bpo-41373: IDLE: Fix saving files loaded with no newlines or mixed newlines

[serhiy-storchaka]

https://bugs.python.org/issue41373

[terryjreedy]

I would like to make two changes other than the one in the comment below.

1. Line 140 'Will utf-8 decode'. Replace with encoding might be unknown rather than wrong.

2. UnicodeDecodeError on 152 can now only come from the 2nd read in 144-9.

Add to this PR? Separate PR for this issue? Separate issue?

[terryjreedy]

line 124 above is identical, except it sets eol_convention as a class attribute. The class attribute is used in fixnewlines (the only usage) for new files created in IDLE. Rather than duplicate the default, I would rather only set the instance attribute when it might not be the default.

if isinstance(eol_convention, str):
    self.eol_convention = eol_convention  # Line 172 below.
else:
    # If .... None.
    # If ... tuple.
    if eol_convention is not None:
        # Message box as below.

[serhiy-storchaka]

When you call loadfile() for the same edit window second time, eol_convention will be set to the EOL convention in previously opened file,

[terryjreedy]

At present, I don't think loadfile() is ever called more than once for an edit window*. Which means that the later line deleting current content is a no-op. But I would like to add a 'reload' function, such an when one want to restart editing, or a file is changed externally. So I agree with leaving loadfile as is, ready for such an addition.

*Except in the htest for iomenu, and I want that to continue to work.

However, the line changing eol_convention from None/tuple to string must be moved after the test for it being tuple (not None). As it is, editing a blank file brings up a spurious mixed endings message. I will change this and add a blurb.

[serhiy-storchaka]

Good catch!

AFAIK loadfile() is called for the same edit window when you pick a recent file from menu.

[terryjreedy]

Recent files not already being edited are loaded in a new window, leaving current windows alone. Asking for a file already loaded switches to its window. What I would like to add is a popup offering to discard changes and reload.

[bedevere-bot]

When you're done making the requested changes, leave the comment: I have made the requested changes; please review again.

[serhiy-storchaka]

Add to this PR? Separate PR for this issue? Separate issue?

I did not fully understand you, but I think it is a separate issue.

[eamanu]

LGTM

[terryjreedy]

I will leave other changes to another issue after adding tests in a followup PR. I tested this change after the line was moved by loading and saving both a blank file and one with different endings, and reloading the result of the latter and checking that it only had default endings. I added blurb and will merge when CI done.

[miss-islington]

Thanks @serhiy-storchaka for the PR, and @terryjreedy for merging it 🌮🎉.. I'm working now to backport this PR to: 3.8, 3.9.
🐍🍒⛏🤖

[bedevere-bot]

GH-21610 is a backport of this pull request to the 3.9 branch.

[bedevere-bot]

GH-21611 is a backport of this pull request to the 3.8 branch.

[serhiy-storchaka]

Thank you for adding blurb Terry.