Bug 996060 - Part 2: Add a testing function and jit test for pending exception's stacks; r=sfink

js/src/builtin/TestingFunctions.cpp

@@ -3495,6 +3495,40 @@ GetModuleEnvironmentValue(JSContext* cx, unsigned argc, Value* vp)
     return GetProperty(cx, env, env, id, args.rval());
 }
 
+static bool
+CatchAndReturnPendingExceptionStack(JSContext* cx, unsigned argc, Value* vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+    if (args.length() != 1) {
+        JS_ReportError(cx, "Wrong number of arguments, expected exactly 1");
+        return false;
+    }
+
+    if (!args[0].isObject() || !IsCallable(args[0])) {
+        JS_ReportError(cx, "Argument must be callable");
+        return false;
+    }
+
+    RootedValue thisv(cx, NullValue());
+    RootedObject fun(cx, &args[0].toObject());
+    RootedValue rval(cx);
+    if (JS::Call(cx, UndefinedHandleValue, fun, JS::HandleValueArray::empty(), &rval) ||
+        !cx->isExceptionPending())
+    {
+        JS_ReportError(cx, "Supplied callable did not throw");
+        return false;
+    }
+
+    RootedObject stack(cx);
+    if (!JS::GetPendingExceptionStack(cx, &stack))
+        return false;
+    cx->clearPendingException();
+
+    MOZ_ASSERT_IF(stack, stack->is<SavedFrame>());
+    args.rval().setObjectOrNull(stack);
+    return true;
+}
+
 static const JSFunctionSpecWithHelp TestingFunctions[] = {
     JS_FN_HELP("gc", ::GC, 0, 0,
 "gc([obj] | 'compartment' [, 'shrinking'])",
@@ -4012,6 +4046,11 @@ gc::ZealModeHelpText),
 "getModuleEnvironmentValue(module, name)",
 "  Get the value of a bound name in a module environment.\n"),
 
+    JS_FN_HELP("catchAndReturnPendingExceptionStack", CatchAndReturnPendingExceptionStack, 1, 0,
+"catchAndReturnPendingExceptionStack(func)",
+"  Call `func`, catch its thrown exception, and return the stack captured when\n"
+"  the exception was thrown.\n"),
+
     JS_FS_HELP_END
 };
 

js/src/jit-test/tests/basic/pending-exception-stack-2.js

@@ -0,0 +1,20 @@
+let err;
+const stack = catchAndReturnPendingExceptionStack(function a() {
+  err = new Error();
+  (function b() {
+    (function c() {
+      throw err;
+    }());
+  }());
+});
+
+assertEq(!!err, true);
+
+// Yes, they're different!
+assertEq(stack.toString() != err.stack, true);
+
+assertEq(stack.functionDisplayName, "c");
+assertEq(stack.parent.functionDisplayName, "b");
+assertEq(stack.parent.parent.functionDisplayName, "a");
+assertEq(stack.parent.parent.parent.functionDisplayName, null);
+assertEq(stack.parent.parent.parent.parent, null);

js/src/jit-test/tests/basic/pending-exception-stack.js

@@ -0,0 +1,13 @@
+const stack = catchAndReturnPendingExceptionStack(function a() {
+  (function b() {
+    (function c() {
+      throw 42;
+    }());
+  }());
+});
+
+assertEq(stack.functionDisplayName, "c");
+assertEq(stack.parent.functionDisplayName, "b");
+assertEq(stack.parent.parent.functionDisplayName, "a");
+assertEq(stack.parent.parent.parent.functionDisplayName, null);
+assertEq(stack.parent.parent.parent.parent, null);