[debugger] add utility to print break location.

src/debug/debug.cc

 // Copyright 2012 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.
 
 #include "src/debug/debug.h"
 
 #include "src/api.h"
 #include "src/arguments.h"
 #include "src/bootstrapper.h"
 #include "src/code-stubs.h"
@@ skipping 1835 matching lines @@
   // Return to continue execution from where the exception was thrown.
 }
 
 
 void Debug::OnDebugBreak(Handle<Object> break_points_hit, bool auto_continue) {
   // The caller provided for DebugScope.
   AssertDebugContext();
   // Bail out if there is no listener for this event
   if (ignore_events()) return;
 
+#ifdef DEBUG
+  PrintBreakLocation();
+#endif  // DEBUG
+
   HandleScope scope(isolate_);
   // Create the event data object.
   Handle<Object> event_data;
   // Bail out and don't call debugger if exception.
   if (!MakeBreakEvent(break_points_hit).ToHandle(&event_data)) return;
 
   // Process debug event.
   ProcessDebugEvent(v8::Break,
                     Handle<JSObject>::cast(event_data),
                     auto_continue);
@@ skipping 441 matching lines @@
 
   HandleScope scope(isolate_);
   DebugScope debug_scope(this);
   if (debug_scope.failed()) return;
 
   // Notify the debug event listeners. Indicate auto continue if the break was
   // a debug command break.
   OnDebugBreak(isolate_->factory()->undefined_value(), debug_command_only);
 }
 
+#ifdef DEBUG
+void Debug::PrintBreakLocation() {
+  if (!FLAG_print_break_location) return;
+  HandleScope scope(isolate_);
+  JavaScriptFrameIterator iterator(isolate_);
+  if (iterator.done()) return;
+  JavaScriptFrame* frame = iterator.frame();
+  FrameSummary summary = GetFirstFrameSummary(frame);
+  int source_position =
+      summary.abstract_code()->SourcePosition(summary.code_offset());
+  Handle<Object> script_obj(summary.function()->shared()->script(), isolate_);
+  PrintF("[debug] break in function '");
+  summary.function()->PrintName();
+  PrintF("'.\n");
+  if (script_obj->IsScript()) {
+    Handle<Script> script = Handle<Script>::cast(script_obj);
+    Handle<String> source(String::cast(script->source()));
+    Script::InitLineEnds(script);
+    int line = Script::GetLineNumber(script, source_position);
+    int column = Script::GetColumnNumber(script, source_position);
+    Handle<FixedArray> line_ends(FixedArray::cast(script->line_ends()));
+    int line_start =
+        line == 0 ? 0 : Smi::cast(line_ends->get(line - 1))->value();
+    int line_end = Smi::cast(line_ends->get(line))->value();
+    DisallowHeapAllocation no_gc;
+    String::FlatContent content = source->GetFlatContent();
+    if (content.IsOneByte()) {
+      PrintF("[debug] %.*s\n", line_end - line_start,
+             content.ToOneByteVector().start() + line_start);
+      PrintF("[debug] ");
+      for (int i = 0; i < column; i++) PrintF(" ");
+      PrintF("^\n");
+    } else {
+      PrintF("[debug] at line %d column %d\n", line, column);
+    }
+  }
+}
+#endif  // DEBUG
 
 DebugScope::DebugScope(Debug* debug)
     : debug_(debug),
       prev_(debug->debugger_entry()),
       save_(debug_->isolate_),
       no_termination_exceptons_(debug_->isolate_,
                                 StackGuard::TERMINATE_EXECUTION) {
   // Link recursive debugger entry.
   base::NoBarrier_Store(&debug_->thread_local_.current_debug_scope_,
                         reinterpret_cast<base::AtomicWord>(this));
@@ skipping 290 matching lines @@
 }
 
 
 void LockingCommandMessageQueue::Clear() {
   base::LockGuard<base::Mutex> lock_guard(&mutex_);
   queue_.Clear();
 }
 
 }  // namespace internal
 }  // namespace v8