sebastienros · lahma · Feb 7, 2026 · Jan 25, 2026
diff --git a/CLAUDE.md b/CLAUDE.md
@@ -128,6 +128,42 @@ Acornima Parser (external) → AST → Interpreter → Runtime → Interop
 - **Analysis**: Latest analyzers enabled with EnforceCodeStyleInBuild
 - **Performance**: Try to make code as perfomant as possible.
 
+### Data Structures
+
+**Prefer readonly record structs over tuples** for returning multiple values. Record structs provide better readability, named properties, and IDE support. Pass them into methods with 'in' modifier.
+
+```csharp
+// ❌ Avoid: Tuples with unnamed or poorly named fields
+public (JsPlainDate?, JsZonedDateTime?) GetRelativeTo(ObjectInstance options)
+{
+    // Item1 and Item2 are unclear at call site
+    return (plainDate, zonedDateTime);
+}
+
+// ✅ Prefer: readonly record struct with descriptive names
+[System.Runtime.InteropServices.StructLayout(LayoutKind.Auto)]
+public readonly record struct RelativeToResult(
+    JsPlainDate? PlainRelativeTo,
+    JsZonedDateTime? ZonedRelativeTo);
+
+public RelativeToResult GetRelativeTo(ObjectInstance options)
+{
+    // Clear, self-documenting at call site
+    return new RelativeToResult(plainDate, zonedDateTime);
+}
+
+// Usage is clear and type-safe
+var result = GetRelativeTo(options);
+if (result.PlainRelativeTo != null)
+{
+    // Use result.PlainRelativeTo
+}
+```
+
+**When to use each:**
+- **readonly record struct**: Multiple related return values (2+), especially when used across multiple methods
+- **Class/struct**: Complex data with behavior, validation, or many fields (5+)
+
 ## Testing
 
 - **Jint.Tests/**: Main test suite using xUnit v3

diff --git a/Jint.Tests.Test262/Test262Harness.settings.json b/Jint.Tests.Test262/Test262Harness.settings.json
@@ -1,5 +1,5 @@
 {
-  "SuiteGitSha": "f85c9511a380b9abb2877c42cc47e8fce06d56c5",
+  "SuiteGitSha": "f2d59ea6e4b2f6f87de9f0d18a41d73782b6a9bc",
   //"SuiteDirectory": "//mnt/c/work/test262",
   "TargetPath": "./Generated",
   "Namespace": "Jint.Tests.Test262",
@@ -12,7 +12,8 @@
     "regexp-v-flag",
     "source-phase-imports",
     "tail-call-optimization",
-    "Temporal"
+    "Temporal",
+    "Intl.Era-monthcode"
   ],
   "ExcludedFlags": [
     "CanBlockIsFalse"
@@ -180,7 +181,10 @@
 
     // Misc intl402 tests requiring full locale support
     "intl402/fallback-locales-are-supported.js",
-    "intl402/supportedLocalesOf-consistent-with-resolvedOptions.js"
+    "intl402/supportedLocalesOf-consistent-with-resolvedOptions.js",
 
+    // misc features that require investigation
+    "intl402/NumberFormat/prototype/format/numbering-systems.js",
+    "intl402/Intl/supportedValuesOf/numberingSystems-with-simple-digit-mappings.js"
   ]
 }
diff --git a/Jint.Tests/Parser/JavascriptParserTests.cs b/Jint.Tests/Parser/JavascriptParserTests.cs
@@ -177,6 +177,6 @@ public void ShouldThrowErrorForInvalidLeftHandOperation()
     [InlineData("-.-")]
     public void ShouldThrowParseErrorExceptionForInvalidCode(string code)
     {
-        Assert.Throws<SyntaxErrorException>(() => new Parser().ParseScript(code));
+        Assert.Throws<Acornima.SyntaxErrorException>(() => new Parser().ParseScript(code));
     }
 }
diff --git a/Jint.Tests/Runtime/Debugger/EvaluateTests.cs b/Jint.Tests/Runtime/Debugger/EvaluateTests.cs
@@ -72,7 +72,7 @@ function test(x)
         {
             var exception = Assert.Throws<DebugEvaluationException>(() =>
                 engine.Debugger.Evaluate("this is a syntax error"));
-            Assert.IsType<SyntaxErrorException>(exception.InnerException);
+            Assert.IsType<Acornima.SyntaxErrorException>(exception.InnerException);
         });
     }
 
@@ -111,4 +111,4 @@ function test(x)
             Assert.Equal(frameBefore.Function, frameAfter.Function);
         });
     }
-}
+}
diff --git a/Jint/Extensions/Polyfills.cs b/Jint/Extensions/Polyfills.cs
@@ -1,3 +1,5 @@
+using System.Globalization;
+
 namespace Jint;
 
 internal static class Polyfills
@@ -15,3 +17,77 @@ internal static class Polyfills
     internal static bool Contains(this ReadOnlySpan<string> source, string c) => source.IndexOf(c) != -1;
 #endif
 }
+
+public static class Int32Extensions
+{
+    extension(int)
+    {
+#if NETFRAMEWORK || NETSTANDARD2_0
+        public static bool TryParse(ReadOnlySpan<char> span, NumberStyles style, IFormatProvider provider, out int value)
+        {
+            return int.TryParse(span.ToString(), style, provider, out value);
+        }
+#endif
+
+#if NETFRAMEWORK || NETSTANDARD
+        public static int Parse(ReadOnlySpan<char> span, IFormatProvider? provider = null)
+        {
+            return int.Parse(span.ToString(), NumberStyles.Integer, provider);
+        }
+#endif
+
+#if NETFRAMEWORK || NETSTANDARD2_0
+        public static int Parse(ReadOnlySpan<char> span, NumberStyles style = NumberStyles.Integer, IFormatProvider? provider = null)
+        {
+            return int.Parse(span.ToString(), style, provider);
+        }
+#endif
+    }
+}
+
+public static class Int64Extensions
+{
+    extension(long)
+    {
+#if NETFRAMEWORK || NETSTANDARD2_0
+        public static bool TryParse(ReadOnlySpan<char> span, NumberStyles style, IFormatProvider formatProvider, out long value)
+        {
+            return long.TryParse(span.ToString(), style, formatProvider, out value);
+        }
+#endif
+
+#if NETFRAMEWORK || NETSTANDARD
+        public static long Parse(ReadOnlySpan<char> span, IFormatProvider? provider = null)
+        {
+            return long.Parse(span.ToString(), NumberStyles.Integer, provider);
+        }
+#endif
+
+#if NETFRAMEWORK || NETSTANDARD2_0
+        public static long Parse(ReadOnlySpan<char> span, NumberStyles style = NumberStyles.Integer, IFormatProvider? provider = null)
+        {
+            return long.Parse(span.ToString(), style, provider);
+        }
+#endif
+    }
+}
+
+public static class DoubleExtensions
+{
+    extension(double)
+    {
+#if NETFRAMEWORK || NETSTANDARD
+        public static double Parse(ReadOnlySpan<char> span, IFormatProvider? provider = null)
+        {
+            return double.Parse(span.ToString(), NumberStyles.Float | NumberStyles.AllowThousands, provider);
+        }
+#endif
+
+#if NETFRAMEWORK || NETSTANDARD2_0
+        public static double Parse(ReadOnlySpan<char> span, NumberStyles style = NumberStyles.Float | NumberStyles.AllowThousands, IFormatProvider? provider = null)
+        {
+            return double.Parse(span.ToString(), style, provider);
+        }
+#endif
+    }
+}
diff --git a/Jint/Native/Disposable/DisposeCapability.cs b/Jint/Native/Disposable/DisposeCapability.cs
@@ -89,6 +89,10 @@ public Completion DisposeResources(Completion c)
                         {
                             result = result.UnwrapIfPromise(_engine.Options.Constraints.PromiseTimeout);
                         }
+                        catch (PromiseRejectedException e)
+                        {
+                            exception = new JavaScriptException(e.RejectedValue);
+                        }
                         catch (JavaScriptException e)
                         {
                             exception = e;

diff --git a/Jint/Native/Generator/GeneratorInstance.cs b/Jint/Native/Generator/GeneratorInstance.cs
@@ -237,6 +237,13 @@ private ObjectInstance ResumeExecution(in ExecutionContext genContext, Evaluatio
         var result = _generatorBody.Execute(context);
         _engine.LeaveExecutionContext();
 
+        // https://tc39.es/ecma262/#sec-generatorstart step 4.i-j
+        // Dispose resources when generator body completes (not when yielding)
+        if (_generatorState != GeneratorState.SuspendedYield)
+        {
+            result = genContext.LexicalEnvironment.DisposeResources(result);
+        }
+
         ObjectInstance? resultValue = null;
         if (result.Type == CompletionType.Normal)
         {

diff --git a/Jint/Native/Intl/DateTimeFormatConstructor.cs b/Jint/Native/Intl/DateTimeFormatConstructor.cs
@@ -393,46 +393,6 @@ public override ObjectInstance Construct(JsCallArguments arguments, JsValue newT
         return stringValue;
     }
 
-    private string? GetNumberingSystemOption(ObjectInstance options, List<string> requestedLocales)
-    {
-        var value = options.Get("numberingSystem");
-        string? requestedNS = null;
-
-        if (!value.IsUndefined())
-        {
-            requestedNS = TypeConverter.ToString(value);
-
-            // Validate against pattern
-            if (!IntlUtilities.IsValidUnicodeExtensionValue(requestedNS))
-            {
-                Throw.RangeError(_realm, $"Invalid value '{requestedNS}' for option 'numberingSystem'");
-            }
-        }
-        else if (requestedLocales.Count > 0)
-        {
-            // Check for unicode extension -u-nu-
-            requestedNS = ExtractUnicodeExtensionFromLocale(requestedLocales[0], "nu");
-        }
-
-        // Validate against supported numbering systems
-        // Only return numbering systems we actually support (have digit mappings for)
-        if (requestedNS != null)
-        {
-            var supported = _engine.Options.Intl.CldrProvider.GetSupportedNumberingSystems();
-            foreach (var ns in supported)
-            {
-                if (string.Equals(ns, requestedNS, StringComparison.OrdinalIgnoreCase))
-                {
-                    return ns; // Return canonical form
-                }
-            }
-            // Unsupported numbering system - fall back to null (will use locale default)
-            return null;
-        }
-
-        return null;
-    }
-
     private int? GetNumberOption(ObjectInstance options, string property, int minimum, int maximum, int? fallback)
     {
         var value = options.Get(property);
@@ -665,27 +625,6 @@ private static string BuildResolvedLocale(string baseLocale, string requestedLoc
         };
     }
 
-    /// <summary>
-    /// Extracts a unicode extension value from the locale list.
-    /// For example, extracts "h11" from "de-u-hc-h11" when key is "hc".
-    /// </summary>
-    private static string? ExtractUnicodeExtensionValue(List<string> locales, string key, HashSet<string>? validValues)
-    {
-        foreach (var locale in locales)
-        {
-            var value = ExtractUnicodeExtensionFromLocale(locale, key);
-            if (value != null)
-            {
-                // Validate against allowed values if provided
-                if (validValues == null || validValues.Contains(value))
-                {
-                    return value;
-                }
-            }
-        }
-        return null;
-    }
-
     /// <summary>
     /// Extracts a specific unicode extension value from a single locale string.
     /// </summary>

diff --git a/Jint/Native/Intl/DateTimeFormatPrototype.cs b/Jint/Native/Intl/DateTimeFormatPrototype.cs
@@ -105,53 +105,6 @@ private JsArray FormatToParts(JsValue thisObject, JsCallArguments arguments)
         return result;
     }
 
-    private DateTime ToDateTime(JsValue value)
-    {
-        if (value.IsUndefined())
-        {
-            return DateTime.Now;
-        }
-
-        if (value is JsDate jsDate)
-        {
-            // Check if date is within .NET DateTime range
-            if (!jsDate.DateTimeRangeValid)
-            {
-                // Date is outside .NET range - return min/max based on sign
-                return jsDate.DateValue < 0 ? DateTime.MinValue : DateTime.MaxValue;
-            }
-
-            // ECMA-402 requires formatting in local time unless a specific timezone is provided
-            var dt = jsDate.ToDateTime();
-            if (dt.Kind == DateTimeKind.Utc || dt.Kind == DateTimeKind.Unspecified)
-            {
-                dt = dt.ToLocalTime();
-            }
-            return dt;
-        }
-
-        var timeValue = TypeConverter.ToNumber(value);
-        DatePresentation presentation = timeValue;
-        presentation = presentation.TimeClip();
-
-        if (presentation.IsNaN)
-        {
-            Throw.RangeError(_realm, "Invalid time value");
-        }
-
-        // Clamp to .NET DateTime range if necessary
-        if (presentation.Value < JsDate.Min)
-        {
-            return DateTime.MinValue;
-        }
-        if (presentation.Value > JsDate.Max)
-        {
-            return DateTime.MaxValue;
-        }
-
-        return presentation.ToDateTime().ToLocalTime();
-    }
-
     /// <summary>
     /// Converts a JavaScript value to DateTime, returning the original JavaScript year
     /// when the date is outside .NET DateTime range (for proper era formatting).

diff --git a/Jint/Native/Intl/DurationFormatConstructor.cs b/Jint/Native/Intl/DurationFormatConstructor.cs
@@ -1,5 +1,3 @@
-#pragma warning disable CA1859 // Use concrete types when possible for improved performance -- ClrFunction requires JsValue
-
 using System.Globalization;
 using Jint.Native.Function;
 using Jint.Native.Object;
@@ -280,7 +278,7 @@ private string GetNumberingSystemOption(ObjectInstance options)
     /// <summary>
     /// https://tc39.es/proposal-intl-duration-format/#sec-intl.durationformat.supportedlocalesof
     /// </summary>
-    private JsValue SupportedLocalesOf(JsValue thisObject, JsCallArguments arguments)
+    private JsArray SupportedLocalesOf(JsValue thisObject, JsCallArguments arguments)
     {
         var locales = arguments.At(0);
         var options = arguments.At(1);

diff --git a/Jint/Native/Intl/DurationFormatPrototype.cs b/Jint/Native/Intl/DurationFormatPrototype.cs
@@ -1,5 +1,3 @@
-#pragma warning disable CA1859 // Use concrete types when possible for improved performance -- prototype methods return JsValue
-
 using Jint.Native.Object;
 using Jint.Native.Symbol;
 using Jint.Runtime;
@@ -72,7 +70,7 @@ private JsValue Format(JsValue thisObject, JsCallArguments arguments)
     /// <summary>
     /// https://tc39.es/proposal-intl-duration-format/#sec-intl.durationformat.prototype.formattoparts
     /// </summary>
-    private JsValue FormatToParts(JsValue thisObject, JsCallArguments arguments)
+    private JsArray FormatToParts(JsValue thisObject, JsCallArguments arguments)
     {
         var durationFormat = ValidateDurationFormat(thisObject);
         var duration = arguments.At(0);
@@ -84,7 +82,7 @@ private JsValue FormatToParts(JsValue thisObject, JsCallArguments arguments)
     /// <summary>
     /// https://tc39.es/proposal-intl-duration-format/#sec-intl.durationformat.prototype.resolvedoptions
     /// </summary>
-    private JsValue ResolvedOptions(JsValue thisObject, JsCallArguments arguments)
+    private JsObject ResolvedOptions(JsValue thisObject, JsCallArguments arguments)
     {
         var durationFormat = ValidateDurationFormat(thisObject);