test_fn)
+		async Task<JToken> CheckObjectOnLocals (JToken locals, string name, Action<JToken> test_fn = null)
 		{
 			var obj = locals.Where (jt => jt ["name"]?.Value<string> () == name)
 					.FirstOrDefault ();
@@ -2121,16 +2195,16 @@ namespace DebuggerTests
 		static JObject TNumber (int value) =>
 			JObject.FromObject (new { type = "number", value = @value.ToString (), description = value.ToString () });
 
-		static JObject TValueType (string className, object members = null) =>
-			JObject.FromObject (new { type = "object", isValueType = true, className = className, description = className });
+		static JObject TValueType (string className, string description = null, object members = null) =>
+			JObject.FromObject (new { type = "object", isValueType = true, className = className, description = description ?? className });
 
 		static JObject TEnum (string className, string descr, object members = null) =>
 			JObject.FromObject (new { type = "object", isEnum = true, className = className, description = descr });
 
-		static JObject TObject (string className, bool is_null = false) =>
+		static JObject TObject (string className, string description = null, bool is_null = false) =>
 			is_null
-				? JObject.FromObject (new { type = "object", className = className, description = className, subtype = is_null ? "null" : null })
-				: JObject.FromObject (new { type = "object", className = className, description = className });
+				? JObject.FromObject (new { type = "object", className = className, description = description ?? className, subtype = is_null ? "null" : null })
+				: JObject.FromObject (new { type = "object", className = className, description = description ?? className });
 
 		static JObject TArray (string className)
 			=> JObject.FromObject (new { type = "object", className = className, description = className, subtype = "array" });
@@ -2138,6 +2212,9 @@ namespace DebuggerTests
 		static JObject TBool (bool value)
 			=> JObject.FromObject (new { type = "boolean", value = @value, description = @value ? "true" : "false" });
 
+		static JObject TSymbol (string value)
+			=> JObject.FromObject (new { type = "symbol", value = @value, description = @value });
+
 		//TODO add tests covering basic stepping behavior as step in/out/over
 	}
 
diff --git a/sdks/wasm/debugger-valuetypes-test.cs b/sdks/wasm/debugger-valuetypes-test.cs
index 58a15478f4d..9d1ee58d0f8 100644
--- a/sdks/wasm/debugger-valuetypes-test.cs
+++ b/sdks/wasm/debugger-valuetypes-test.cs
@@ -91,6 +91,109 @@ namespace DebuggerTests {
 
 		public DateTime DT { get; set; }
 		public RGB RGB;
+
+		public static void MethodWithLocalsForToStringTest (bool call_other)
+		{
+			var dt0 = new DateTime (2020, 1, 2, 3, 4, 5);
+			var dt1 = new DateTime (2010, 5, 4, 3, 2, 1);
+			var ts = dt0 - dt1;
+			var dto = new DateTimeOffset (dt0, new TimeSpan(4, 5, 0));
+			decimal dec = 123987123;
+			var guid = new Guid ("3d36e07e-ac90-48c6-b7ec-a481e289d014");
+
+			var dts = new DateTime [] {
+				new DateTime (1983, 6, 7, 5, 6, 10),
+				new DateTime (1999, 10, 15, 1, 2, 3)
+			};
+
+			var obj = new ClassForToStringTests {
+				DT = new DateTime (2004, 10, 15, 1, 2, 3),
+				DTO = new DateTimeOffset (dt0, new TimeSpan(2, 14, 0)),
+				TS = ts,
+				Dec = 1239871,
+				Guid = guid
+			};
+
+			var sst = new StructForToStringTests {
+				DT = new DateTime (2004, 10, 15, 1, 2, 3),
+				DTO = new DateTimeOffset (dt0, new TimeSpan (3, 15, 0)),
+				TS = ts,
+				Dec = 1239871,
+				Guid = guid
+			};
+			Console.WriteLine ($"MethodWithLocalsForToStringTest: {dt0}, {dt1}, {ts}, {dec}, {guid}, {dts[0]}, {obj.DT}, {sst.DT}");
+			if (call_other)
+				MethodWithArgumentsForToStringTest (call_other, dt0, dt1, ts, dto, dec, guid, dts, obj, sst);
+		}
+
+		static void MethodWithArgumentsForToStringTest (
+			bool call_other, // not really used, just to help with using common code in the tests
+			DateTime dt0, DateTime dt1, TimeSpan ts, DateTimeOffset dto, decimal dec,
+			Guid guid, DateTime[] dts, ClassForToStringTests obj, StructForToStringTests sst)
+		{
+			Console.WriteLine ($"MethodWithArgumentsForToStringTest: {dt0}, {dt1}, {ts}, {dec}, {guid}, {dts[0]}, {obj.DT}, {sst.DT}");
+		}
+
+		public static async Task MethodWithLocalsForToStringTestAsync (bool call_other)
+		{
+			var dt0 = new DateTime (2020, 1, 2, 3, 4, 5);
+			var dt1 = new DateTime (2010, 5, 4, 3, 2, 1);
+			var ts = dt0 - dt1;
+			var dto = new DateTimeOffset (dt0, new TimeSpan(4, 5, 0));
+			decimal dec = 123987123;
+			var guid = new Guid ("3d36e07e-ac90-48c6-b7ec-a481e289d014");
+
+			var dts = new DateTime [] {
+				new DateTime (1983, 6, 7, 5, 6, 10),
+				new DateTime (1999, 10, 15, 1, 2, 3)
+			};
+
+			var obj = new ClassForToStringTests {
+				DT = new DateTime (2004, 10, 15, 1, 2, 3),
+				DTO = new DateTimeOffset (dt0, new TimeSpan(2, 14, 0)),
+				TS = ts,
+				Dec = 1239871,
+				Guid = guid
+			};
+
+			var sst = new StructForToStringTests {
+				DT = new DateTime (2004, 10, 15, 1, 2, 3),
+				DTO = new DateTimeOffset (dt0, new TimeSpan (3, 15, 0)),
+				TS = ts,
+				Dec = 1239871,
+				Guid = guid
+			};
+			Console.WriteLine ($"MethodWithLocalsForToStringTest: {dt0}, {dt1}, {ts}, {dec}, {guid}, {dts[0]}, {obj.DT}, {sst.DT}");
+			if (call_other)
+				await MethodWithArgumentsForToStringTestAsync (call_other, dt0, dt1, ts, dto, dec, guid, dts, obj, sst);
+		}
+
+		static async Task MethodWithArgumentsForToStringTestAsync (
+			bool call_other, // not really used, just to help with using common code in the tests
+			DateTime dt0, DateTime dt1, TimeSpan ts, DateTimeOffset dto, decimal dec,
+			Guid guid, DateTime[] dts, ClassForToStringTests obj, StructForToStringTests sst)
+		{
+			Console.WriteLine ($"MethodWithArgumentsForToStringTest: {dt0}, {dt1}, {ts}, {dec}, {guid}, {dts[0]}, {obj.DT}, {sst.DT}");
+		}
+
+	}
+
+	class ClassForToStringTests
+	{
+		public DateTime DT;
+		public DateTimeOffset DTO;
+		public TimeSpan TS;
+		public decimal Dec;
+		public Guid Guid;
+	}
+
+	struct StructForToStringTests
+	{
+		public DateTime DT;
+		public DateTimeOffset DTO;
+		public TimeSpan TS;
+		public decimal Dec;
+		public Guid Guid;
 	}
 
 	public enum RGB
diff --git a/sdks/wasm/src/library_mono.js b/sdks/wasm/src/library_mono.js
index 65f6d16be32..fdf6fac6f4e 100644
--- a/sdks/wasm/src/library_mono.js
+++ b/sdks/wasm/src/library_mono.js
@@ -470,13 +470,13 @@ var MonoSupportLib = {
 		MONO._async_method_objectId = objectId;
 	},
 
-	mono_wasm_begin_value_type_var: function(className) {
+	mono_wasm_begin_value_type_var: function(className, toString) {
 		fixed_class_name = MONO._mono_csharp_fixup_class_name(Module.UTF8ToString (className));
 		var vt_obj = {
 			value: {
 				type: "object",
 				className: fixed_class_name,
-				description: fixed_class_name,
+				description: (toString == 0 ? fixed_class_name : Module.UTF8ToString (toString)),
 				// objectId will be generated by MonoProxy
 				expanded: true,
 				isValueType: true,
@@ -505,13 +505,13 @@ var MonoSupportLib = {
 		}
 	},
 
-	mono_wasm_add_value_type_unexpanded_var: function (className) {
+	mono_wasm_add_value_type_unexpanded_var: function (className, toString) {
 		fixed_class_name = MONO._mono_csharp_fixup_class_name(Module.UTF8ToString (className));
 		MONO.var_info.push({
 			value: {
 				type: "object",
 				className: fixed_class_name,
-				description: fixed_class_name,
+				description: (toString == 0 ? fixed_class_name : Module.UTF8ToString (toString)),
 				// objectId added when enumerating object's properties
 				expanded: false,
 				isValueType: true
@@ -563,7 +563,7 @@ var MonoSupportLib = {
 		});
 	},
 
-	mono_wasm_add_obj_var: function(className, objectId) {
+	mono_wasm_add_obj_var: function(className, toString, objectId) {
 		if (objectId == 0) {
 			MONO.mono_wasm_add_null_var (className);
 			return;
@@ -574,7 +574,7 @@ var MonoSupportLib = {
 			value: {
 				type: "object",
 				className: fixed_class_name,
-				description: fixed_class_name,
+				description: (toString == 0 ? fixed_class_name : Module.UTF8ToString (toString)),
 				objectId: "dotnet:object:"+ objectId,
 			}
 		});