Use shared_ptr custom deleter for m_fetched_error in error_already_set. This enables removing the dtor, copy ctor, move ctor completely.

Author: rwgk

include/pybind11/pybind11.h

@@ -2625,13 +2625,12 @@ void print(Args &&...args) {
     detail::print(c.args(), c.kwargs());
 }
 
-inline error_already_set::~error_already_set() {
-    if (m_fetched_error.use_count() != 1 || !m_fetched_error->has_py_object_references()) {
-        return; // Avoid gil and scope overhead if there is nothing to release.
-    }
+inline void
+error_already_set::m_fetched_error_deleter(detail::error_fetch_and_normalize *raw_ptr) {
     gil_scoped_acquire gil;
     error_scope scope;
-    m_fetched_error->release_py_object_references();
+    raw_ptr->release_py_object_references();
+    delete raw_ptr;
 }
 
 inline const char *error_already_set::what() const noexcept {

include/pybind11/pytypes.h

@@ -541,8 +541,6 @@ struct error_fetch_and_normalize {
         return (PyErr_GivenExceptionMatches(m_type.ptr(), exc.ptr()) != 0);
     }
 
-    bool has_py_object_references() const { return m_type || m_value || m_trace; }
-
     void release_py_object_references() {
         m_type.release().dec_ref();
         m_value.release().dec_ref();
@@ -580,20 +578,8 @@ class PYBIND11_EXPORT_EXCEPTION error_already_set : public std::exception {
     /// Fetches the current Python exception (using PyErr_Fetch()), which will clear the
     /// current Python error indicator.
     error_already_set()
-        : m_fetched_error{
-            std::make_shared<detail::error_fetch_and_normalize>("pybind11::error_already_set")} {}
-
-    /// WARNING: This destructor needs to acquire the Python GIL. This can lead to
-    ///          crashes (undefined behavior) if the Python interpreter is finalizing.
-    ~error_already_set() override;
-
-    // This copy ctor does not need the GIL because it simply increments a shared_ptr use_count.
-    error_already_set(const error_already_set &) noexcept = default;
-
-    // This move ctor cannot easily be deleted (some compilers need it).
-    // It is the responsibility of the caller to not use the moved-from object.
-    // For simplicity, guarding ifs are omitted.
-    error_already_set(error_already_set &&) noexcept = default;
+        : m_fetched_error{new detail::error_fetch_and_normalize("pybind11::error_already_set"),
+                          m_fetched_error_deleter} {}
 
     /// The what() result is built lazily on demand.
     /// WARNING: This member function needs to acquire the Python GIL. This can lead to
@@ -637,6 +623,10 @@ class PYBIND11_EXPORT_EXCEPTION error_already_set : public std::exception {
 
 private:
     std::shared_ptr<detail::error_fetch_and_normalize> m_fetched_error;
+
+    /// WARNING: This custom deleter needs to acquire the Python GIL. This can lead to
+    ///          crashes (undefined behavior) if the Python interpreter is finalizing.
+    static void m_fetched_error_deleter(detail::error_fetch_and_normalize *raw_ptr);
 };
 #if defined(_MSC_VER)
 #    pragma warning(pop)