gdb/python: break more dependencies between gdbpy_initialize_* functions

In a later commit in this series I will propose removing all of the
explicit gdbpy_initialize_* calls from python.c and replace these
calls with a more generic mechanism.

One of the side effects of this generic mechanism is that the order in
which the various Python sub-systems within GDB are initialized is no
longer guaranteed.

On the whole I don't think this matters, most of the sub-systems are
independent of each other, though testing did reveal a few places
where we did have dependencies, though I don't think those
dependencies were explicitly documented in comment anywhere.

This commit is similar to the previous one, and fixes the second
dependency issue that I found.

In this case the finish_breakpoint_object_type uses the
breakpoint_object_type as its tp_base, this means that
breakpoint_object_type must have been initialized with a call to
PyType_Ready before finish_breakpoint_object_type can be initialized.

Previously we depended on the ordering of calls to
gdbpy_initialize_breakpoints and gdbpy_initialize_finishbreakpoints in
python.c.

After this commit a new function gdbpy_breakpoint_init_breakpoint_type
exists, this function ensures that breakpoint_object_type has been
initialized, and can be called from any gdbpy_initialize_* function.

I feel that this change makes the dependency explicit, which I think
is a good thing.

There should be no user visible changes after this commit.

gdb/python/py-breakpoint.c

@@ -989,6 +989,26 @@ build_bp_list (struct breakpoint *b, PyObject *list)
   return PyList_Append (list, bp) == 0;
 }
 
+/* See python-internal.h.  */
+
+bool
+gdbpy_breakpoint_init_breakpoint_type ()
+{
+  if (breakpoint_object_type.tp_new == nullptr)
+    {
+      breakpoint_object_type.tp_new = PyType_GenericNew;
+      if (PyType_Ready (&breakpoint_object_type) < 0)
+	{
+	  /* Reset tp_new back to nullptr so future calls to this function
+	     will try calling PyType_Ready again.  */
+	  breakpoint_object_type.tp_new = nullptr;
+	  return false;
+	}
+    }
+
+  return true;
+}
+
 /* Static function to return a tuple holding all breakpoints.  */
 
 PyObject *
@@ -1216,8 +1236,7 @@ gdbpy_initialize_breakpoints (void)
 {
   int i;
 
-  breakpoint_object_type.tp_new = PyType_GenericNew;
-  if (PyType_Ready (&breakpoint_object_type) < 0)
+  if (!gdbpy_breakpoint_init_breakpoint_type ())
     return -1;
 
   if (gdb_pymodule_addobject (gdb_module, "Breakpoint",

gdb/python/py-finishbreakpoint.c

@@ -403,6 +403,9 @@ bpfinishpy_handle_exit (struct inferior *inf)
 int
 gdbpy_initialize_finishbreakpoints (void)
 {
+  if (!gdbpy_breakpoint_init_breakpoint_type ())
+    return -1;
+
   if (PyType_Ready (&finish_breakpoint_object_type) < 0)
     return -1;
 

gdb/python/python-internal.h

@@ -290,6 +290,18 @@ extern PyTypeObject frame_object_type
 extern PyTypeObject thread_object_type
     CPYCHECKER_TYPE_OBJECT_FOR_TYPEDEF ("thread_object");
 
+/* Ensure that breakpoint_object_type is initialized and return true.  If
+   breakpoint_object_type can't be initialized then set a suitable Python
+   error and return false.
+
+   This function needs to be called from any gdbpy_initialize_* function
+   that wants to reference breakpoint_object_type.  After all the
+   gdbpy_initialize_* functions have been called then breakpoint_object_type
+   is guaranteed to have been initialized, and this function does not need
+   calling before referencing breakpoint_object_type.  */
+
+extern bool gdbpy_breakpoint_init_breakpoint_type ();
+
 struct gdbpy_breakpoint_object
 {
   PyObject_HEAD