gh-116022: Improve repr() of AST nodes (#117046)

Co-authored-by: AN Long <aisk@users.noreply.github.com>
Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

Python/Python-ast.c

@@ -5636,8 +5636,230 @@ static PyGetSetDef ast_type_getsets[] = {
     {NULL}
 };
 
+static PyObject *
+ast_repr_max_depth(AST_object *self, int depth);
+
+/* Format list and tuple properties of AST nodes.
+   Note that, only the first and last elements are shown.
+   Anything in between is represented with an ellipsis ('...').
+   For example, the list [1, 2, 3] is formatted as
+   'List(elts=[Constant(1), ..., Constant(3)])'. */
+static PyObject *
+ast_repr_list(PyObject *list, int depth)
+{
+    assert(PyList_Check(list) || PyTuple_Check(list));
+
+    struct ast_state *state = get_ast_state();
+    if (state == NULL) {
+        return NULL;
+    }
+
+    Py_ssize_t length = PySequence_Size(list);
+    if (length < 0) {
+        return NULL;
+    }
+    else if (length == 0) {
+        return PyObject_Repr(list);
+    }
+
+    _PyUnicodeWriter writer;
+    _PyUnicodeWriter_Init(&writer);
+    writer.overallocate = 1;
+    PyObject *items[2] = {NULL, NULL};
+
+    items[0] = PySequence_GetItem(list, 0);
+    if (!items[0]) {
+        goto error;
+    }
+    if (length > 1) {
+        items[1] = PySequence_GetItem(list, length - 1);
+        if (!items[1]) {
+            goto error;
+        }
+    }
+
+    bool is_list = PyList_Check(list);
+    if (_PyUnicodeWriter_WriteChar(&writer, is_list ? '[' : '(') < 0) {
+        goto error;
+    }
+
+    for (Py_ssize_t i = 0; i < Py_MIN(length, 2); i++) {
+        PyObject *item = items[i];
+        PyObject *item_repr;
+
+        if (PyType_IsSubtype(Py_TYPE(item), (PyTypeObject *)state->AST_type)) {
+            item_repr = ast_repr_max_depth((AST_object*)item, depth - 1);
+        } else {
+            item_repr = PyObject_Repr(item);
+        }
+        if (!item_repr) {
+            goto error;
+        }
+        if (i > 0) {
+            if (_PyUnicodeWriter_WriteASCIIString(&writer, ", ", 2) < 0) {
+                goto error;
+            }
+        }
+        if (_PyUnicodeWriter_WriteStr(&writer, item_repr) < 0) {
+            Py_DECREF(item_repr);
+            goto error;
+        }
+        if (i == 0 && length > 2) {
+            if (_PyUnicodeWriter_WriteASCIIString(&writer, ", ...", 5) < 0) {
+                Py_DECREF(item_repr);
+                goto error;
+            }
+        }
+        Py_DECREF(item_repr);
+    }
+
+    if (_PyUnicodeWriter_WriteChar(&writer, is_list ? ']' : ')') < 0) {
+        goto error;
+    }
+
+    Py_XDECREF(items[0]);
+    Py_XDECREF(items[1]);
+    return _PyUnicodeWriter_Finish(&writer);
+
+error:
+    Py_XDECREF(items[0]);
+    Py_XDECREF(items[1]);
+    _PyUnicodeWriter_Dealloc(&writer);
+    return NULL;
+}
+
+static PyObject *
+ast_repr_max_depth(AST_object *self, int depth)
+{
+    struct ast_state *state = get_ast_state();
+    if (state == NULL) {
+        return NULL;
+    }
+
+    if (depth <= 0) {
+        return PyUnicode_FromFormat("%s(...)", Py_TYPE(self)->tp_name);
+    }
+
+    int status = Py_ReprEnter((PyObject *)self);
+    if (status != 0) {
+        if (status < 0) {
+            return NULL;
+        }
+        return PyUnicode_FromFormat("%s(...)", Py_TYPE(self)->tp_name);
+    }
+
+    PyObject *fields;
+    if (PyObject_GetOptionalAttr((PyObject *)Py_TYPE(self), state->_fields, &fields) < 0) {
+        Py_ReprLeave((PyObject *)self);
+        return NULL;
+    }
+
+    Py_ssize_t numfields = PySequence_Size(fields);
+    if (numfields < 0) {
+        Py_ReprLeave((PyObject *)self);
+        Py_DECREF(fields);
+        return NULL;
+    }
+
+    if (numfields == 0) {
+        Py_ReprLeave((PyObject *)self);
+        Py_DECREF(fields);
+        return PyUnicode_FromFormat("%s()", Py_TYPE(self)->tp_name);
+    }
+
+    const char* tp_name = Py_TYPE(self)->tp_name;
+    _PyUnicodeWriter writer;
+    _PyUnicodeWriter_Init(&writer);
+    writer.overallocate = 1;
+
+    if (_PyUnicodeWriter_WriteASCIIString(&writer, tp_name, strlen(tp_name)) < 0) {
+        goto error;
+    }
+    if (_PyUnicodeWriter_WriteChar(&writer, '(') < 0) {
+        goto error;
+    }
+
+    for (Py_ssize_t i = 0; i < numfields; i++) {
+        PyObject *name = PySequence_GetItem(fields, i);
+        if (!name) {
+            goto error;
+        }
+
+        PyObject *value = PyObject_GetAttr((PyObject *)self, name);
+        if (!value) {
+            Py_DECREF(name);
+            goto error;
+        }
+
+        PyObject *value_repr;
+        if (PyList_Check(value) || PyTuple_Check(value)) {
+            value_repr = ast_repr_list(value, depth);
+        }
+        else if (PyType_IsSubtype(Py_TYPE(value), (PyTypeObject *)state->AST_type)) {
+            value_repr = ast_repr_max_depth((AST_object*)value, depth - 1);
+        }
+        else {
+            value_repr = PyObject_Repr(value);
+        }
+
+        Py_DECREF(value);
+
+        if (!value_repr) {
+            Py_DECREF(name);
+            Py_DECREF(value);
+            goto error;
+        }
+
+        if (i > 0) {
+            if (_PyUnicodeWriter_WriteASCIIString(&writer, ", ", 2) < 0) {
+                Py_DECREF(name);
+                Py_DECREF(value_repr);
+                goto error;
+            }
+        }
+        if (_PyUnicodeWriter_WriteStr(&writer, name) < 0) {
+            Py_DECREF(name);
+            Py_DECREF(value_repr);
+            goto error;
+        }
+
+        Py_DECREF(name);
+
+        if (_PyUnicodeWriter_WriteChar(&writer, '=') < 0) {
+            Py_DECREF(value_repr);
+            goto error;
+        }
+        if (_PyUnicodeWriter_WriteStr(&writer, value_repr) < 0) {
+            Py_DECREF(value_repr);
+            goto error;
+        }
+
+        Py_DECREF(value_repr);
+    }
+
+    if (_PyUnicodeWriter_WriteChar(&writer, ')') < 0) {
+        goto error;
+    }
+    Py_ReprLeave((PyObject *)self);
+    Py_DECREF(fields);
+    return _PyUnicodeWriter_Finish(&writer);
+
+error:
+    Py_ReprLeave((PyObject *)self);
+    Py_DECREF(fields);
+    _PyUnicodeWriter_Dealloc(&writer);
+    return NULL;
+}
+
+static PyObject *
+ast_repr(AST_object *self)
+{
+    return ast_repr_max_depth(self, 3);
+}
+
 static PyType_Slot AST_type_slots[] = {
     {Py_tp_dealloc, ast_dealloc},
+    {Py_tp_repr, ast_repr},
     {Py_tp_getattro, PyObject_GenericGetAttr},
     {Py_tp_setattro, PyObject_GenericSetAttr},
     {Py_tp_traverse, ast_traverse},