Fix pyreverse type hinting for class methods (#5881)

* Fix pyreverse type hinting for class methods

This commit fixes the alignment of arguments and their type annotations
in pyreverse printer output. It does so by checking for the type of the
current function rather than the name of the first argument.
This allows class methods having a non-standard first argument
(different from "self" or "cls") to be correctly serialized in class
diagrams.

* Add test for method with None args

According to astroid docs, this happens for builtin functions
implemented in C. In this case, we return an empty argument list.

1 files changed, 10 insertions, 0 deletions

diff --git a/tests/pyreverse/test_printer.py b/tests/pyreverse/test_printer.py
index 6d240c836..5406c6e83 100644
--- a/tests/pyreverse/test_printer.py
+++ b/tests/pyreverse/test_printer.py
@@ -8,6 +8,7 @@
 from typing import Type
 
 import pytest
+from astroid import nodes
 
 from pylint.pyreverse.dot_printer import DotPrinter
 from pylint.pyreverse.plantuml_printer import PlantUmlPrinter
@@ -46,6 +47,15 @@ def test_unsupported_layout(layout: Layout, printer_class: Type[Printer]):
         printer_class(title="unittest", layout=layout)
 
 
+def test_method_arguments_none():
+    func = nodes.FunctionDef()
+    args = nodes.Arguments()
+    args.args = None
+    func.postinit(args, body=None)
+    parsed_args = Printer._get_method_arguments(func)
+    assert parsed_args == []
+
+
 class TestPlantUmlPrinter:
     printer = PlantUmlPrinter(title="unittest", layout=Layout.TOP_TO_BOTTOM)