Support using handle for absl::Cord saving a memcpy.

PiperOrigin-RevId: 730367644

Author: charlesbeattie

pybind11_abseil/absl_casters.h

@@ -32,6 +32,7 @@
 #ifndef PYBIND11_ABSEIL_ABSL_CASTERS_H_
 #define PYBIND11_ABSEIL_ABSL_CASTERS_H_
 
+#include <Python.h>
 #include <pybind11/cast.h>
 #include <pybind11/pybind11.h>
 #include <pybind11/stl.h>
@@ -43,8 +44,10 @@
 #include <complex>
 #include <cstdint>
 #include <cstring>
+#include <optional>
 #include <tuple>
 #include <type_traits>
+#include <utility>
 #include <vector>
 
 #include "absl/cleanup/cleanup.h"
@@ -618,10 +621,39 @@ struct type_caster<absl::Cord> {
 
   // Conversion part 1 (Python->C++)
   bool load(handle src, bool convert) {
+    // If the source is a bytes/string object, we can avoid a copy by using
+    // absl::MakeCordFromExternal.
+    std::optional<absl::string_view> view;
+    if (PyUnicode_Check(src.ptr())) {
+      Py_ssize_t size = 0;
+      const char* data = PyUnicode_AsUTF8AndSize(src.ptr(), &size);
+      if (data) {
+        view = absl::string_view(data, size);
+      } else {
+        PyErr_Clear();
+      }
+    } else if (PyBytes_Check(src.ptr())) {
+      view = absl::string_view(PyBytes_AS_STRING(src.ptr()),
+                               PyBytes_GET_SIZE(src.ptr()));
+    }
+    if (view.has_value()) {
+      if (!view->empty()) {
+        // Bypass StringViewCaster life support as absl::Cord may outlive the
+        // handle.
+        src.inc_ref();
+        value = absl::MakeCordFromExternal(*view, [src] {
+          PyGILState_STATE gstate = PyGILState_Ensure();
+          src.dec_ref();
+          PyGILState_Release(gstate);
+        });
+      } else {
+        value.Clear();
+      }
+      return true;
+    }
     auto caster = StringViewCaster();
     if (caster.load(src, convert)) {
-      absl::string_view view = cast_op<absl::string_view>(std::move(caster));
-      value = view;
+      value = absl::Cord(cast_op<absl::string_view>(std::move(caster)));
       return true;
     }
     return false;