[PATCH v2 1/2] [gdb/python] Introduce py_none/py_true/py_false functions

[Tom de Vries <tdevries@suse.de>]

I came across this code:
...
   if (c)
     return v;
   else
     Py_RETURN_NONE;
...
and realized I couldn't easily rewrite it into "return c ? v : ...".

Probably something like this would work:
...
  return c ? v : ([] { Py_RETURN_NONE; } ());
...
but it made me wonder if we can rid of Py_RETURN_NONE.

The only point of it seems to be to increase the reference count on the
Py_None object for older python versions.

Add a refcount-safe wrapper py_none (returning a gdbpy_ref), with the aim of
replacing all uses of Py_RETURN_NONE with "return py_none ().release ()".

Likewise for Py_RETURN_TRUE/Py_RETURN_FALSE.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=34145
---
 gdb/python/python-internal.h | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/gdb/python/python-internal.h b/gdb/python/python-internal.h
index 37bc37691fe..c3c1f0e6a6f 100644
--- a/gdb/python/python-internal.h
+++ b/gdb/python/python-internal.h
@@ -1340,4 +1340,27 @@ class gdbpy_memoizing_registry_storage
 extern int eval_python_command (const char *command, int start_symbol,
 				const char *filename = nullptr);
 
+/* The following three functions are refcount-safe wrappers around
+   Py_RETURN_{NONE,TRUE,FALSE}.  Starting with python 3.12, None, True and
+   False are immortal, and increasing and decreasing refcount for such object
+   is a no-op, but while supporting older versions we ignore that aspect
+   here.  */
+
+static inline gdbpy_ref<>
+py_none ()
+{
+  return gdbpy_ref<> ([] { Py_RETURN_NONE; } ());
+}
+
+static inline gdbpy_ref<>
+py_true ()
+{
+  return gdbpy_ref<> ([] { Py_RETURN_TRUE; } ());
+}
+
+static inline gdbpy_ref<>
+py_false ()
+{
+  return gdbpy_ref<> ([] { Py_RETURN_FALSE; } ());
+}
 #endif /* GDB_PYTHON_PYTHON_INTERNAL_H */
-- 
2.51.0