Undoing previous accidental commit. Sorry I forgot to git branch.

Author: rwgk

include/pybind11/detail/type_caster_base.h

@@ -493,6 +493,46 @@ PYBIND11_NOINLINE std::string error_string() {
         PyException_SetTraceback(scope.value, scope.trace);
     }
 
+#if !defined(PYPY_VERSION)
+    if (scope.trace) {
+        auto *trace = (PyTracebackObject *) scope.trace;
+
+        /* Get the deepest trace possible */
+        while (trace->tb_next) {
+            trace = trace->tb_next;
+        }
+
+        PyFrameObject *frame = trace->tb_frame;
+        Py_XINCREF(frame);
+        errorString += "\n\nAt:\n";
+        while (frame) {
+#    if PY_VERSION_HEX >= 0x030900B1
+            PyCodeObject *f_code = PyFrame_GetCode(frame);
+#    else
+            PyCodeObject *f_code = frame->f_code;
+            Py_INCREF(f_code);
+#    endif
+            int lineno = PyFrame_GetLineNumber(frame);
+            errorString += "  ";
+            errorString += handle(f_code->co_filename).cast<std::string>();
+            errorString += '(';
+            errorString += std::to_string(lineno);
+            errorString += "): ";
+            errorString += handle(f_code->co_name).cast<std::string>();
+            errorString += '\n';
+            Py_DECREF(f_code);
+#    if PY_VERSION_HEX >= 0x030900B1
+            auto *b_frame = PyFrame_GetBack(frame);
+#    else
+            auto *b_frame = frame->f_back;
+            Py_XINCREF(b_frame);
+#    endif
+            Py_DECREF(frame);
+            frame = b_frame;
+        }
+    }
+#endif
+
     return errorString;
 }