[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/packages/Python/lldbsuite/test/python_api/file_handle/TestFileHandle.py

@@ -845,11 +845,16 @@ class FileHandleTestCase(lldbtest.TestBase):
             def i(sbf):
                 for i in range(10):
                     f = sbf.GetFile()
+                    self.assertEqual(f.mode, "w")
                     yield f
                     sbf = lldb.SBFile.Create(f, borrow=True)
                     yield sbf
                     sbf.Write(str(i).encode('ascii') + b"\n")
             files = list(i(sbf))
+            # delete them in reverse order, again because each is a borrow
+            # of the previous.
+            while files:
+                files.pop()
         with open(self.out_filename, 'r') as f:
             self.assertEqual(list(range(10)), list(map(int, f.read().strip().split())))
 

lldb/source/Host/common/File.cpp

@@ -310,7 +310,7 @@ Status NativeFile::Close() {
     if (m_own_stream) {
       if (::fclose(m_stream) == EOF)
         error.SetErrorToErrno();
-    } else {
+    } else if (m_options & eOpenOptionWrite) {
       if (::fflush(m_stream) == EOF)
         error.SetErrorToErrno();
     }

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)

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

@@ -189,6 +189,14 @@ inline llvm::Error keyError() {
                                  "key not in dict");
 }
 
+#if PY_MAJOR_VERSION < 3
+// The python 2 API declares some arguments as char* that should
+// be const char *, but it doesn't actually modify them.
+inline char *py2_const_cast(const char *s) { return const_cast<char *>(s); }
+#else
+inline const char *py2_const_cast(const char *s) { return s; }
+#endif
+
 enum class PyInitialValue { Invalid, Empty };
 
 template <typename T, typename Enable = void> struct PythonFormat;
@@ -309,16 +317,6 @@ public:
 
   StructuredData::ObjectSP CreateStructuredObject() const;
 
-protected:
-
-#if PY_MAJOR_VERSION < 3
-  // The python 2 API declares some arguments as char* that should
-  // be const char *, but it doesn't actually modify them.
-  static char *py2_const_cast(const char *s) { return const_cast<char *>(s); }
-#else
-  static const char *py2_const_cast(const char *s) { return s; }
-#endif
-
 public:
   template <typename... T>
   llvm::Expected<PythonObject> CallMethod(const char *name,