IDLE: OK sometimes fails to close configdialog

[terryjreedy]

BPO	37929
Nosy	@terryjreedy, @taleinat, @miss-islington
PRs	bpo-37929: avoid Squeezer-related config dialog crashes #15452 [3.7] bpo-37929: IDLE: avoid Squeezer-related config dialog crashes (GH-15452) #15484 [3.8] bpo-37929: IDLE: avoid Squeezer-related config dialog crashes (GH-15452) #15485

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/terryjreedy'
closed_at = <Date 2019-08-25.06:25:32.367>
created_at = <Date 2019-08-23.13:27:44.808>
labels = ['3.8', 'expert-IDLE', 'type-bug', '3.7', '3.9']
title = 'IDLE: OK sometimes fails to close configdialog'
updated_at = <Date 2019-08-25.06:25:32.366>
user = 'https://github.com/terryjreedy'

bugs.python.org fields:

activity = <Date 2019-08-25.06:25:32.366>
actor = 'taleinat'
assignee = 'terry.reedy'
closed = True
closed_date = <Date 2019-08-25.06:25:32.367>
closer = 'taleinat'
components = ['IDLE']
creation = <Date 2019-08-23.13:27:44.808>
creator = 'terry.reedy'
dependencies = []
files = []
hgrepos = []
issue_num = 37929
keywords = ['patch']
message_count = 6.0
messages = ['350281', '350356', '350428', '350430', '350431', '350433']
nosy_count = 3.0
nosy_names = ['terry.reedy', 'taleinat', 'miss-islington']
pr_nums = ['15452', '15484', '15485']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue37929'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9']

[terryjreedy]

If one opens configdialog when there is no Shell and then hits OK, the dialog fails to close. The following Squeezer-related traceback appears in associated console when there is one.

Exception in Tkinter callback
Traceback (most recent call last):
  File "F:\dev\3x\lib\tkinter\__init__.py", line 1885, in __call__
    return self.func(*args)
  File "F:\dev\3x\lib\idlelib\configdialog.py", line 172, in ok
    self.apply()
  File "F:\dev\3x\lib\idlelib\configdialog.py", line 186, in apply
    self.activate_config_changes()
  File "F:\dev\3x\lib\idlelib\configdialog.py", line 240, in activate_config_changes
    klass.reload()
  File "F:\dev\3x\lib\idlelib\squeezer.py", line 222, in reload
    instance.load_font()
  File "F:\dev\3x\lib\idlelib\squeezer.py", line 318, in load_font
    Font(text, font=text.cget('font')).measure('0')
  File "F:\dev\3x\lib\idlelib\delegator.py", line 10, in __getattr__
    attr = getattr(self.delegate, name) # May raise AttributeError
AttributeError: 'NoneType' object has no attribute 'cget'

Either the squeezer instance should be destroyed and removed along with Shell or, if keeping it is intentional, it should be removed from the update list and reinstated or if not doing that is intentional, it must either check 'if text is not None' before the access or catch the attribute error after. Tal, which?

[taleinat]

See PR #59657 with a fix.

[taleinat]

New changeset d4b4c00 by Tal Einat in branch 'master':
bpo-37929: IDLE: avoid Squeezer-related config dialog crashes (GH-15452)
d4b4c00

[miss-islington]

New changeset f2b468d by Miss Islington (bot) in branch '3.7':
bpo-37929: IDLE: avoid Squeezer-related config dialog crashes (GH-15452)
f2b468d

[miss-islington]

New changeset e266d06 by Miss Islington (bot) in branch '3.8':
bpo-37929: IDLE: avoid Squeezer-related config dialog crashes (GH-15452)
e266d06

[taleinat]

Fixed.