fix: strdup args added after initialize_generic in def_property_static (pybindgh-5976)

`def_property_static` calls `process_attributes::init` on already-initialized
function records (after `initialize_generic`'s strdup loop has run).
Args added at this stage (e.g. "self" via `append_self_arg_if_needed`) remain
as string literals, so `destruct()` would call `free()` on them.

Fix by strdup'ing name/descr of any args appended by the late
`process_attributes::init` call. Root cause introduced by pybindgh-5486.

Made-with: Cursor

Author: rwgk

include/pybind11/pybind11.h

@@ -2687,19 +2687,41 @@ class class_ : public detail::generic_type {
         if (rec_fget) {
             char *doc_prev = rec_fget->doc; /* 'extra' field may include a property-specific
                                                documentation string */
+            auto args_before = rec_fget->args.size();
             detail::process_attributes<Extra...>::init(extra..., rec_fget);
             if (rec_fget->doc && rec_fget->doc != doc_prev) {
                 std::free(doc_prev);
                 rec_fget->doc = PYBIND11_COMPAT_STRDUP(rec_fget->doc);
             }
+            // Args added by process_attributes (e.g. "self" via is_method + pos_only/kw_only)
+            // need their strings strdup'd: initialize_generic's strdup loop already ran during
+            // cpp_function construction, so it won't process these late additions. Without this,
+            // destruct() would call free() on string literals. See gh-5976.
+            for (auto i = args_before; i < rec_fget->args.size(); ++i) {
+                if (rec_fget->args[i].name) {
+                    rec_fget->args[i].name = PYBIND11_COMPAT_STRDUP(rec_fget->args[i].name);
+                }
+                if (rec_fget->args[i].descr) {
+                    rec_fget->args[i].descr = PYBIND11_COMPAT_STRDUP(rec_fget->args[i].descr);
+                }
+            }
         }
         if (rec_fset) {
             char *doc_prev = rec_fset->doc;
+            auto args_before = rec_fset->args.size();
             detail::process_attributes<Extra...>::init(extra..., rec_fset);
             if (rec_fset->doc && rec_fset->doc != doc_prev) {
                 std::free(doc_prev);
                 rec_fset->doc = PYBIND11_COMPAT_STRDUP(rec_fset->doc);
             }
+            for (auto i = args_before; i < rec_fset->args.size(); ++i) {
+                if (rec_fset->args[i].name) {
+                    rec_fset->args[i].name = PYBIND11_COMPAT_STRDUP(rec_fset->args[i].name);
+                }
+                if (rec_fset->args[i].descr) {
+                    rec_fset->args[i].descr = PYBIND11_COMPAT_STRDUP(rec_fset->args[i].descr);
+                }
+            }
             if (!rec_active) {
                 rec_active = rec_fset;
             }