bpo-32989: IDLE - fix bad editor call of pyparse method (GH-5968)

Fix comments and add tests for editor newline_and_indent_event method.
Remove unused None default for function parameter of pyparse find_good_parse_start method
and code triggered by that default.

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>

Lib/idlelib/idle_test/test_editor.py

@@ -2,6 +2,7 @@
 
 from idlelib import editor
 import unittest
+from collections import namedtuple
 from test.support import requires
 from tkinter import Tk
 
@@ -91,5 +92,103 @@ class TestGetLineIndent(unittest.TestCase):
                 )
 
 
+class IndentAndNewlineTest(unittest.TestCase):
+
+    @classmethod
+    def setUpClass(cls):
+        requires('gui')
+        cls.root = Tk()
+        cls.root.withdraw()
+        cls.window = Editor(root=cls.root)
+        cls.window.indentwidth = 2
+        cls.window.tabwidth = 2
+
+    @classmethod
+    def tearDownClass(cls):
+        cls.window._close()
+        del cls.window
+        cls.root.update_idletasks()
+        for id in cls.root.tk.call('after', 'info'):
+            cls.root.after_cancel(id)
+        cls.root.destroy()
+        del cls.root
+
+    def insert(self, text):
+        t = self.window.text
+        t.delete('1.0', 'end')
+        t.insert('end', text)
+        # Force update for colorizer to finish.
+        t.update()
+
+    def test_indent_and_newline_event(self):
+        eq = self.assertEqual
+        w = self.window
+        text = w.text
+        get = text.get
+        nl = w.newline_and_indent_event
+
+        TestInfo = namedtuple('Tests', ['label', 'text', 'expected', 'mark'])
+
+        tests = (TestInfo('Empty line inserts with no indent.',
+                          '  \n  def __init__(self):',
+                          '\n  \n  def __init__(self):\n',
+                          '1.end'),
+                 TestInfo('Inside bracket before space, deletes space.',
+                          '  def f1(self, a, b):',
+                          '  def f1(self,\n         a, b):\n',
+                          '1.14'),
+                 TestInfo('Inside bracket after space, deletes space.',
+                          '  def f1(self, a, b):',
+                          '  def f1(self,\n         a, b):\n',
+                          '1.15'),
+                 TestInfo('Inside string with one line - no indent.',
+                          '  """Docstring."""',
+                          '  """Docstring.\n"""\n',
+                          '1.15'),
+                 TestInfo('Inside string with more than one line.',
+                          '  """Docstring.\n  Docstring Line 2"""',
+                          '  """Docstring.\n  Docstring Line 2\n  """\n',
+                          '2.18'),
+                 TestInfo('Backslash with one line.',
+                          'a =\\',
+                          'a =\\\n  \n',
+                          '1.end'),
+                 TestInfo('Backslash with more than one line.',
+                          'a =\\\n          multiline\\',
+                          'a =\\\n          multiline\\\n          \n',
+                          '2.end'),
+                 TestInfo('Block opener - indents +1 level.',
+                          '  def f1(self):\n    pass',
+                          '  def f1(self):\n    \n    pass\n',
+                          '1.end'),
+                 TestInfo('Block closer - dedents -1 level.',
+                          '  def f1(self):\n    pass',
+                          '  def f1(self):\n    pass\n  \n',
+                          '2.end'),
+                 )
+
+        w.prompt_last_line = ''
+        for test in tests:
+            with self.subTest(label=test.label):
+                self.insert(test.text)
+                text.mark_set('insert', test.mark)
+                nl(event=None)
+                eq(get('1.0', 'end'), test.expected)
+
+        # Selected text.
+        self.insert('  def f1(self, a, b):\n    return a + b')
+        text.tag_add('sel', '1.17', '1.end')
+        nl(None)
+        # Deletes selected text before adding new line.
+        eq(get('1.0', 'end'), '  def f1(self, a,\n         \n    return a + b\n')
+
+        # Preserves the whitespace in shell prompt.
+        w.prompt_last_line = '>>> '
+        self.insert('>>> \t\ta =')
+        text.mark_set('insert', '1.5')
+        nl(None)
+        eq(get('1.0', 'end'), '>>> \na =\n')
+
+
 if __name__ == '__main__':
     unittest.main(verbosity=2)