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.
(cherry picked from commit d4b4c00b57)

Co-authored-by: Tal Einat <taleinat+github@gmail.com>

Lib/idlelib/editor.py

@@ -10,6 +10,7 @@ import traceback
 import webbrowser
 
 from tkinter import *
+from tkinter.font import Font
 from tkinter.ttk import Scrollbar
 import tkinter.simpledialog as tkSimpleDialog
 import tkinter.messagebox as tkMessageBox
@@ -120,14 +121,13 @@ class EditorWindow(object):
         self.prompt_last_line = ''  # Override in PyShell
         self.text_frame = text_frame = Frame(top)
         self.vbar = vbar = Scrollbar(text_frame, name='vbar')
-        self.width = idleConf.GetOption('main', 'EditorWindow',
-                                        'width', type='int')
+        width = idleConf.GetOption('main', 'EditorWindow', 'width', type='int')
         text_options = {
                 'name': 'text',
                 'padx': 5,
                 'wrap': 'none',
                 'highlightthickness': 0,
-                'width': self.width,
+                'width': width,
                 'tabstyle': 'wordprocessor',  # new in 8.5
                 'height': idleConf.GetOption(
                         'main', 'EditorWindow', 'height', type='int'),
@@ -154,6 +154,7 @@ class EditorWindow(object):
         text.bind('<MouseWheel>', self.mousescroll)
         text.bind('<Button-4>', self.mousescroll)
         text.bind('<Button-5>', self.mousescroll)
+        text.bind('<Configure>', self.handle_winconfig)
         text.bind("<<cut>>", self.cut)
         text.bind("<<copy>>", self.copy)
         text.bind("<<paste>>", self.paste)
@@ -211,6 +212,7 @@ class EditorWindow(object):
         text['font'] = idleConf.GetFont(self.root, 'main', 'EditorWindow')
         text.grid(row=1, column=1, sticky=NSEW)
         text.focus_set()
+        self.set_width()
 
         # usetabs true  -> literal tab characters are used by indent and
         #                  dedent cmds, possibly mixed with spaces if
@@ -338,6 +340,22 @@ class EditorWindow(object):
         else:
             self.update_menu_state('options', '*Line Numbers', 'disabled')
 
+    def handle_winconfig(self, event=None):
+        self.set_width()
+
+    def set_width(self):
+        text = self.text
+        inner_padding = sum(map(text.tk.getint, [text.cget('border'),
+                                                 text.cget('padx')]))
+        pixel_width = text.winfo_width() - 2 * inner_padding
+
+        # 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
+        zero_char_width = \
+            Font(text, font=text.cget('font')).measure('0')
+        self.width = pixel_width // zero_char_width
+
     def _filename_to_unicode(self, filename):
         """Return filename as BMP unicode so displayable in Tk."""
         # Decode bytes to unicode.
@@ -830,6 +848,7 @@ class EditorWindow(object):
         # Finally, update the main text widget.
         new_font = idleConf.GetFont(self.root, 'main', 'EditorWindow')
         self.text['font'] = new_font
+        self.set_width()
 
     def RemoveKeybindings(self):
         "Remove the keybindings before they are changed."