IDLE EOL convention not set on a empty file

[rhettinger]

BPO	41378
Nosy	@rhettinger, @terryjreedy, @ambv, @serhiy-storchaka, @eamanu
Superseder	bpo-41373: IDLE: edit/save files created by Windows Explorer
Files	0001-Fix-eol_convention-when-file-does-not-exist.patch

^{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 2020-07-24.05:50:02.723>
created_at = <Date 2020-07-24.00:42:59.585>
labels = ['3.10', 'expert-IDLE', '3.8', '3.9', 'type-crash']
title = 'IDLE EOL convention not set on a empty file'
updated_at = <Date 2020-07-24.05:50:02.722>
user = 'https://github.com/rhettinger'

bugs.python.org fields:

activity = <Date 2020-07-24.05:50:02.722>
actor = 'serhiy.storchaka'
assignee = 'terry.reedy'
closed = True
closed_date = <Date 2020-07-24.05:50:02.723>
closer = 'serhiy.storchaka'
components = ['IDLE']
creation = <Date 2020-07-24.00:42:59.585>
creator = 'rhettinger'
dependencies = []
files = ['49334']
hgrepos = []
issue_num = 41378
keywords = ['patch', '3.8regression', '3.9regression']
message_count = 4.0
messages = ['374155', '374156', '374157', '374159']
nosy_count = 5.0
nosy_names = ['rhettinger', 'terry.reedy', 'lukasz.langa', 'serhiy.storchaka', 'eamanu']
pr_nums = []
priority = 'high'
resolution = 'duplicate'
stage = 'resolved'
status = 'closed'
superseder = '41373'
type = 'crash'
url = 'https://bugs.python.org/issue41378'
versions = ['Python 3.8', 'Python 3.9', 'Python 3.10']

[rhettinger]

I think this is a new bug, present in Python 3.8.5 but not present in 3.8.3.

Steps to reproduce:

* $ touch xyzpdq.py             # Creates new file, zero bytes in length
* $ python3.8 -m idlelib.idle xyzdpq.py
* Enter text:   print('hello world')
* Attempt to save the file with Cmd-S
* This seems to be unrecoverable and results
  in losing all the code that was entered.

---------------- example session ---------------

~ $ cd tmp
~/tmp $ touch qwerty.py
~/tmp $ python3.8 -m idlelib.idle qwerty.py
Exception in Tkinter callback
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/tkinter/__init__.py", line 1883, in __call__
    return self.func(*args)
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/idlelib/multicall.py", line 176, in handler
    r = l[i](event)
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/idlelib/iomenu.py", line 200, in save
    if self.writefile(self.filename):
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/idlelib/iomenu.py", line 232, in writefile
    text = self.fixnewlines()
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/idlelib/iomenu.py", line 252, in fixnewlines
    text = text.replace("\n", self.eol_convention)
TypeError: replace() argument 2 must be str, not None

[eamanu]

Hello everybody!

When a new file is loaded, the current loadfile read for the newline to set
the eol_convention. As does not exist for a empty file a None is saved and
for that reason the exception is raised

If you consider that this patch is correct I cant submit a PR

Cheers

[rhettinger]

This may have been caused by c3fa753 for https://bugs.python.org/issue41378