Fix RegExp literal NullReferenceException in getters parsed via ParseExpression

Jint.Tests/Runtime/RegExpTests.cs

@@ -1,5 +1,10 @@
 using System.Text.RegularExpressions;
+using Acornima;
+using Acornima.Ast;
 using Jint.Native;
+using Jint.Native.Function;
+using Jint.Native.Object;
+using Jint.Runtime.Descriptors;
 
 namespace Jint.Tests.Runtime;
 
@@ -139,4 +144,50 @@ public void Issue506()
         var result = engine.Evaluate("/[^]?(:[rp][el]a[\\w-]+)[^]/.test(':reagent-')").AsBoolean();
         Assert.True(result);
     }
+
+    [Fact]
+    public void RegExpLiteralInGetterShouldWork()
+    {
+        // Reproduces issue where using RegExp literal notation in getters parsed via Parser().ParseExpression()
+        // resulted in NullReferenceException due to uncompiled regex
+        var engine = new Engine();
+        var obj = new JsObject(engine);
+
+        // This should not throw NullReferenceException
+        var getterFunction = (IFunction)new Parser().ParseExpression(
+            "function() { return 'test'.match(/[a-z]/)?.[0]; }"
+        );
+        var getter = new ScriptFunction(engine, getterFunction, true);
+
+        obj.FastSetProperty("name", new GetSetPropertyDescriptor(getter, null, true, false));
+        engine.SetValue("customObj", obj);
+
+        engine.Execute(string.Empty);
+        var result = engine.GetValue("customObj").AsObject();
+        var name = result.Get("name").ToString();
+
+        Assert.Equal("t", name);
+    }
+
+    [Fact]
+    public void RegExpLiteralInGetterWorksWithConstructorToo()
+    {
+        // Ensure the alternative RegExp constructor approach continues to work
+        var engine = new Engine();
+        var obj = new JsObject(engine);
+
+        var getterFunction = (IFunction)new Parser().ParseExpression(
+            "function() { return 'test'.match(new RegExp('[a-z]'))?.[0]; }"
+        );
+        var getter = new ScriptFunction(engine, getterFunction, true);
+
+        obj.FastSetProperty("name", new GetSetPropertyDescriptor(getter, null, true, false));
+        engine.SetValue("customObj", obj);
+
+        engine.Execute(string.Empty);
+        var result = engine.GetValue("customObj").AsObject();
+        var name = result.Get("name").ToString();
+
+        Assert.Equal("t", name);
+    }
 }

Jint/Runtime/Interpreter/Expressions/JintLiteralExpression.cs

@@ -68,7 +68,28 @@
             var regExpParseResult = regExpLiteral.ParseResult;
             if (regExpParseResult.Success)
             {
-                var regex = regExpLiteral.UserData as Regex ?? regExpParseResult.Regex!;
+                var regex = regExpLiteral.UserData as Regex ?? regExpParseResult.Regex;
+                if (regex is null)
+                {
+                    // Regex was not compiled during parsing, compile it now
+                    var parserOptions = context.Engine.GetActiveParserOptions();
+                    var compiledResult = Tokenizer.AdaptRegExp(
+                        regExpLiteral.RegExp.Pattern, 
+                        regExpLiteral.RegExp.Flags, 
+                        compiled: false, 
+                        parserOptions.RegexTimeout,
+                        ecmaVersion: parserOptions.EcmaVersion,
+                        experimentalESFeatures: parserOptions.ExperimentalESFeatures);
+
+                    if (!compiledResult.Success)
+                    {
+                        Throw.SyntaxError(context.Engine.Realm, $"Unsupported regular expression. {compiledResult.ConversionError!.Description}");
+                    }
+
+                    regex = compiledResult.Regex!;
+                    regExpParseResult = compiledResult;
+                }
+
                 return context.Engine.Realm.Intrinsics.RegExp.Construct(regex, regExpLiteral.RegExp.Pattern, regExpLiteral.RegExp.Flags, regExpParseResult);
             }