[MERGE #5451 @paolosevMSFT] Ensure that GeneratorReturnExceptions are not handled by InterpreterStackFrame::DebugProcess

Merge pull request #5451 from paolosevMSFT:user/paolosev/bug17418795

When running a generator function with the -debuglaunch flag the engine crashes with simple code like:
```
  function* test() {
    try {
      yield 42;
    } catch (e) {
    }
  }
  var t = test();
  t.next();
  var v = t.return();
```

The reason is that a special exception is thrown by JavascriptOperators::OP_ResumeYield() to carry the return value from a generator. When the generator has a try/catch, like in this case, this exception is caught and rethrown by InterpreterStackFrame::OP_TryCatch(), and after that it is caught and handled by JavascriptGenerator::CallGenerator().

But when we run with -debuglaunch the exception gets caught by InterpreterStackFrame::DebugProcess(), which does not rethrow it. Therefore the generator code does not have a chance to complete correctly and the process crashes because an invalid var is returned in place of a generator yielded object.

As fix this PR adds a check for IsGeneratorReturnException() in InterpreterStackFrame::DebugProcess() to avoid skipping this exception.

Author: paolosevMSFT

lib/Runtime/Language/InterpreterStackFrame.cpp

@@ -2353,8 +2353,9 @@ namespace Js
             if (exception)
             {
                 bool skipException = false;
-                if (exception != scriptContext->GetThreadContext()->GetPendingSOErrorObject()
-                    && exception != scriptContext->GetThreadContext()->GetPendingOOMErrorObject())
+                if (!exception->IsGeneratorReturnException() &&
+                    exception != scriptContext->GetThreadContext()->GetPendingSOErrorObject() &&
+                    exception != scriptContext->GetThreadContext()->GetPendingOOMErrorObject())
                 {
                     skipException = exception->IsDebuggerSkip();
                 }

test/DebuggerCommon/generators.js

@@ -124,12 +124,28 @@ g = gf4(); /**bp:
 
                 stack();resume('step_into');
                 stack();resume('step_into');
-                stack();resume('step_into');
-                stack();resume('step_out');
-                stack();resume('step_out');
             **/
 
 g.next(1);
 g.return(2);
 
+function* gf5() {
+    try {
+        yield 32;
+    } catch (e) {
+    }
+}
+
+g = gf5(); /**bp:
+                stack();resume('step_over');
+
+                resume('step_over');
+
+                stack();resume('step_into');
+                stack();resume('step_out');
+                stack();
+            **/
+g.next();
+g.return(1);
+
 WScript.Echo("PASS");

test/DebuggerCommon/generators.js.dbg.baseline

@@ -524,7 +524,7 @@
   {
     "callStack": [
       {
-        "line": 132,
+        "line": 129,
         "column": 0,
         "sourceText": "g.return(2)",
         "function": "Global code"
@@ -540,7 +540,7 @@
         "function": "gf4"
       },
       {
-        "line": 132,
+        "line": 129,
         "column": 0,
         "sourceText": "g.return(2)",
         "function": "Global code"
@@ -550,59 +550,45 @@
   {
     "callStack": [
       {
-        "line": 77,
-        "column": 4,
-        "sourceText": "yield 1",
-        "function": "gf3"
-      },
-      {
-        "line": 82,
-        "column": 4,
-        "sourceText": "yield* gf3()",
-        "function": "gf4"
-      },
-      {
-        "line": 132,
+        "line": 138,
         "column": 0,
-        "sourceText": "g.return(2)",
+        "sourceText": "g = gf5()",
         "function": "Global code"
       }
     ]
   },
   {
     "callStack": [
       {
-        "line": 78,
-        "column": 4,
-        "sourceText": "yield 2",
-        "function": "gf3"
-      },
+        "line": 148,
+        "column": 0,
+        "sourceText": "g.return(1)",
+        "function": "Global code"
+      }
+    ]
+  },
+  {
+    "callStack": [
       {
-        "line": 82,
-        "column": 4,
-        "sourceText": "yield* gf3()",
-        "function": "gf4"
+        "line": 133,
+        "column": 8,
+        "sourceText": "yield 32",
+        "function": "gf5"
       },
       {
-        "line": 132,
+        "line": 148,
         "column": 0,
-        "sourceText": "g.return(2)",
+        "sourceText": "g.return(1)",
         "function": "Global code"
       }
     ]
   },
   {
     "callStack": [
       {
-        "line": 82,
-        "column": 4,
-        "sourceText": "yield* gf3()",
-        "function": "gf4"
-      },
-      {
-        "line": 132,
+        "line": 150,
         "column": 0,
-        "sourceText": "g.return(2)",
+        "sourceText": "WScript.Echo(\"PASS\")",
         "function": "Global code"
       }
     ]

test/es6/generators-functionality.js

@@ -949,6 +949,11 @@ var tests = [
             assert.areEqual({ value: 2, done: false }, g.return(100), "Return causes the finally block to execute");
             assert.throws(function () { g.next(); }, ExpectedException, "Second next call should throw from finally block");
             assert.areEqual({ value: undefined, done: true }, g.next(), "Method execution has finished");
+
+            gf = function* () { try { throw new ExpectedException(); } catch (e) { throw e; } }
+            g = gf();
+            assert.throws(function () { g.next() }, ExpectedException, "First next call should rethrow exception");
+            assert.areEqual({ value: 2, done: true }, g.return(2), "Return statement completes the function from try block");
         }
     },
     {