static allocation for PyModuleDef, to avoid leak check errors.

Trying a different approach to pybind#2019.

EXPERIMENTAL, PROOF OF CONCEPT, please do not review.
If this approach works out additional work is needed to avoid code duplication.

Author: rwgk

include/pybind11/detail/common.h

@@ -306,6 +306,22 @@ extern "C" {
             });
         }
 \endrst */
+#if PY_MAJOR_VERSION >= 3
+#define PYBIND11_MODULE(name, variable)                                        \
+    PYBIND11_MAYBE_UNUSED                                                      \
+    static void PYBIND11_CONCAT(pybind11_init_, name)(pybind11::module &);     \
+    PYBIND11_PLUGIN_IMPL(name) {                                               \
+        PYBIND11_CHECK_PYTHON_VERSION                                          \
+        PYBIND11_ENSURE_INTERNALS_READY                                        \
+        static PyModuleDef mdef;                                               \
+        auto m = pybind11::module(PYBIND11_TOSTRING(name), nullptr, &mdef);    \
+        try {                                                                  \
+            PYBIND11_CONCAT(pybind11_init_, name)(m);                          \
+            return m.ptr();                                                    \
+        } PYBIND11_CATCH_INIT_EXCEPTIONS                                       \
+    }                                                                          \
+    void PYBIND11_CONCAT(pybind11_init_, name)(pybind11::module &variable)
+#else
 #define PYBIND11_MODULE(name, variable)                                        \
     PYBIND11_MAYBE_UNUSED                                                      \
     static void PYBIND11_CONCAT(pybind11_init_, name)(pybind11::module &);     \
@@ -319,6 +335,7 @@ extern "C" {
         } PYBIND11_CATCH_INIT_EXCEPTIONS                                       \
     }                                                                          \
     void PYBIND11_CONCAT(pybind11_init_, name)(pybind11::module &variable)
+#endif
 
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)

include/pybind11/pybind11.h

@@ -827,10 +827,14 @@ class module : public object {
     PYBIND11_OBJECT_DEFAULT(module, object, PyModule_Check)
 
     /// Create a new top-level Python module with the given name and docstring
+#if PY_MAJOR_VERSION >= 3
+    explicit module(const char *name, const char *doc = nullptr, PyModuleDef *def = nullptr) {
+#else
     explicit module(const char *name, const char *doc = nullptr) {
+#endif
         if (!options::show_user_defined_docstrings()) doc = nullptr;
 #if PY_MAJOR_VERSION >= 3
-        PyModuleDef *def = new PyModuleDef();
+        if (!def) def = new PyModuleDef();
         std::memset(def, 0, sizeof(PyModuleDef));
         def->m_name = name;
         def->m_doc = doc;