Convert FileSystem::Open() to return Expected<FileUP>

Summary:
This patch converts FileSystem::Open from this prototype:

Status
Open(File &File, const FileSpec &file_spec, ...);

to this one:

llvm::Expected<std::unique_ptr<File>>
Open(const FileSpec &file_spec, ...);

This is beneficial on its own, as llvm::Expected is a more modern
and recommended error type than Status.  It is also a necessary step
towards https://reviews.llvm.org/D67891, and further developments
for lldb_private::File.

Reviewers: JDevlieghere, jasonmolenda, labath

Reviewed By: labath

Subscribers: mgorny, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D67996

llvm-svn: 373003

lldb/source/Plugins/ScriptInterpreter/Python/PythonDataObjects.cpp

@@ -949,11 +949,6 @@ PythonFile::PythonFile() : PythonObject() {}
 
 PythonFile::PythonFile(File &file, const char *mode) { Reset(file, mode); }
 
-PythonFile::PythonFile(const char *path, const char *mode) {
-  lldb_private::File file;
-  FileSystem::Instance().Open(file, FileSpec(path), GetOptionsFromMode(mode));
-  Reset(file, mode);
-}
 
 PythonFile::PythonFile(PyRefType type, PyObject *o) { Reset(type, o); }
 
@@ -1036,17 +1031,19 @@ uint32_t PythonFile::GetOptionsFromMode(llvm::StringRef mode) {
       .Default(0);
 }
 
-bool PythonFile::GetUnderlyingFile(File &file) const {
+FileUP PythonFile::GetUnderlyingFile() const {
   if (!IsValid())
-    return false;
+    return nullptr;
 
-  file.Close();
   // We don't own the file descriptor returned by this function, make sure the
   // File object knows about that.
   PythonString py_mode = GetAttributeValue("mode").AsType<PythonString>();
   auto options = PythonFile::GetOptionsFromMode(py_mode.GetString());
-  file.SetDescriptor(PyObject_AsFileDescriptor(m_py_obj), options, false);
-  return file.IsValid();
+  auto file = std::make_unique<File>(PyObject_AsFileDescriptor(m_py_obj),
+                                     options, false);
+  if (!file->IsValid())
+    return nullptr;
+  return file;
 }
 
 #endif