Avoid wobbling of AutomaticScrollbar, thonny#2258

CHANGELOG.rst

@@ -12,6 +12,7 @@ Version history
 * Fix error when trying to open a file from file browser with ENTER, #1785
 * Fix support for remote Python 3 over SSH (regression introduced in one of the 4.0.0 betas), #2249
 * Support CircuitPython with micro:bit, #2251
+* Avoid wobbling of AutomaticScrollbar, helpful report by @TooLazy0x00, #2258
 
 4.0.0b2 (2022-04-09)
 ====================

thonny/ui_utils.py

@@ -970,16 +970,40 @@ class AutoScrollbar(SafeScrollbar):
     # works if you use the grid geometry manager.
 
     def __init__(self, master=None, **kw):
+        self.hide_count = 0
+        self.gridded = False
         super().__init__(master=master, **kw)
 
     def set(self, first, last):
         if float(first) <= 0.0 and float(last) >= 1.0:
-            self.grid_remove()
+            # Need to accept 1 automatic hide, otherwise even narrow files
+            # get horizontal scrollbar
+            if self.gridded and self.hide_count < 2:
+                self.grid_remove()
         elif float(first) > 0.001 or float(last) < 0.999:
             # with >0 and <1 it occasionally made scrollbar wobble back and forth
-            self.grid()
+            if not self.gridded:
+                self.grid()
         ttk.Scrollbar.set(self, first, last)
 
+    def grid(self, *args, **kwargs):
+        super().grid(*args, **kwargs)
+        self.gridded = True
+
+    def grid_configure(self, *args, **kwargs):
+        super().grid_configure(*args, **kwargs)
+        self.gridded = True
+
+    def grid_remove(self):
+        super().grid_remove()
+        self.gridded = False
+        self.hide_count += 1
+
+    def grid_forget(self):
+        super().grid_forget()
+        self.gridded = False
+        self.hide_count += 1
+
     def pack(self, **kw):
         raise tk.TclError("cannot use pack with this widget")