Index: lldb/trunk/packages/Python/lldbsuite/test/functionalities/data-formatter/data-formatter-stl/libcxx/optional/Makefile
===================================================================
--- lldb/trunk/packages/Python/lldbsuite/test/functionalities/data-formatter/data-formatter-stl/libcxx/optional/Makefile
+++ lldb/trunk/packages/Python/lldbsuite/test/functionalities/data-formatter/data-formatter-stl/libcxx/optional/Makefile
@@ -0,0 +1,7 @@
+LEVEL = ../../../../../make
+
+CXX_SOURCES := main.cpp
+
+USE_LIBCPP := 1
+include $(LEVEL)/Makefile.rules
+CXXFLAGS += -std=c++17
Index: lldb/trunk/packages/Python/lldbsuite/test/functionalities/data-formatter/data-formatter-stl/libcxx/optional/TestDataFormatterLibcxxOptional.py
===================================================================
--- lldb/trunk/packages/Python/lldbsuite/test/functionalities/data-formatter/data-formatter-stl/libcxx/optional/TestDataFormatterLibcxxOptional.py
+++ lldb/trunk/packages/Python/lldbsuite/test/functionalities/data-formatter/data-formatter-stl/libcxx/optional/TestDataFormatterLibcxxOptional.py
@@ -0,0 +1,59 @@
+"""
+Test lldb data formatter subsystem.
+"""
+
+from __future__ import print_function
+
+
+import os
+import time
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class LibcxxOptionalDataFormatterTestCase(TestBase):
+
+    mydir = TestBase.compute_mydir(__file__)
+
+    @add_test_categories(["libc++"])
+
+    def test_with_run_command(self):
+        """Test that that file and class static variables display correctly."""
+        self.build()
+        self.runCmd("file " + self.getBuildArtifact("a.out"), CURRENT_EXECUTABLE_SET)
+
+        bkpt = self.target().FindBreakpointByID(
+            lldbutil.run_break_set_by_source_regexp(
+                self, "break here"))
+
+        self.runCmd("run", RUN_SUCCEEDED)
+
+        # The stop reason of the thread should be breakpoint.
+        self.expect("thread list", STOPPED_DUE_TO_BREAKPOINT,
+                    substrs=['stopped',
+                             'stop reason = breakpoint'])
+
+        self.expect("frame variable number_not_engaged",
+                    substrs=['Has Value=false'])
+
+        self.expect("frame variable number_engaged",
+                    substrs=['Has Value=true',
+                             'Value = 42',
+                             '}'])
+
+        self.expect("frame var numbers",
+                    substrs=['(optional_int_vect) numbers =  Has Value=true  {',
+                             'Value = size=4 {',
+                               '[0] = 1',
+                               '[1] = 2',
+                               '[2] = 3',
+                               '[3] = 4',
+                               '}',
+                             '}'])
+
+        self.expect("frame var ostring",
+                    substrs=['(optional_string) ostring =  Has Value=true  {',
+                        'Value = "hello"',
+                        '}'])
Index: lldb/trunk/packages/Python/lldbsuite/test/functionalities/data-formatter/data-formatter-stl/libcxx/optional/main.cpp
===================================================================
--- lldb/trunk/packages/Python/lldbsuite/test/functionalities/data-formatter/data-formatter-stl/libcxx/optional/main.cpp
+++ lldb/trunk/packages/Python/lldbsuite/test/functionalities/data-formatter/data-formatter-stl/libcxx/optional/main.cpp
@@ -0,0 +1,27 @@
+#include <cstdio>
+#include <string>
+#include <vector>
+#include <optional>
+
+using int_vect = std::vector<int> ;
+using optional_int = std::optional<int> ;
+using optional_int_vect = std::optional<int_vect> ;
+using optional_string = std::optional<std::string> ;
+
+int main()
+{
+    optional_int number_not_engaged ;
+    optional_int number_engaged = 42 ;
+
+    printf( "%d\n", *number_engaged) ;
+
+    optional_int_vect numbers{{1,2,3,4}} ;
+
+    printf( "%d %d\n", numbers.value()[0], numbers.value()[1] ) ;
+
+    optional_string ostring = "hello" ;
+
+    printf( "%s\n", ostring->c_str() ) ;
+
+    return 0; // break here
+}
Index: lldb/trunk/source/Plugins/Language/CPlusPlus/LibCxxOptional.cpp
===================================================================
--- lldb/trunk/source/Plugins/Language/CPlusPlus/LibCxxOptional.cpp
+++ lldb/trunk/source/Plugins/Language/CPlusPlus/LibCxxOptional.cpp
@@ -0,0 +1,85 @@
+//===-- LibCxxOptional.cpp --------------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "LibCxx.h"
+#include "lldb/DataFormatters/FormattersHelpers.h"
+
+using namespace lldb;
+using namespace lldb_private;
+
+namespace {
+
+class OptionalFrontEnd : public SyntheticChildrenFrontEnd {
+public:
+  OptionalFrontEnd(ValueObject &valobj) : SyntheticChildrenFrontEnd(valobj) {
+    Update();
+  }
+
+  size_t GetIndexOfChildWithName(const ConstString &name) override {
+    return formatters::ExtractIndexFromString(name.GetCString());
+  }
+
+  bool MightHaveChildren() override { return true; }
+  bool Update() override;
+  size_t CalculateNumChildren() override { return m_size; }
+  ValueObjectSP GetChildAtIndex(size_t idx) override;
+
+private:
+  size_t m_size = 0;
+  ValueObjectSP m_base_sp;
+};
+} // namespace
+
+bool OptionalFrontEnd::Update() {
+  ValueObjectSP engaged_sp(
+      m_backend.GetChildMemberWithName(ConstString("__engaged_"), true));
+
+  if (!engaged_sp)
+    return false;
+
+  // __engaged_ is a bool flag and is true if the optional contains a value.
+  // Converting it to unsigned gives us a size of 1 if it contains a value
+  // and 0 if not.
+  m_size = engaged_sp->GetValueAsUnsigned(0);
+
+  return false;
+}
+
+ValueObjectSP OptionalFrontEnd::GetChildAtIndex(size_t idx) {
+  if (idx >= m_size)
+    return ValueObjectSP();
+
+  // __val_ contains the underlying value of an optional if it has one.
+  // Currently because it is part of an anonymous union GetChildMemberWithName()
+  // does not peer through and find it unless we are at the parent itself.
+  // We can obtain the parent through __engaged_.
+  ValueObjectSP val_sp(
+      m_backend.GetChildMemberWithName(ConstString("__engaged_"), true)
+          ->GetParent()
+          ->GetChildAtIndex(0, true)
+          ->GetChildMemberWithName(ConstString("__val_"), true));
+
+  if (!val_sp)
+    return ValueObjectSP();
+
+  CompilerType holder_type = val_sp->GetCompilerType();
+
+  if (!holder_type)
+    return ValueObjectSP();
+
+  return val_sp->Clone(ConstString(llvm::formatv("Value").str()));
+}
+
+SyntheticChildrenFrontEnd *
+formatters::LibcxxOptionalFrontEndCreator(CXXSyntheticChildren *,
+                                          lldb::ValueObjectSP valobj_sp) {
+  if (valobj_sp)
+    return new OptionalFrontEnd(*valobj_sp);
+  return nullptr;
+}