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Merged
lahma merged 1 commit into from
Jul 13, 2026
Merged

Give every Proxy invariant violation a descriptive TypeError message #2677

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23 changes: 23 additions & 0 deletions Jint.Tests/Runtime/ProxyTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -92,6 +92,29 @@ public void ConstructTrapAcceptsSingleFractionalArgument()
Assert.Equal(1.5, result.AsNumber());
}

[Fact]
public void ProxyInvariantViolationsHaveDescriptiveMessages()
{
_engine.Execute("""
var frozen = Object.freeze({ a: 1 });
var pHas = new Proxy(frozen, { has: () => false });
var pOwnKeys = new Proxy(frozen, { ownKeys: () => ['b'] });
var pPrevent = new Proxy({}, { preventExtensions: () => true });
""");

var ex = Assert.Throws<JavaScriptException>(() => _engine.Evaluate("'a' in pHas"));
AssertJsTypeError(_engine, ex, "'has' on proxy: trap returned falsish for property 'a' which exists in the proxy target as non-configurable");

ex = Assert.Throws<JavaScriptException>(() => _engine.Evaluate("Object.keys(pOwnKeys)"));
AssertJsTypeError(_engine, ex, "'ownKeys' on proxy: trap result did not include non-configurable property 'a' of the proxy target");

ex = Assert.Throws<JavaScriptException>(() => _engine.Evaluate("Object.preventExtensions(pPrevent)"));
AssertJsTypeError(_engine, ex, "'preventExtensions' on proxy: trap returned truish but the proxy target is extensible");

ex = Assert.Throws<JavaScriptException>(() => _engine.Evaluate("new Proxy({}, { get: 1 }).x"));
AssertJsTypeError(_engine, ex, "'get' trap of proxy handler is not a function");
}

[Fact]
public void ProxyToStringUseTarget()
{
Expand Down
59 changes: 34 additions & 25 deletions Jint/Native/JsProxy.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -97,7 +97,7 @@ ObjectInstance IConstructor.Construct(JsCallArguments arguments, JsValue newTarg
var constructor = target as IConstructor;
if (constructor is null)
{
Throw.TypeError(_engine.Realm);
Throw.TypeError(_engine.Realm, "Proxy target is not a constructor");
}

return constructor.Construct(arguments, newTarget);
Expand All @@ -111,7 +111,7 @@ ObjectInstance IConstructor.Construct(JsCallArguments arguments, JsValue newTarg
var oi = result as ObjectInstance;
if (oi is null)
{
Throw.TypeError(_engine.Realm);
Throw.TypeError(_engine.Realm, $"'construct' on proxy: trap returned non-object ('{result}')");
}

return oi;
Expand Down Expand Up @@ -195,7 +195,7 @@ private List<JsValue> ValidateOwnKeysTrapResult(ObjectInstance target, JsValue r
{
if (!uncheckedResultKeys.Add(key))
{
Throw.TypeError(_engine.Realm);
Throw.TypeError(_engine.Realm, $"'ownKeys' on proxy: trap returned duplicate entries ('{key}')");
}
trapResult.Add(key);
}
Expand Down Expand Up @@ -228,7 +228,7 @@ private List<JsValue> ValidateOwnKeysTrapResult(ObjectInstance target, JsValue r
var key = targetNonconfigurableKeys[i];
if (!uncheckedResultKeys.Remove(key))
{
Throw.TypeError(_engine.Realm);
Throw.TypeError(_engine.Realm, $"'ownKeys' on proxy: trap result did not include non-configurable property '{key}' of the proxy target");
}
}
}
Expand All @@ -245,14 +245,14 @@ private List<JsValue> ValidateOwnKeysTrapResult(ObjectInstance target, JsValue r
var key = targetConfigurableKeys[i];
if (!uncheckedResultKeys.Remove(key))
{
Throw.TypeError(_engine.Realm);
Throw.TypeError(_engine.Realm, $"'ownKeys' on proxy: trap result did not include property '{key}' of the non-extensible proxy target");
}
}
}

if (uncheckedResultKeys.Count > 0)
{
Throw.TypeError(_engine.Realm);
Throw.TypeError(_engine.Realm, "'ownKeys' on proxy: trap returned extra keys but proxy target is non-extensible");
}

return trapResult;
Expand All @@ -278,7 +278,7 @@ private PropertyDescriptor ValidateGetOwnPropertyTrapResult(ObjectInstance targe
{
if (!trapResultObj.IsObject() && !trapResultObj.IsUndefined())
{
Throw.TypeError(_engine.Realm);
Throw.TypeError(_engine.Realm, $"'getOwnPropertyDescriptor' on proxy: trap returned neither object nor undefined for property '{property}'");
}

var targetDesc = target.GetOwnProperty(property);
Expand All @@ -290,9 +290,14 @@ private PropertyDescriptor ValidateGetOwnPropertyTrapResult(ObjectInstance targe
return targetDesc;
}

if (!targetDesc.Configurable || !target.Extensible)
if (!targetDesc.Configurable)
{
Throw.TypeError(_engine.Realm);
Throw.TypeError(_engine.Realm, $"'getOwnPropertyDescriptor' on proxy: trap returned undefined for property '{property}' which is non-configurable in the proxy target");
}

if (!target.Extensible)
{
Throw.TypeError(_engine.Realm, $"'getOwnPropertyDescriptor' on proxy: trap returned undefined for property '{property}' which exists in the non-extensible proxy target");
}

return PropertyDescriptor.Undefined;
Expand All @@ -305,21 +310,21 @@ private PropertyDescriptor ValidateGetOwnPropertyTrapResult(ObjectInstance targe
var valid = IsCompatiblePropertyDescriptor(extensibleTarget, resultDesc, targetDesc);
if (!valid)
{
Throw.TypeError(_engine.Realm);
Throw.TypeError(_engine.Realm, $"'getOwnPropertyDescriptor' on proxy: trap returned descriptor for property '{property}' that is incompatible with the existing property in the proxy target");
}

if (!resultDesc.Configurable)
{
if (targetDesc == PropertyDescriptor.Undefined || targetDesc.Configurable)
{
Throw.TypeError(_engine.Realm);
Throw.TypeError(_engine.Realm, $"'getOwnPropertyDescriptor' on proxy: trap reported non-configurability for property '{property}' which is either non-existent or configurable in the proxy target");
}

if (resultDesc.WritableSet && !resultDesc.Writable)
{
if (targetDesc.Writable)
{
Throw.TypeError(_engine.Realm);
Throw.TypeError(_engine.Realm, $"'getOwnPropertyDescriptor' on proxy: trap reported non-configurable and writable: false for property '{property}' which is non-configurable and writable in the proxy target");
}
}
}
Expand Down Expand Up @@ -434,27 +439,31 @@ private void ValidateDefinePropertyTrapResult(ObjectInstance target, JsValue pro

if (targetDesc == PropertyDescriptor.Undefined)
{
if (!extensibleTarget || settingConfigFalse)
if (!extensibleTarget)
{
Throw.TypeError(_engine.Realm, $"'defineProperty' on proxy: trap returned truish for adding property '{property}' to the non-extensible proxy target");
}
if (settingConfigFalse)
{
Throw.TypeError(_engine.Realm);
Throw.TypeError(_engine.Realm, $"'defineProperty' on proxy: trap returned truish for defining non-configurable property '{property}' which is non-existent in the proxy target");
}
}
else
{
if (!IsCompatiblePropertyDescriptor(extensibleTarget, desc, targetDesc))
{
Throw.TypeError(_engine.Realm);
Throw.TypeError(_engine.Realm, $"'defineProperty' on proxy: trap returned truish for adding property '{property}' that is incompatible with the existing property in the proxy target");
}
if (targetDesc.Configurable && settingConfigFalse)
{
Throw.TypeError(_engine.Realm);
Throw.TypeError(_engine.Realm, $"'defineProperty' on proxy: trap returned truish for defining non-configurable property '{property}' which is configurable in the proxy target");
}

if (targetDesc.IsDataDescriptor() && !targetDesc.Configurable && targetDesc.Writable)
{
if (desc.WritableSet && !desc.Writable)
{
Throw.TypeError(_engine.Realm);
Throw.TypeError(_engine.Realm, $"'defineProperty' on proxy: trap returned truish for defining non-writable property '{property}' which is writable in the proxy target");
}
}
}
Expand Down Expand Up @@ -493,12 +502,12 @@ private void ValidateHasTrapResult(ObjectInstance target, JsValue property)
{
if (!targetDesc.Configurable)
{
Throw.TypeError(_engine.Realm);
Throw.TypeError(_engine.Realm, $"'has' on proxy: trap returned falsish for property '{property}' which exists in the proxy target as non-configurable");
}

if (!target.Extensible)
{
Throw.TypeError(_engine.Realm);
Throw.TypeError(_engine.Realm, $"'has' on proxy: trap returned falsish for property '{property}' but the proxy target is not extensible");
}
}
}
Expand Down Expand Up @@ -540,7 +549,7 @@ private void ValidateDeleteTrapResult(ObjectInstance target, JsValue property)

if (!target.Extensible)
{
Throw.TypeError(_engine.Realm);
Throw.TypeError(_engine.Realm, $"'deleteProperty' on proxy: trap returned truish for property '{property}' but the proxy target is non-extensible");
}
}

Expand All @@ -559,7 +568,7 @@ public override bool PreventExtensions()
var success = TypeConverter.ToBoolean(CallTrap(trap, target));
if (success && target.Extensible)
{
Throw.TypeError(_engine.Realm);
Throw.TypeError(_engine.Realm, "'preventExtensions' on proxy: trap returned truish but the proxy target is extensible");
}

return success;
Expand All @@ -583,7 +592,7 @@ public override bool Extensible
var targetResult = target.Extensible;
if (booleanTrapResult != targetResult)
{
Throw.TypeError(_engine.Realm);
Throw.TypeError(_engine.Realm, $"'isExtensible' on proxy: trap result does not reflect extensibility of proxy target (which is '{(targetResult ? "true" : "false")}')");
}

return booleanTrapResult;
Expand Down Expand Up @@ -617,7 +626,7 @@ public override bool Extensible

if (!ReferenceEquals(proto, target.Prototype))
{
Throw.TypeError(_engine.Realm);
Throw.TypeError(_engine.Realm, "'getPrototypeOf' on proxy: proxy target is non-extensible but the trap did not return its actual prototype");
}

return proto;
Expand Down Expand Up @@ -650,7 +659,7 @@ internal override bool SetPrototypeOf(JsValue value)
var proto = value.IsNull() ? null : value as ObjectInstance;
if (!ReferenceEquals(proto, target.Prototype))
{
Throw.TypeError(_engine.Realm);
Throw.TypeError(_engine.Realm, "'setPrototypeOf' on proxy: trap returned truish for setting a new prototype on the non-extensible proxy target");
}

return true;
Expand Down Expand Up @@ -678,7 +687,7 @@ internal override bool SetPrototypeOf(JsValue value)
var callable = handlerFunction as ICallable;
if (callable is null)
{
Throw.TypeError(_engine.Realm, $"{_handler} returned for property '{trapName}' of object '{_target}' is not a function");
Throw.TypeError(_engine.Realm, $"'{trapName}' trap of proxy handler is not a function");
}

return callable;
Expand Down
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