bpo-30579: Allow TracebackType creation and tb_next mutation from Python (GH-4793)

Third party projects may wish to hide their own internal machinery in
order to present more comprehensible tracebacks to end users
(e.g. Jinja2 and Trio both do this).

Previously such projects have had to rely on ctypes to do so:

  https://github.com/pallets/jinja/blob/fe3dadacdf4cf411d0a5b6bbd4d5234697a28af2/jinja2/debug.py#L345
  https://github.com/python-trio/trio/blob/1e86b1aee8c0c759f6f239ae53a05d0d3963c629/trio/_core/_multierror.py#L296

This provides a Python level API for creating and modifying real
Traceback objects, allowing tracebacks to be edited at runtime.

Patch by Nathaniel Smith.

1 files changed, 35 insertions, 0 deletions

diff --git a/Python/clinic/traceback.c.h b/Python/clinic/traceback.c.h
new file mode 100644
index 0000000..d9daccb
--- /dev/null
+++ b/Python/clinic/traceback.c.h
@@ -0,0 +1,35 @@
+/*[clinic input]
+preserve
+[clinic start generated code]*/
+
+PyDoc_STRVAR(tb_new__doc__,
+"TracebackType(tb_next, tb_frame, tb_lasti, tb_lineno)\n"
+"--\n"
+"\n"
+"Create a new traceback object.");
+
+static PyObject *
+tb_new_impl(PyTypeObject *type, PyObject *tb_next, PyFrameObject *tb_frame,
+            int tb_lasti, int tb_lineno);
+
+static PyObject *
+tb_new(PyTypeObject *type, PyObject *args, PyObject *kwargs)
+{
+    PyObject *return_value = NULL;
+    static const char * const _keywords[] = {"tb_next", "tb_frame", "tb_lasti", "tb_lineno", NULL};
+    static _PyArg_Parser _parser = {"OO!ii:TracebackType", _keywords, 0};
+    PyObject *tb_next;
+    PyFrameObject *tb_frame;
+    int tb_lasti;
+    int tb_lineno;
+
+    if (!_PyArg_ParseTupleAndKeywordsFast(args, kwargs, &_parser,
+        &tb_next, &PyFrame_Type, &tb_frame, &tb_lasti, &tb_lineno)) {
+        goto exit;
+    }
+    return_value = tb_new_impl(type, tb_next, tb_frame, tb_lasti, tb_lineno);
+
+exit:
+    return return_value;
+}
+/*[clinic end generated code: output=0133130d7d19556f input=a9049054013a1b77]*/