[PATCH v3 4/7] gdb/python: allow ref_ptr<T, Policy>::new_reference to accept subclasses of T

[Matthieu Longo <matthieu.longo@arm.com>]

When ref_ptr<T,Policy>::new_reference() is specialized for 'PyObject'
(i.e. gdbpy_ref<>), it currently requires the argument type to be exactly
'PyObject *'. As a result, pointers to subclasses of 'PyObject' must be
explicitly cast before being passed, making call sites unnecessarily
verbose.

This patch makes ref_ptr<T,Policy>::new_reference() a template method
that accepts both T and subclasses of T, performing the cast to 'T *'
internally when needed. This removes redundant casts at call sites
without changing behavior.
---
 gdb/python/py-block.c    | 2 +-
 gdb/python/py-inferior.c | 2 +-
 gdbsupport/gdb_ref_ptr.h | 5 ++++-
 3 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/gdb/python/py-block.c b/gdb/python/py-block.c
index 602e86c3766..d56253141f0 100644
--- a/gdb/python/py-block.c
+++ b/gdb/python/py-block.c
@@ -346,7 +346,7 @@ block_to_block_object (const struct block *block, struct objfile *objfile)
   block_object *result = (block_object *) htab_find_with_hash (table, block,
 							       hash);
   if (result != nullptr)
-    return gdbpy_ref<>::new_reference ((PyObject *) result);
+    return gdbpy_ref<>::new_reference (result);
 
   result = PyObject_New (block_object, &block_object_type);
   if (result == nullptr)
diff --git a/gdb/python/py-inferior.c b/gdb/python/py-inferior.c
index 76e3da9f620..e55360282b6 100644
--- a/gdb/python/py-inferior.c
+++ b/gdb/python/py-inferior.c
@@ -400,7 +400,7 @@ infpy_threads (PyObject *self, PyObject *args)
 
   for (const thread_map_t::value_type &entry : *inf_obj->threads)
     {
-      auto thr = gdbpy_ref<>::new_reference ((PyObject *) entry.second.get ());
+      auto thr = gdbpy_ref<>::new_reference (entry.second.get ());
       if (PyTuple_SetItem (tuple.get (), i++, thr.release ()) < 0)
 	return nullptr;
     }
diff --git a/gdbsupport/gdb_ref_ptr.h b/gdbsupport/gdb_ref_ptr.h
index 4352ab3e7c0..0eb654324c6 100644
--- a/gdbsupport/gdb_ref_ptr.h
+++ b/gdbsupport/gdb_ref_ptr.h
@@ -197,9 +197,12 @@ class ref_ptr
   }
 
   /* Acquire a new reference and return a ref_ptr that owns it.  */
-  static ref_ptr<T, Policy> new_reference (T *obj)
+  template <class TObj>
+  static ref_ptr<T, Policy> new_reference (TObj *obj)
   {
     Policy::incref (obj);
+    if constexpr (std::is_base_of<T, TObj>::value)
+      return ref_ptr<T, Policy> (static_cast<T *> (obj));
     return ref_ptr<T, Policy> (obj);
   }
 
-- 
2.53.0