bug: If property doesn't exist on object, don't throw KeyNotFoundExce…

…ption

The spec says to check if the descriptor is undefined when calling
OrdinaryGet. Before this commit, we always tried to get the property
from the internal dictionary.

This would cause internal errors, throwing a KeyNotFoundException if the
property did not exist on the object.

JSS.Lib.UnitTests/ASTTests.cs

@@ -848,6 +848,38 @@ public void ComputedProperties_HaveTheSameValue_AsNormalProperties()
         shouldBeTrue!.Value.Should().BeTrue();
     }
 
+    [Test]
+    public void Properties_ShouldReturnUndefined_WhenReferecingProperty_ThatDoesntExist()
+    {
+        // Arrange
+        var script = ParseScript("let a = {}; a.b");
+
+        // Act
+        var actualCompletion = script.ScriptEvaluation();
+
+        // Assert
+        actualCompletion.IsNormalCompletion().Should().BeTrue();
+
+        var shouldBeTrue = actualCompletion.Value as Undefined;
+        shouldBeTrue.Should().NotBeNull();
+    }
+
+    [Test]
+    public void ComputedProperties_ShouldReturnUndefined_WhenReferecingProperty_ThatDoesntExist()
+    {
+        // Arrange
+        var script = ParseScript("let a = {}; a[\"b\"]");
+
+        // Act
+        var actualCompletion = script.ScriptEvaluation();
+
+        // Assert
+        actualCompletion.IsNormalCompletion().Should().BeTrue();
+
+        var shouldBeTrue = actualCompletion.Value as Undefined;
+        shouldBeTrue.Should().NotBeNull();
+    }
+
     // FIXME: We should have a different file for runtime tests
     [Test]
     public void TypeOf_ObjectConstructor_ReturnsAString_EqualToFunction()

JSS.Lib/AST/Values/Object.cs

@@ -172,11 +172,18 @@ internal Completion Get(string P, Object receiver)
     // 10.1.8.1 OrdinaryGet ( O, P, Receiver ), https://tc39.es/ecma262/#sec-ordinaryget
     static internal Completion OrdinaryGet(Object O, string P, Object receiver)
     {
-        // FIXME: 1. Let desc be ? O.[[GetOwnProperty]](P).
-        // FIXME: 2. If desc is undefined, then
-        // FIXME: a. Let parent be ? O.[[GetPrototypeOf]]().
-        // FIXME: b. If parent is null, return undefined.
-        // FIXME: c. Return ? parent.[[Get]](P, Receiver).
+        // 1. Let desc be ? O.[[GetOwnProperty]](P).
+        var desc = O.GetOwnProperty(P);
+        if (desc.IsAbruptCompletion()) return desc;
+
+        // 2. If desc is undefined, then
+        if (desc.Value.IsUndefined())
+        {
+            // FIXME: a. Let parent be ? O.[[GetPrototypeOf]]().
+            // FIXME: b. If parent is null, return undefined.
+            // FIXME: c. Return ? parent.[[Get]](P, Receiver).
+            return Undefined.The;
+        }
 
         // FIXME: 3. If IsDataDescriptor(desc) is true, return desc.[[Value]].
         return O.DataProperties[P].Value;