[LLDB][Python] fix another fflush issue on NetBSD

Summary:
Here's another instance where we were calling fflush on an input
stream, which is illegal on NetBSD.

Reviewers: labath, mgorny

Reviewed By: mgorny

Subscribers: krytarowski, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D69488

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

@@ -1502,12 +1502,19 @@ Expected<PythonFile> PythonFile::FromFile(File &file, const char *mode) {
   file_obj = PyFile_FromFd(file.GetDescriptor(), nullptr, mode, -1, nullptr,
                            "ignore", nullptr, 0);
 #else
-  // Read through the Python source, doesn't seem to modify these strings
-  char *cmode = const_cast<char *>(mode);
   // We pass ::flush instead of ::fclose here so we borrow the FILE* --
-  // the lldb_private::File still owns it.
-  file_obj =
-      PyFile_FromFile(file.GetStream(), const_cast<char *>(""), cmode, ::fflush);
+  // the lldb_private::File still owns it.   NetBSD does not allow
+  // input files to be flushed, so we have to check for that case too.
+  int (*closer)(FILE *);
+  auto opts = file.GetOptions();
+  if (!opts)
+    return opts.takeError();
+  if (opts.get() & File::eOpenOptionWrite)
+    closer = ::fflush;
+  else
+    closer = [](FILE *) { return 0; };
+  file_obj = PyFile_FromFile(file.GetStream(), py2_const_cast(""),
+                             py2_const_cast(mode), closer);
 #endif
 
   if (!file_obj)