Small improvements in debugging experience on Windows

If running under debugger:
1. Output from _v8_internal_Print_Object into debugger's command window
2. Break into debugger before aborting

Change-Id: I49e4d83c817e6588c4679c9fb9766602927542db
Reviewed-on: https://chromium-review.googlesource.com/c/1435771
Commit-Queue: Irina Yatsenko <irinayat@microsoft.com>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59137}

src/base/platform/platform-win32.cc

@@ -920,6 +920,11 @@ void OS::Sleep(TimeDelta interval) {
 
 
 void OS::Abort() {
+  // Give a chance to debug the failure.
+  if (IsDebuggerPresent()) {
+    DebugBreak();
+  }
+
   // Before aborting, make sure to flush output buffers.
   fflush(stdout);
   fflush(stderr);

src/objects-printer.cc

@@ -69,6 +69,11 @@ namespace internal {
 #ifdef OBJECT_PRINT
 
 void Object::Print() const {
+  // Output into debugger's command window if a debugger is attached.
+  DbgStdoutStream dbg_os;
+  this->Print(dbg_os);
+  dbg_os << std::flush;
+
   StdoutStream os;
   this->Print(os);
   os << std::flush;

src/ostreams.cc

@@ -7,6 +7,7 @@
 #include "src/objects/string.h"
 
 #if V8_OS_WIN
+#include <windows.h>
 #if _MSC_VER < 1900
 #define snprintf sprintf_s
 #endif
@@ -20,6 +21,48 @@
 namespace v8 {
 namespace internal {
 
+DbgStreamBuf::DbgStreamBuf() { setp(data_, data_ + sizeof(data_)); }
+
+DbgStreamBuf::~DbgStreamBuf() { sync(); }
+
+int DbgStreamBuf::overflow(int c) {
+#if V8_OS_WIN
+  if (!IsDebuggerPresent()) {
+    return 0;
+  }
+
+  sync();
+
+  if (c != EOF) {
+    if (pbase() == epptr()) {
+      auto as_char = static_cast<char>(c);
+      OutputDebugStringA(&as_char);
+    } else {
+      sputc(static_cast<char>(c));
+    }
+  }
+#endif
+  return 0;
+}
+
+int DbgStreamBuf::sync() {
+#if V8_OS_WIN
+  if (!IsDebuggerPresent()) {
+    return 0;
+  }
+
+  if (pbase() != pptr()) {
+    OutputDebugStringA(
+      std::string(pbase(),
+      static_cast<std::string::size_type>(pptr() - pbase())).c_str());
+    setp(pbase(), epptr());
+  }
+#endif
+  return 0;
+}
+
+DbgStdoutStream::DbgStdoutStream() : std::ostream(&streambuf_) {}
+
 OFStreamBase::OFStreamBase(FILE* f) : f_(f) {}
 
 int OFStreamBase::sync() {

src/ostreams.h

@@ -31,6 +31,28 @@ class V8_EXPORT_PRIVATE OFStreamBase : public std::streambuf {
   std::streamsize xsputn(const char* s, std::streamsize n) override;
 };
 
+// Output buffer and stream writing into debugger's command window.
+class V8_EXPORT_PRIVATE DbgStreamBuf : public std::streambuf {
+ public:
+  DbgStreamBuf();
+  ~DbgStreamBuf();
+
+ private:
+  int sync() override;
+  int overflow(int c) override;
+
+  char data_[256];
+};
+
+class DbgStdoutStream : public std::ostream {
+ public:
+  DbgStdoutStream();
+  ~DbgStdoutStream() = default;
+
+ private:
+  DbgStreamBuf streambuf_;
+};
+
 // An output stream writing to a file.
 class V8_EXPORT_PRIVATE OFStream : public std::ostream {
  public: