Built-in shapes default-on via base class (opt-out); shape Temporal.Now

Jint.Benchmark/BuiltinShapeBenchmark.cs

@@ -58,4 +58,15 @@ public Engine EngineInitBuiltins()
         engine.Evaluate(_initBuiltins);
         return engine;
     }
+
+    // Forces Temporal.Now (9 functions) to initialize — newly shape-backed here, dictionary on main.
+    private static readonly Prepared<Script> _initTemporalNow = Engine.PrepareScript("Temporal.Now.instant();");
+
+    [Benchmark]
+    public Engine EngineInitTemporalNow()
+    {
+        var engine = new Engine();
+        engine.Evaluate(_initTemporalNow);
+        return engine;
+    }
 }

Jint.SourceGenerators/Attributes.cs

@@ -22,13 +22,15 @@ internal sealed class JsObjectAttribute : global::System.Attribute
             public int ExtraCapacity { get; set; }
 
             /// <summary>
-            /// Store this built-in's string-keyed own properties as a shared immutable BuiltinShape plus a
-            /// per-realm lazily-filled descriptor array instead of a per-realm property dictionary. The host
-            /// must derive from <c>BuiltinShapeObject</c>. Supported for hosts whose members are
-            /// [JsFunction]s, static-immutable [JsProperty] constants, and [JsSymbol]s (namespace built-ins
-            /// such as Math/JSON/Reflect/Atomics). See BuiltinShapeObject.
+            /// Built-in shape storage (a shared immutable BuiltinShape plus a per-realm lazily-filled
+            /// descriptor array instead of a per-realm property dictionary) is used <b>by default</b> for any
+            /// host that derives from <c>BuiltinShapeObject</c> — deriving from it is the opt-in. Set this to
+            /// <c>false</c> to opt a derived host back out to the dictionary path. Hosts that do not derive
+            /// from <c>BuiltinShapeObject</c> always use the dictionary path regardless of this flag.
+            /// Supported members: [JsFunction]s, static-immutable [JsProperty] constants, and symbols. See
+            /// BuiltinShapeObject.
             /// </summary>
-            public bool UseShape { get; set; }
+            public bool UseShape { get; set; } = true;
         }
 
         [global::System.AttributeUsage(global::System.AttributeTargets.Method)]

Jint.SourceGenerators/Diagnostics.cs

@@ -107,4 +107,12 @@ internal static class DiagnosticDescriptors
         category: "Jint.SourceGenerators",
         defaultSeverity: DiagnosticSeverity.Error,
         isEnabledByDefault: true);
+
+    public static readonly DiagnosticDescriptor UnsupportedShapeMember = new(
+        id: "JINT022",
+        title: "Built-in shape host has an unsupported member kind",
+        messageFormat: "Type '{0}' uses built-in shape storage (derives from BuiltinShapeObject) but declares an accessor / intrinsic reference / thrower / non-static or mutable property, which the shape path does not support; add [JsObject(UseShape = false)] or remove the member",
+        category: "Jint.SourceGenerators",
+        defaultSeverity: DiagnosticSeverity.Error,
+        isEnabledByDefault: true);
 }

Jint.SourceGenerators/Models.cs

@@ -98,19 +98,32 @@ public IEnumerable<Diagnostic> Diagnostics
             ? string.Empty
             : typeSymbol.ContainingNamespace.ToDisplayString();
 
-        // Read [JsObject(ExtraCapacity = N, UseShape = true)].
+        // Read [JsObject(ExtraCapacity = N, UseShape = ...)]. Shape storage is the default for any host
+        // that derives from BuiltinShapeObject (deriving from it is the opt-in); UseShape = false is the
+        // explicit opt-out. Hosts that don't derive from it always use the dictionary path regardless.
         var extraCapacity = 0;
-        var useShape = false;
+        var useShapeRequested = true;
         foreach (var attr in typeSymbol.GetAttributes())
         {
             if (attr.AttributeClass?.Name != "JsObjectAttribute") continue;
             foreach (var named in attr.NamedArguments)
             {
                 if (named.Key == "ExtraCapacity" && named.Value.Value is int v) extraCapacity = v;
-                else if (named.Key == "UseShape" && named.Value.Value is bool s) useShape = s;
+                else if (named.Key == "UseShape" && named.Value.Value is bool s) useShapeRequested = s;
             }
         }
 
+        var derivesFromBuiltinShapeObject = false;
+        for (var baseType = typeSymbol.BaseType; baseType is not null; baseType = baseType.BaseType)
+        {
+            if (baseType.Name == "BuiltinShapeObject")
+            {
+                derivesFromBuiltinShapeObject = true;
+                break;
+            }
+        }
+        var useShape = useShapeRequested && derivesFromBuiltinShapeObject;
+
         var functions = new List<FunctionDefinition>();
         var properties = new List<PropertyDefinition>();
         var symbols = new List<SymbolDefinition>();
@@ -329,6 +342,31 @@ public IEnumerable<Diagnostic> Diagnostics
                 typeSymbol.Name));
         }
 
+        // The shape path supports [JsFunction]s, static-immutable [JsProperty] constants, and symbols
+        // (incl. symbol-keyed functions). Accessors, intrinsic references, throwers and instance/mutable
+        // properties aren't representable — fail loudly rather than silently dropping them.
+        if (useShape)
+        {
+            var hasUnsupported = intrinsicReferences.Count > 0 || throwerAccessors.Count > 0;
+            foreach (var fn in functions)
+            {
+                if (fn.Registration is RegistrationKind.AccessorGet or RegistrationKind.AccessorSet
+                    or RegistrationKind.SymbolAccessorGet or RegistrationKind.SymbolAccessorSet)
+                {
+                    hasUnsupported = true;
+                    break;
+                }
+            }
+            foreach (var p in properties)
+            {
+                if (!p.IsStatic || !p.IsImmutable) { hasUnsupported = true; break; }
+            }
+            if (hasUnsupported)
+            {
+                diagnostics.Add(new DiagnosticInfo(DiagnosticDescriptors.UnsupportedShapeMember, location, typeSymbol.Name));
+            }
+        }
+
         functions.Sort(static (a, b) => string.CompareOrdinal(a.JsName, b.JsName));
         properties.Sort(static (a, b) => string.CompareOrdinal(a.JsName, b.JsName));
         symbols.Sort(static (a, b) => string.CompareOrdinal(a.SymbolName, b.SymbolName));

Jint.Tests.SourceGenerators/Snapshots/ObjectGeneratorTests.AccessorGetterAndSetter#JintAttributes.g.verified.cs

@@ -18,13 +18,15 @@ internal sealed class JsObjectAttribute : global::System.Attribute
     public int ExtraCapacity { get; set; }
 
     /// <summary>
-    /// Store this built-in's string-keyed own properties as a shared immutable BuiltinShape plus a
-    /// per-realm lazily-filled descriptor array instead of a per-realm property dictionary. The host
-    /// must derive from <c>BuiltinShapeObject</c>. Supported for hosts whose members are
-    /// [JsFunction]s, static-immutable [JsProperty] constants, and [JsSymbol]s (namespace built-ins
-    /// such as Math/JSON/Reflect/Atomics). See BuiltinShapeObject.
+    /// Built-in shape storage (a shared immutable BuiltinShape plus a per-realm lazily-filled
+    /// descriptor array instead of a per-realm property dictionary) is used <b>by default</b> for any
+    /// host that derives from <c>BuiltinShapeObject</c> — deriving from it is the opt-in. Set this to
+    /// <c>false</c> to opt a derived host back out to the dictionary path. Hosts that do not derive
+    /// from <c>BuiltinShapeObject</c> always use the dictionary path regardless of this flag.
+    /// Supported members: [JsFunction]s, static-immutable [JsProperty] constants, and symbols. See
+    /// BuiltinShapeObject.
     /// </summary>
-    public bool UseShape { get; set; }
+    public bool UseShape { get; set; } = true;
 }
 
 [global::System.AttributeUsage(global::System.AttributeTargets.Method)]

Jint.Tests.SourceGenerators/Snapshots/ObjectGeneratorTests.AccessorGetterOnly#JintAttributes.g.verified.cs

@@ -18,13 +18,15 @@ internal sealed class JsObjectAttribute : global::System.Attribute
     public int ExtraCapacity { get; set; }
 
     /// <summary>
-    /// Store this built-in's string-keyed own properties as a shared immutable BuiltinShape plus a
-    /// per-realm lazily-filled descriptor array instead of a per-realm property dictionary. The host
-    /// must derive from <c>BuiltinShapeObject</c>. Supported for hosts whose members are
-    /// [JsFunction]s, static-immutable [JsProperty] constants, and [JsSymbol]s (namespace built-ins
-    /// such as Math/JSON/Reflect/Atomics). See BuiltinShapeObject.
+    /// Built-in shape storage (a shared immutable BuiltinShape plus a per-realm lazily-filled
+    /// descriptor array instead of a per-realm property dictionary) is used <b>by default</b> for any
+    /// host that derives from <c>BuiltinShapeObject</c> — deriving from it is the opt-in. Set this to
+    /// <c>false</c> to opt a derived host back out to the dictionary path. Hosts that do not derive
+    /// from <c>BuiltinShapeObject</c> always use the dictionary path regardless of this flag.
+    /// Supported members: [JsFunction]s, static-immutable [JsProperty] constants, and symbols. See
+    /// BuiltinShapeObject.
     /// </summary>
-    public bool UseShape { get; set; }
+    public bool UseShape { get; set; } = true;
 }
 
 [global::System.AttributeUsage(global::System.AttributeTargets.Method)]

Jint.Tests.SourceGenerators/Snapshots/ObjectGeneratorTests.AccessorWrongArity_ProducesDiagnostic#JintAttributes.g.verified.cs

@@ -18,13 +18,15 @@ internal sealed class JsObjectAttribute : global::System.Attribute
     public int ExtraCapacity { get; set; }
 
     /// <summary>
-    /// Store this built-in's string-keyed own properties as a shared immutable BuiltinShape plus a
-    /// per-realm lazily-filled descriptor array instead of a per-realm property dictionary. The host
-    /// must derive from <c>BuiltinShapeObject</c>. Supported for hosts whose members are
-    /// [JsFunction]s, static-immutable [JsProperty] constants, and [JsSymbol]s (namespace built-ins
-    /// such as Math/JSON/Reflect/Atomics). See BuiltinShapeObject.
+    /// Built-in shape storage (a shared immutable BuiltinShape plus a per-realm lazily-filled
+    /// descriptor array instead of a per-realm property dictionary) is used <b>by default</b> for any
+    /// host that derives from <c>BuiltinShapeObject</c> — deriving from it is the opt-in. Set this to
+    /// <c>false</c> to opt a derived host back out to the dictionary path. Hosts that do not derive
+    /// from <c>BuiltinShapeObject</c> always use the dictionary path regardless of this flag.
+    /// Supported members: [JsFunction]s, static-immutable [JsProperty] constants, and symbols. See
+    /// BuiltinShapeObject.
     /// </summary>
-    public bool UseShape { get; set; }
+    public bool UseShape { get; set; } = true;
 }
 
 [global::System.AttributeUsage(global::System.AttributeTargets.Method)]

Jint.Tests.SourceGenerators/Snapshots/ObjectGeneratorTests.CoercedRestSpan#JintAttributes.g.verified.cs

@@ -18,13 +18,15 @@ internal sealed class JsObjectAttribute : global::System.Attribute
     public int ExtraCapacity { get; set; }
 
     /// <summary>
-    /// Store this built-in's string-keyed own properties as a shared immutable BuiltinShape plus a
-    /// per-realm lazily-filled descriptor array instead of a per-realm property dictionary. The host
-    /// must derive from <c>BuiltinShapeObject</c>. Supported for hosts whose members are
-    /// [JsFunction]s, static-immutable [JsProperty] constants, and [JsSymbol]s (namespace built-ins
-    /// such as Math/JSON/Reflect/Atomics). See BuiltinShapeObject.
+    /// Built-in shape storage (a shared immutable BuiltinShape plus a per-realm lazily-filled
+    /// descriptor array instead of a per-realm property dictionary) is used <b>by default</b> for any
+    /// host that derives from <c>BuiltinShapeObject</c> — deriving from it is the opt-in. Set this to
+    /// <c>false</c> to opt a derived host back out to the dictionary path. Hosts that do not derive
+    /// from <c>BuiltinShapeObject</c> always use the dictionary path regardless of this flag.
+    /// Supported members: [JsFunction]s, static-immutable [JsProperty] constants, and symbols. See
+    /// BuiltinShapeObject.
     /// </summary>
-    public bool UseShape { get; set; }
+    public bool UseShape { get; set; } = true;
 }
 
 [global::System.AttributeUsage(global::System.AttributeTargets.Method)]

Jint.Tests.SourceGenerators/Snapshots/ObjectGeneratorTests.CoercedRestSpanTypeMismatch_ProducesDiagnostic#JintAttributes.g.verified.cs

@@ -18,13 +18,15 @@ internal sealed class JsObjectAttribute : global::System.Attribute
     public int ExtraCapacity { get; set; }
 
     /// <summary>
-    /// Store this built-in's string-keyed own properties as a shared immutable BuiltinShape plus a
-    /// per-realm lazily-filled descriptor array instead of a per-realm property dictionary. The host
-    /// must derive from <c>BuiltinShapeObject</c>. Supported for hosts whose members are
-    /// [JsFunction]s, static-immutable [JsProperty] constants, and [JsSymbol]s (namespace built-ins
-    /// such as Math/JSON/Reflect/Atomics). See BuiltinShapeObject.
+    /// Built-in shape storage (a shared immutable BuiltinShape plus a per-realm lazily-filled
+    /// descriptor array instead of a per-realm property dictionary) is used <b>by default</b> for any
+    /// host that derives from <c>BuiltinShapeObject</c> — deriving from it is the opt-in. Set this to
+    /// <c>false</c> to opt a derived host back out to the dictionary path. Hosts that do not derive
+    /// from <c>BuiltinShapeObject</c> always use the dictionary path regardless of this flag.
+    /// Supported members: [JsFunction]s, static-immutable [JsProperty] constants, and symbols. See
+    /// BuiltinShapeObject.
     /// </summary>
-    public bool UseShape { get; set; }
+    public bool UseShape { get; set; } = true;
 }
 
 [global::System.AttributeUsage(global::System.AttributeTargets.Method)]

Jint.Tests.SourceGenerators/Snapshots/ObjectGeneratorTests.ConflictingAccessorFlags_ProducesDiagnostic#JintAttributes.g.verified.cs

@@ -18,13 +18,15 @@ internal sealed class JsObjectAttribute : global::System.Attribute
     public int ExtraCapacity { get; set; }
 
     /// <summary>
-    /// Store this built-in's string-keyed own properties as a shared immutable BuiltinShape plus a
-    /// per-realm lazily-filled descriptor array instead of a per-realm property dictionary. The host
-    /// must derive from <c>BuiltinShapeObject</c>. Supported for hosts whose members are
-    /// [JsFunction]s, static-immutable [JsProperty] constants, and [JsSymbol]s (namespace built-ins
-    /// such as Math/JSON/Reflect/Atomics). See BuiltinShapeObject.
+    /// Built-in shape storage (a shared immutable BuiltinShape plus a per-realm lazily-filled
+    /// descriptor array instead of a per-realm property dictionary) is used <b>by default</b> for any
+    /// host that derives from <c>BuiltinShapeObject</c> — deriving from it is the opt-in. Set this to
+    /// <c>false</c> to opt a derived host back out to the dictionary path. Hosts that do not derive
+    /// from <c>BuiltinShapeObject</c> always use the dictionary path regardless of this flag.
+    /// Supported members: [JsFunction]s, static-immutable [JsProperty] constants, and symbols. See
+    /// BuiltinShapeObject.
     /// </summary>
-    public bool UseShape { get; set; }
+    public bool UseShape { get; set; } = true;
 }
 
 [global::System.AttributeUsage(global::System.AttributeTargets.Method)]

Jint.Tests.SourceGenerators/Snapshots/ObjectGeneratorTests.ConflictingConversionAttrs_ProducesDiagnostic#JintAttributes.g.verified.cs

@@ -18,13 +18,15 @@ internal sealed class JsObjectAttribute : global::System.Attribute
     public int ExtraCapacity { get; set; }
 
     /// <summary>
-    /// Store this built-in's string-keyed own properties as a shared immutable BuiltinShape plus a
-    /// per-realm lazily-filled descriptor array instead of a per-realm property dictionary. The host
-    /// must derive from <c>BuiltinShapeObject</c>. Supported for hosts whose members are
-    /// [JsFunction]s, static-immutable [JsProperty] constants, and [JsSymbol]s (namespace built-ins
-    /// such as Math/JSON/Reflect/Atomics). See BuiltinShapeObject.
+    /// Built-in shape storage (a shared immutable BuiltinShape plus a per-realm lazily-filled
+    /// descriptor array instead of a per-realm property dictionary) is used <b>by default</b> for any
+    /// host that derives from <c>BuiltinShapeObject</c> — deriving from it is the opt-in. Set this to
+    /// <c>false</c> to opt a derived host back out to the dictionary path. Hosts that do not derive
+    /// from <c>BuiltinShapeObject</c> always use the dictionary path regardless of this flag.
+    /// Supported members: [JsFunction]s, static-immutable [JsProperty] constants, and symbols. See
+    /// BuiltinShapeObject.
     /// </summary>
-    public bool UseShape { get; set; }
+    public bool UseShape { get; set; } = true;
 }
 
 [global::System.AttributeUsage(global::System.AttributeTargets.Method)]

Jint.Tests.SourceGenerators/Snapshots/ObjectGeneratorTests.ConversionTypeMismatch_ProducesDiagnostic#JintAttributes.g.verified.cs

@@ -18,13 +18,15 @@ internal sealed class JsObjectAttribute : global::System.Attribute
     public int ExtraCapacity { get; set; }
 
     /// <summary>
-    /// Store this built-in's string-keyed own properties as a shared immutable BuiltinShape plus a
-    /// per-realm lazily-filled descriptor array instead of a per-realm property dictionary. The host
-    /// must derive from <c>BuiltinShapeObject</c>. Supported for hosts whose members are
-    /// [JsFunction]s, static-immutable [JsProperty] constants, and [JsSymbol]s (namespace built-ins
-    /// such as Math/JSON/Reflect/Atomics). See BuiltinShapeObject.
+    /// Built-in shape storage (a shared immutable BuiltinShape plus a per-realm lazily-filled
+    /// descriptor array instead of a per-realm property dictionary) is used <b>by default</b> for any
+    /// host that derives from <c>BuiltinShapeObject</c> — deriving from it is the opt-in. Set this to
+    /// <c>false</c> to opt a derived host back out to the dictionary path. Hosts that do not derive
+    /// from <c>BuiltinShapeObject</c> always use the dictionary path regardless of this flag.
+    /// Supported members: [JsFunction]s, static-immutable [JsProperty] constants, and symbols. See
+    /// BuiltinShapeObject.
     /// </summary>
-    public bool UseShape { get; set; }
+    public bool UseShape { get; set; } = true;
 }
 
 [global::System.AttributeUsage(global::System.AttributeTargets.Method)]

Jint.Tests.SourceGenerators/Snapshots/ObjectGeneratorTests.DuplicateIntrinsicReference_ProducesDiagnostic#JintAttributes.g.verified.cs

@@ -18,13 +18,15 @@ internal sealed class JsObjectAttribute : global::System.Attribute
     public int ExtraCapacity { get; set; }
 
     /// <summary>
-    /// Store this built-in's string-keyed own properties as a shared immutable BuiltinShape plus a
-    /// per-realm lazily-filled descriptor array instead of a per-realm property dictionary. The host
-    /// must derive from <c>BuiltinShapeObject</c>. Supported for hosts whose members are
-    /// [JsFunction]s, static-immutable [JsProperty] constants, and [JsSymbol]s (namespace built-ins
-    /// such as Math/JSON/Reflect/Atomics). See BuiltinShapeObject.
+    /// Built-in shape storage (a shared immutable BuiltinShape plus a per-realm lazily-filled
+    /// descriptor array instead of a per-realm property dictionary) is used <b>by default</b> for any
+    /// host that derives from <c>BuiltinShapeObject</c> — deriving from it is the opt-in. Set this to
+    /// <c>false</c> to opt a derived host back out to the dictionary path. Hosts that do not derive
+    /// from <c>BuiltinShapeObject</c> always use the dictionary path regardless of this flag.
+    /// Supported members: [JsFunction]s, static-immutable [JsProperty] constants, and symbols. See
+    /// BuiltinShapeObject.
     /// </summary>
-    public bool UseShape { get; set; }
+    public bool UseShape { get; set; } = true;
 }
 
 [global::System.AttributeUsage(global::System.AttributeTargets.Method)]