Issue #19198: IDLE: tab after initial whitespace should tab, not autocomplete.

Fixes problem with writing docstrings at lease twice indented.

Lib/idlelib/autocomplete.py

@@ -78,16 +78,17 @@ class AutoComplete:
         open a completion list after that (if there is more than one
         completion)
         """
-        if hasattr(event, "mc_state") and event.mc_state:
-            # A modifier was pressed along with the tab, continue as usual.
+        if hasattr(event, "mc_state") and event.mc_state or\
+                not self.text.get("insert linestart", "insert").strip():
+            # A modifier was pressed along with the tab or
+            # there is only previous whitespace on this line, so tab.
             return None
         if self.autocompletewindow and self.autocompletewindow.is_active():
             self.autocompletewindow.complete()
             return "break"
         else:
             opened = self.open_completions(False, True, True)
-            if opened:
-                return "break"
+            return "break" if opened else None
 
     def _open_completions_later(self, *args):
         self._delayed_completion_index = self.text.index("insert")

Lib/idlelib/autocomplete_w.py

@@ -240,9 +240,8 @@ class AutoCompleteWindow:
         acw.wm_geometry("+%d+%d" % (new_x, new_y))
 
     def hide_event(self, event):
-        if not self.is_active():
-            return
-        self.hide_window()
+        if self.is_active():
+            self.hide_window()
 
     def listselect_event(self, event):
         if self.is_active():

Lib/idlelib/idle_test/test_autocomplete.py

@@ -97,6 +97,11 @@ class AutoCompleteTest(unittest.TestCase):
         self.assertIsNone(autocomplete.autocomplete_event(ev))
         del ev.mc_state
 
+        # Test that tab after whitespace is ignored.
+        self.text.insert('1.0', '        """Docstring.\n    ')
+        self.assertIsNone(autocomplete.autocomplete_event(ev))
+        self.text.delete('1.0', 'end')
+
         # If autocomplete window is open, complete() method is called
         self.text.insert('1.0', 're.')
         # This must call autocomplete._make_autocomplete_window()