unconditionally remove last character, tests

Author: johnzhou721

Lib/idlelib/editor.py

@@ -1338,23 +1338,23 @@ def set_indentation_params(self, is_py_src, guess=True):
                 self.usetabs = False
         self.set_tk_tabwidth(self.tabwidth)
 
-    def delete_trail_whitespace(self, want, chars, tabwidth):
+    def delete_trail_char_and_space(self, want, chars, tabwidth):
+        chars = chars[:-1]  # remove last character unconditionally
         current_pos = 0
         ncharsretained = 0
         for char in chars:
             if char == '\t':
                 current_pos = (current_pos // tabwidth + 1) * tabwidth
             else:
                 current_pos += 1
-            ncharsretained += 1
             if current_pos > want:
-                ncharsretained -= 1
                 break
+            ncharsretained += 1
         for i in range(ncharsretained, len(chars)):
             if chars[i] not in " \t":
                 ncharsretained = i + 1
         chars = chars[:ncharsretained]
-        return len(chars) - ncharsretained, chars
+        return len(chars) - ncharsretained + 1, chars  # removal of last
 
     def smart_backspace_event(self, event):
         text = self.text
@@ -1384,7 +1384,7 @@ def smart_backspace_event(self, event):
         assert have > 0
         want = ((have - 1) // self.indentwidth) * self.indentwidth
         # Debug prompt is multilined....
-        ncharsdeleted, chars = self.delete_trail_whitespace(want, chars, tabwidth)
+        ncharsdeleted, chars = self.delete_trail_char_and_space(want, chars, tabwidth)
         text.undo_block_start()
         text.delete("insert-%dc" % ncharsdeleted, "insert")
         if have < want:

Lib/idlelib/idle_test/test_editor.py

@@ -239,20 +239,41 @@ def test_rclick(self):
 
 class DeleteWantTest(unittest.TestCase):
 
-    def test_delete_trail_whitespace(self):
+    def test_delete_trail_char_and_space(self):
         with unittest.mock.patch.object(Editor, '__init__', return_value=None) as mock_init:
             ew = Editor()
+            
             test_str = "abcde" + 10000 * "\t" + 10000 * " "
-            res_str = ew.delete_trail_whitespace(30000, test_str, 4)[1]
+            res_str = ew.delete_trail_char_and_space(30000, test_str, 4)[1]
             self.assertEqual(res_str, "abcde" + 7499 * "\t")
-            res_str = ew.delete_trail_whitespace(41005, test_str, 4)[1]
+            res_str = ew.delete_trail_char_and_space(41005, test_str, 4)[1]
             self.assertEqual(res_str, "abcde" + 10000 * "\t" + 1001 * " ")
-            res_str = ew.delete_trail_whitespace(3, test_str, 4)[1]
+            res_str = ew.delete_trail_char_and_space(3, test_str, 4)[1]
             self.assertEqual(res_str, "abcde")
-            res_str = ew.delete_trail_whitespace(6, test_str, 4)[1]
+            res_str = ew.delete_trail_char_and_space(6, test_str, 4)[1]
             self.assertEqual(res_str, "abcde")
-            res_str = ew.delete_trail_whitespace(30002, test_str, 4)[1]
+            res_str = ew.delete_trail_char_and_space(30002, test_str, 4)[1]
             self.assertEqual(res_str, "abcde" + 7499 * "\t")
+            
+            test_str = "abcde\tabd\t\t"
+            res_str = ew.delete_trail_char_and_space(7, test_str, 4)[1]
+            self.assertEqual(res_str, "abcde\tabd")
+            res_str = ew.delete_trail_char_and_space(12, test_str, 4)[1]
+            self.assertEqual(res_str, "abcde\tabd\t")
+            res_str = ew.delete_trail_char_and_space(13, test_str, 4)[1]
+            self.assertEqual(res_str, "abcde\tabd\t")
+            res_str = ew.delete_trail_char_and_space(16, test_str, 4)[1]
+            self.assertEqual(res_str, "abcde\tabd\t")
+            
+            test_str = "abcde\tabd\t \ta"
+            res_str = ew.delete_trail_char_and_space(7, test_str, 4)[1]
+            self.assertEqual(res_str, "abcde\tabd")
+            res_str = ew.delete_trail_char_and_space(12, test_str, 4)[1]
+            self.assertEqual(res_str, "abcde\tabd\t")
+            res_str = ew.delete_trail_char_and_space(13, test_str, 4)[1]
+            self.assertEqual(res_str, "abcde\tabd\t ")
+            res_str = ew.delete_trail_char_and_space(16, test_str, 4)[1]
+            self.assertEqual(res_str, "abcde\tabd\t \t")
 
 if __name__ == '__main__':
     unittest.main(verbosity=2)