Use a wrapper for PyErr_Fetch

This introduces a new class that wraps PyErr_Fetch and PyErr_Restore,
and then changes all the callers in gdb to use it.  This reduces the
amount of explicit reference counting that is done in the Python code.
I also found and fixed a latent bug in gdbpy_print_stack -- it was not
correctly checking some error conditions, nor clearing the exception
when needed.

gdb/ChangeLog
2019-01-03  Tom Tromey  <tom@tromey.com>

	* python/python.c (gdbpy_enter, ~gdbpy_enter): Update.
	(gdbpy_print_stack): Use gdbpy_err_fetch.
	* python/python-internal.h (class gdbpy_err_fetch): New class.
	(class gdbpy_enter) <m_error_type, m_error_value,
	m_error_traceback>: Remove.
	<m_error>: New member.
	(gdbpy_exception_to_string): Don't declare.
	* python/py-varobj.c (py_varobj_iter_next): Use gdbpy_err_fetch.
	* python/py-value.c (convert_value_from_python): Use
	gdbpy_err_fetch.
	* python/py-utils.c (gdbpy_err_fetch::to_string): Rename from
	gdbpy_exception_to_string.
	(gdbpy_handle_exception): Use gdbpy_err_fetch.
	* python/py-prettyprint.c (print_stack_unless_memory_error): Use
	gdbpy_err_fetch.

1 files changed, 2 insertions, 8 deletions

diff --git a/gdb/python/py-varobj.c b/gdb/python/py-varobj.c
index 38da443..274b2de 100644
--- a/gdb/python/py-varobj.c
+++ b/gdb/python/py-varobj.c
@@ -70,14 +70,8 @@ py_varobj_iter_next (struct varobj_iter *self)
       /* If we got a memory error, just use the text as the item.  */
       if (PyErr_ExceptionMatches (gdbpy_gdb_memory_error))
 	{
-	  PyObject *type, *value, *trace;
-
-	  PyErr_Fetch (&type, &value, &trace);
-	  gdb::unique_xmalloc_ptr<char>
-	    value_str (gdbpy_exception_to_string (type, value));
-	  Py_XDECREF (type);
-	  Py_XDECREF (value);
-	  Py_XDECREF (trace);
+	  gdbpy_err_fetch fetched_error;
+	  gdb::unique_xmalloc_ptr<char> value_str = fetched_error.to_string ();
 	  if (value_str == NULL)
 	    {
 	      gdbpy_print_stack ();