Debugger improvements 3

Jint.Tests/Runtime/Debugger/DebugHandlerTests.cs

@@ -0,0 +1,52 @@
+using Jint.Native.Object;
+using Jint.Runtime.Debugger;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Xunit;
+
+namespace Jint.Tests.Runtime.Debugger
+{
+    public class DebugHandlerTests
+    {
+        [Fact]
+        public void AvoidsPauseRecursion()
+        {
+            // While the DebugHandler is in a paused state, it shouldn't relay further OnStep calls to Break/Step.
+            // Such calls would occur e.g. if Step/Break event handlers evaluate accessors. Failing to avoid
+            // reentrance in a multithreaded environment (e.g. using ManualResetEvent(Slim)) would cause
+            // a deadlock.
+            string script = @"
+                const obj = { get name() { 'fail'; return 'Smith'; } };
+                'target';
+            ";
+
+            var engine = new Engine(options => options.DebugMode());
+
+            bool didPropertyAccess = false;
+
+            engine.Step += (sender, info) =>
+            {
+                // We should never reach "fail", because the only way it's executed is from
+                // within this Step handler
+                Assert.False(info.ReachedLiteral("fail"));
+
+                if (info.ReachedLiteral("target"))
+                {
+                    var obj = info.CurrentScopeChain.Global["obj"] as ObjectInstance;
+                    var prop = obj.GetOwnProperty("name");
+                    // This is where reentrance would occur:
+                    var value = prop.Get.Invoke();
+                    didPropertyAccess = true;
+                }
+                return StepMode.Into;
+            };
+
+            engine.Execute(script);
+
+            Assert.True(didPropertyAccess);
+        }
+    }
+}