[PUSHED 1/6] gdb/python: convert gdbpy_err_fetch to use gdbpy_ref

[Andrew Burgess <aburgess@redhat.com>]

Convert the gdbpy_err_fetch class to make use of gdbpy_ref, this
removes the need for manual reference count management, and allows the
destructor to be removed.

There should be no functional change after this commit.

I think this cleanup is worth doing on its own, however, in a later
commit I will want to copy instances of gdbpy_err_fetch, and switching
to using gdbpy_ref means that I can rely on the default copy
constructor, without having to add one that handles the reference
counts, so this is good preparation for that upcoming change.
---
 gdb/python/py-utils.c        |  8 ++++----
 gdb/python/python-internal.h | 23 ++++++++++-------------
 2 files changed, 14 insertions(+), 17 deletions(-)

diff --git a/gdb/python/py-utils.c b/gdb/python/py-utils.c
index 1bd7b477ecb..58c18c60e2c 100644
--- a/gdb/python/py-utils.c
+++ b/gdb/python/py-utils.c
@@ -194,10 +194,10 @@ gdbpy_err_fetch::to_string () const
      Using str (aka PyObject_Str) will fetch the error message from
      gdb.GdbError ("message").  */
 
-  if (m_error_value && m_error_value != Py_None)
-    return gdbpy_obj_to_string (m_error_value);
+  if (m_error_value.get () != nullptr && m_error_value.get () != Py_None)
+    return gdbpy_obj_to_string (m_error_value.get ());
   else
-    return gdbpy_obj_to_string (m_error_type);
+    return gdbpy_obj_to_string (m_error_type.get ());
 }
 
 /* See python-internal.h.  */
@@ -205,7 +205,7 @@ gdbpy_err_fetch::to_string () const
 gdb::unique_xmalloc_ptr<char>
 gdbpy_err_fetch::type_to_string () const
 {
-  return gdbpy_obj_to_string (m_error_type);
+  return gdbpy_obj_to_string (m_error_type.get ());
 }
 
 /* Convert a GDB exception to the appropriate Python exception.
diff --git a/gdb/python/python-internal.h b/gdb/python/python-internal.h
index 217bc15bb28..da2e79101a6 100644
--- a/gdb/python/python-internal.h
+++ b/gdb/python/python-internal.h
@@ -549,14 +549,12 @@ class gdbpy_err_fetch
 
   gdbpy_err_fetch ()
   {
-    PyErr_Fetch (&m_error_type, &m_error_value, &m_error_traceback);
-  }
+    PyObject *error_type, *error_value, *error_traceback;
 
-  ~gdbpy_err_fetch ()
-  {
-    Py_XDECREF (m_error_type);
-    Py_XDECREF (m_error_value);
-    Py_XDECREF (m_error_traceback);
+    PyErr_Fetch (&error_type, &error_value, &error_traceback);
+    m_error_type.reset (error_type);
+    m_error_value.reset (error_value);
+    m_error_traceback.reset (error_traceback);
   }
 
   /* Call PyErr_Restore using the values stashed in this object.
@@ -565,10 +563,9 @@ class gdbpy_err_fetch
 
   void restore ()
   {
-    PyErr_Restore (m_error_type, m_error_value, m_error_traceback);
-    m_error_type = nullptr;
-    m_error_value = nullptr;
-    m_error_traceback = nullptr;
+    PyErr_Restore (m_error_type.release (),
+		   m_error_value.release (),
+		   m_error_traceback.release ());
   }
 
   /* Return the string representation of the exception represented by
@@ -587,12 +584,12 @@ class gdbpy_err_fetch
 
   bool type_matches (PyObject *type) const
   {
-    return PyErr_GivenExceptionMatches (m_error_type, type);
+    return PyErr_GivenExceptionMatches (m_error_type.get (), type);
   }
 
 private:
 
-  PyObject *m_error_type, *m_error_value, *m_error_traceback;
+  gdbpy_ref<> m_error_type, m_error_value, m_error_traceback;
 };
 
 /* Called before entering the Python interpreter to install the
-- 
2.25.4