Added py::args ref counting tests

tests/test_kwargs_and_defaults.cpp

@@ -8,6 +8,7 @@
 */
 
 #include "pybind11_tests.h"
+#include "constructor_stats.h"
 #include <pybind11/stl.h>
 
 TEST_SUBMODULE(kwargs_and_defaults, m) {
@@ -53,6 +54,34 @@ TEST_SUBMODULE(kwargs_and_defaults, m) {
     m.def("mixed_plus_args_kwargs_defaults", mixed_plus_both,
             py::arg("i") = 1, py::arg("j") = 3.14159);
 
+    // test_args_refcount
+    // PyPy needs a garbage collection to get the reference count values to match CPython's behaviour
+    #ifdef PYPY_VERSION
+    #define GC_IF_NEEDED ConstructorStats::gc()
+    #else
+    #define GC_IF_NEEDED
+    #endif
+    m.def("arg_refcount_h", [](py::handle h) { GC_IF_NEEDED; return h.ref_count(); });
+    m.def("arg_refcount_h", [](py::handle h, py::handle, py::handle) { GC_IF_NEEDED; return h.ref_count(); });
+    m.def("arg_refcount_o", [](py::object o) { GC_IF_NEEDED; return o.ref_count(); });
+    m.def("args_refcount", [](py::args a) {
+        GC_IF_NEEDED;
+        py::tuple t(a.size());
+        for (size_t i = 0; i < a.size(); i++)
+            // Use raw Python API here to avoid an extra, intermediate incref on the tuple item:
+            t[i] = (int) Py_REFCNT(PyTuple_GET_ITEM(a.ptr(), static_cast<ssize_t>(i)));
+        return t;
+    });
+    m.def("mixed_args_refcount", [](py::object o, py::args a) {
+        GC_IF_NEEDED;
+        py::tuple t(a.size() + 1);
+        t[0] = o.ref_count();
+        for (size_t i = 0; i < a.size(); i++)
+            // Use raw Python API here to avoid an extra, intermediate incref on the tuple item:
+            t[i + 1] = (int) Py_REFCNT(PyTuple_GET_ITEM(a.ptr(), static_cast<ssize_t>(i)));
+        return t;
+    });
+
     // pybind11 won't allow these to be bound: args and kwargs, if present, must be at the end.
     // Uncomment these to test that the static_assert is indeed working:
 //    m.def("bad_args1", [](py::args, int) {});

tests/test_kwargs_and_defaults.py

@@ -105,3 +105,43 @@ def test_mixed_args_and_kwargs(msg):
 
         Invoked with: 1, 2; kwargs: j=1
     """  # noqa: E501 line too long
+
+
+def test_args_refcount():
+    """Issue/PR #1216 - py::args elements get double-inc_ref()ed when combined with regular
+    arguments"""
+    refcount = m.arg_refcount_h
+
+    myval = 54321
+    expected = refcount(myval)
+    assert m.arg_refcount_h(myval) == expected
+    assert m.arg_refcount_o(myval) == expected + 1
+    assert m.arg_refcount_h(myval) == expected
+    assert refcount(myval) == expected
+
+    assert m.mixed_plus_args(1, 2.0, "a", myval) == (1, 2.0, ("a", myval))
+    assert refcount(myval) == expected
+
+    assert m.mixed_plus_kwargs(3, 4.0, a=1, b=myval) == (3, 4.0, {"a": 1, "b": myval})
+    assert refcount(myval) == expected
+
+    assert m.args_function(-1, myval) == (-1, myval)
+    assert refcount(myval) == expected
+
+    assert m.mixed_plus_args_kwargs(5, 6.0, myval, a=myval) == (5, 6.0, (myval,), {"a": myval})
+    assert refcount(myval) == expected
+
+    assert m.args_kwargs_function(7, 8, myval, a=1, b=myval) == \
+        ((7, 8, myval), {"a": 1, "b": myval})
+    assert refcount(myval) == expected
+
+    exp3 = refcount(myval, myval, myval)
+    assert m.args_refcount(myval, myval, myval) == (exp3, exp3, exp3)
+    assert refcount(myval) == expected
+
+    # This function takes the first arg as a `py::object` and the rest as a `py::args`.  Unlike the
+    # previous case, when we have both positional and `py::args` we need to construct a new tuple
+    # for the `py::args`; in the previous case, we could simply inc_ref and pass on Python's input
+    # tuple without having to inc_ref the individual elements, but here we can't, hence the extra
+    # refs.
+    assert m.mixed_args_refcount(myval, myval, myval) == (exp3 + 3, exp3 + 3, exp3 + 3)