Allow stepping into Object.observe handlers.

BUG=chromium:432468
R=yangguo@chromium.org, adamk@chromium.org
LOG=N

Review URL: https://codereview.chromium.org/739523002

Cr-Commit-Position: refs/heads/master@{#25423}

src/debug.h

@@ -503,6 +503,8 @@ class Debug {
     return reinterpret_cast<Address>(&thread_local_.step_into_fp_);
   }
 
+  StepAction last_step_action() { return thread_local_.last_step_action_; }
+
  private:
   explicit Debug(Isolate* isolate);
 

src/runtime/runtime-debug.cc

@@ -2731,7 +2731,9 @@ RUNTIME_FUNCTION(Runtime_GetScript) {
 // to a built-in function such as Array.forEach.
 RUNTIME_FUNCTION(Runtime_DebugCallbackSupportsStepping) {
   DCHECK(args.length() == 1);
-  if (!isolate->debug()->is_active() || !isolate->debug()->StepInActive()) {
+  Debug* debug = isolate->debug();
+  if (!debug->is_active() || !debug->IsStepping() ||
+      debug->last_step_action() != StepIn) {
     return isolate->heap()->false_value();
   }
   CONVERT_ARG_CHECKED(Object, callback, 0);

src/runtime/runtime-observe.cc

@@ -5,6 +5,7 @@
 #include "src/v8.h"
 
 #include "src/arguments.h"
+#include "src/debug.h"
 #include "src/runtime/runtime-utils.h"
 
 namespace v8 {
@@ -63,6 +64,18 @@ RUNTIME_FUNCTION(Runtime_DeliverObservationChangeRecords) {
   // we make a call inside a verbose TryCatch.
   catcher.SetVerbose(true);
   Handle<Object> argv[] = {argument};
+
+  // Allow stepping into the observer callback.
+  Debug* debug = isolate->debug();
+  if (debug->is_active() && debug->IsStepping() &&
+      debug->last_step_action() == StepIn) {
+    // Previous StepIn may have activated a StepOut if it was at the frame exit.
+    // In this case to be able to step into the callback again, we need to clear
+    // the step out first.
+    debug->ClearStepOut();
+    debug->FloodWithOneShot(callback);
+  }
+
   USE(Execution::Call(isolate, callback, isolate->factory()->undefined_value(),
                       arraysize(argv), argv));
   if (isolate->has_pending_exception()) {

test/mjsunit/debug-stepin-foreach.js

@@ -0,0 +1,51 @@
+// Copyright 2014 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --expose-debug-as debug
+// Tests stepping into through Array.prototype.forEach callbacks.
+
+Debug = debug.Debug
+var exception = null;
+var break_count = 0;
+var expected_breaks = -1;
+
+function listener(event, exec_state, event_data, data) {
+  try {
+    if (event == Debug.DebugEvent.Break) {
+      assertTrue(exec_state.frameCount() != 0, "FAIL: Empty stack trace");
+      if (!break_count) {
+        // Count number of expected breakpoints in this source file.
+        var source_text = exec_state.frame(0).func().script().source();
+        expected_breaks = source_text.match(/\/\/\s*Break\s+\d+\./g).length;
+        print("Expected breaks: " + expected_breaks);
+      }
+      var source = exec_state.frame(0).sourceLineText();
+      print("paused at: " + source);
+      assertTrue(source.indexOf("// Break " + break_count + ".") > 0,
+                 "Unexpected pause at: " + source + "\n" +
+                 "Expected: // Break " + break_count + ".");
+      ++break_count;
+      if (break_count !== expected_breaks) {
+        exec_state.prepareStep(Debug.StepAction.StepIn, 1);
+      }
+    }
+  } catch(e) {
+    exception = e;
+    print(e, e.stack);
+  }
+};
+
+Debug.setListener(listener);
+
+debugger; // Break 0.
+[1,2].forEach(callback); // Break 1.
+
+function callback(x) {
+  return x; // Break 2. // Break 4.
+} // Break 3. // Break 5.
+
+assertNull(exception); // Break 6.
+assertEquals(expected_breaks, break_count);
+
+Debug.setListener(null);

test/mjsunit/es6/debug-stepin-microtasks.js

@@ -7,27 +7,29 @@
 Debug = debug.Debug
 var exception = null;
 var break_count = 0;
-var expected_breaks = 7;
+var expected_breaks = -1;
 
 function listener(event, exec_state, event_data, data) {
   try {
     if (event == Debug.DebugEvent.Break) {
       assertTrue(exec_state.frameCount() != 0, "FAIL: Empty stack trace");
+      if (!break_count) {
+        // Count number of expected breakpoints in this source file.
+        var source_text = exec_state.frame(0).func().script().source();
+        expected_breaks = source_text.match(/\/\/\s*Break\s+\d+\./g).length;
+        print("Expected breaks: " + expected_breaks);
+      }
       var source = exec_state.frame(0).sourceLineText();
       print("paused at: " + source);
       assertTrue(source.indexOf("// Break " + break_count + ".") > 0,
-                 "Unexpected pause at: " + source);
+                 "Unexpected pause at: " + source + "\n" +
+                 "Expected: // Break " + break_count + ".");
       if (source.indexOf("StepOver.") !== -1) {
         exec_state.prepareStep(Debug.StepAction.StepNext, 1);
       } else {
         exec_state.prepareStep(Debug.StepAction.StepIn, 1);
       }
       ++break_count;
-    } else if (event == Debug.DebugEvent.AsyncTaskEvent &&
-               event_data.type() === "willHandle" &&
-               event_data.name() !== "Object.observe" &&
-               break_count > 0) {
-      exec_state.prepareStep(Debug.StepAction.StepIn, 1);
     }
   } catch (e) {
     exception = e;
@@ -42,30 +44,49 @@ Promise.resolve(42)
   .then(Object) // Should skip stepping into native.
   .then(Boolean) // Should skip stepping into native.
   .then(promise2)
-  .then(undefined, promise3)
+  .catch(promise3)
   .catch(function(e) {
     %AbortJS("FAIL: uncaught exception " + e);
   });
 
-function promise1()
-{
+function promise1() {
   debugger; // Break 0.
   return exception || 1; // Break 1.
 } // Break 2.
 
-function promise2()
-{
+function promise2() {
   throw new Error; // Break 3.
 }
 
-function promise3()
-{
-  finalize(); // Break 4. StepOver.
+function promise3() {
+  installObservers(); // Break 4. StepOver.
   return break_count; // Break 5.
 } // Break 6.
 
-function finalize()
-{
+function installObservers() {
+  var dummy = {};
+  Object.observe(dummy, observer1);
+  Object.observe(dummy, Object); // Should skip stepping into native.
+  Object.observe(dummy, Boolean); // Should skip stepping into native.
+  Object.observe(dummy, observer2);
+  dummy.foo = 1;
+}
+
+function observer1() {
+  return exception || 3; // Break 7.
+} // Break 8.
+
+function observer2() {
+  Promise.resolve().then(promise4); // Break 9. StepOver.
+  return break_count + 1; // Break 10.
+} // Break 11.
+
+function promise4() {
+  finalize(); // Break 12. StepOver.
+  return 0; // Break 13.
+} // Break 14. StepOver.
+
+function finalize() {
   var dummy = {};
   Object.observe(dummy, function() {
     if (expected_breaks !== break_count) {