bpo-37929: IDLE: avoid Squeezer-related config dialog crashes (GH-15452)

These were caused by keeping around a reference to the Squeezer
instance and calling it's load_font() upon config changes, which
sometimes happened even if the shell window no longer existed.

This change completely removes that mechanism, instead having the
editor window properly update its width attribute, which can then
be used by Squeezer.

Lib/idlelib/squeezer.py

@@ -15,10 +15,8 @@
 messages and their tracebacks.
 """
 import re
-import weakref
 
 import tkinter as tk
-from tkinter.font import Font
 import tkinter.messagebox as tkMessageBox
 
 from idlelib.config import idleConf
@@ -203,8 +201,6 @@ class Squeezer:
     This avoids IDLE's shell slowing down considerably, and even becoming
     completely unresponsive, when very long outputs are written.
     """
-    _instance_weakref = None
-
     @classmethod
     def reload(cls):
         """Load class variables from config."""
@@ -213,14 +209,6 @@ def reload(cls):
             type="int", default=50,
         )
 
-        # Loading the font info requires a Tk root. IDLE doesn't rely
-        # on Tkinter's "default root", so the instance will reload
-        # font info using its editor windows's Tk root.
-        if cls._instance_weakref is not None:
-            instance = cls._instance_weakref()
-            if instance is not None:
-                instance.load_font()
-
     def __init__(self, editwin):
         """Initialize settings for Squeezer.
 
@@ -241,9 +229,6 @@ def __init__(self, editwin):
         # however, needs to make such changes.
         self.base_text = editwin.per.bottom
 
-        Squeezer._instance_weakref = weakref.ref(self)
-        self.load_font()
-
         # Twice the text widget's border width and internal padding;
         # pre-calculated here for the get_line_width() method.
         self.window_width_delta = 2 * (
@@ -298,24 +283,7 @@ def count_lines(self, s):
 
         Tabs are considered tabwidth characters long.
         """
-        linewidth = self.get_line_width()
-        return count_lines_with_wrapping(s, linewidth)
-
-    def get_line_width(self):
-        # The maximum line length in pixels: The width of the text
-        # widget, minus twice the border width and internal padding.
-        linewidth_pixels = \
-            self.base_text.winfo_width() - self.window_width_delta
-
-        # Divide the width of the Text widget by the font width,
-        # which is taken to be the width of '0' (zero).
-        # http://www.tcl.tk/man/tcl8.6/TkCmd/text.htm#M21
-        return linewidth_pixels // self.zero_char_width
-
-    def load_font(self):
-        text = self.base_text
-        self.zero_char_width = \
-            Font(text, font=text.cget('font')).measure('0')
+        return count_lines_with_wrapping(s, self.editwin.width)
 
     def squeeze_current_text_event(self, event):
         """squeeze-current-text event handler