[PATCH 4/4] Convert frapy_richcompare to safety API

This converts frapy_richcompare to the Python safety API.  A new
wrap_richcompare template function is added.  As 'richcompare' can
return three results (or throw), the wrapped method returns a
std::optional<bool>; this is documented by the wrapper.

I considered a specialization of wrap_richcompare that automatically
ensures that the compared-to value is of the same class as 'this' --
this would be useful in a few (but not all) spots in gdb.  However
this seemed like a refinement that could easily be added later.

This also removes a part of a comment that I think is incorrect.
---
 gdb/python/py-frame.c  | 24 +++++++++++-------------
 gdb/python/py-safety.h | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+), 13 deletions(-)

diff --git a/gdb/python/py-frame.c b/gdb/python/py-frame.c
index 4dd174cf5ae..4aedd7db563 100644
--- a/gdb/python/py-frame.c
+++ b/gdb/python/py-frame.c
@@ -141,6 +141,9 @@ struct frame_object : public PyObject
   /* The static link for this frame.  */
   gdbpy_ref<> static_link ();
 
+  /* Implementation of the Python richcompare API.  */
+  std::optional<bool> richcompare (gdbpy_borrowed_ref<> other, int op);
+
   static PyTypeObject *corresponding_object_type;
 };
 
@@ -482,30 +485,25 @@ gdbpy_frame_stop_reason_string (gdbpy_borrowed_ref<> args,
   return unwind_stop_reason_to_string ((enum unwind_stop_reason) reason);
 }
 
-/* Implements the equality comparison for Frame objects.
-   All other comparison operators will throw a TypeError Python exception,
-   as they aren't valid for frames.  */
+/* Implements the equality comparison for Frame objects.  */
 
-static PyObject *
-frapy_richcompare (PyObject *self, PyObject *other, int op)
+std::optional<bool>
+frame_object::richcompare (gdbpy_borrowed_ref<> other, int op)
 {
   int result;
 
   if (!PyObject_TypeCheck (other, &frame_object_type)
       || (op != Py_EQ && op != Py_NE))
-    return py_notimplemented ().release ();
+    return std::nullopt;
 
-  frame_object *self_frame = (frame_object *) self;
-  frame_object *other_frame = (frame_object *) other;
+  frame_object *other_frame = other;
 
-  if (self_frame->frame_id == other_frame->frame_id)
+  if (frame_id == other_frame->frame_id)
     result = Py_EQ;
   else
     result = Py_NE;
 
-  if (op == result)
-    return py_true ().release ();
-  return py_false ().release ();
+  return op == result;
 }
 
 PyTypeObject *frame_object::corresponding_object_type = &frame_object_type;
@@ -623,7 +621,7 @@ PyTypeObject frame_object_type = {
   "GDB frame object",		  /* tp_doc */
   0,				  /* tp_traverse */
   0,				  /* tp_clear */
-  frapy_richcompare,		  /* tp_richcompare */
+  wrap_richcompare<frame_object, &frame_object::richcompare>, /* tp_richcompare */
   0,				  /* tp_weaklistoffset */
   0,				  /* tp_iter */
   0,				  /* tp_iternext */
diff --git a/gdb/python/py-safety.h b/gdb/python/py-safety.h
index 06324868817..e2cd8bc3f30 100644
--- a/gdb/python/py-safety.h
+++ b/gdb/python/py-safety.h
@@ -364,4 +364,36 @@ wrap_setter (PyObject *arg, PyObject *value, void *closure)
   return 0;
 }
 
+/* A function that wraps a richcompare method.
+
+   A Python tp_richcompare function can either raise an exception,
+   return True or False, or return "not implemented".  The wrapped
+   method must return a std::optional<bool>, which allows all these
+   results: exceptions are simply thrown, true and false are ordinary
+   returns, and the return of an empty optional means "not
+   implemented".  */
+template<typename C, std::optional<bool> (C::*M) (gdbpy_borrowed_ref<>, int)>
+PyObject *
+wrap_richcompare (PyObject *arg, PyObject *value, int op)
+{
+  using namespace safety_details;
+  try
+    {
+      C *self = static_cast<C *> (arg);
+      std::optional<bool> result = (self->*M) (value, op);
+      if (result.has_value ())
+	return to_python (*result);
+      return py_notimplemented ().release ();
+    }
+  catch (const gdb_python_exception &pye)
+    {
+      gdb_assert (PyErr_Occurred () != nullptr);
+      return nullptr;
+    }
+  catch (const gdb_exception &exc)
+    {
+      return gdbpy_handle_gdb_exception (nullptr, exc);
+    }
+}
+
 #endif /* GDB_PYTHON_PY_SAFETY_H */

-- 
2.49.0