File extension defaulting to txt on macOS 15

[AntoineGautier]

Description

Follow-up on closed issue: #1396
When saving a file without any extension, .txt is automatically appended. There appears to be no option to disable this behavior.
The file format does not appear to influence this behavior. For instance, saving a Dockerfile as "Dockerfile" even when the file format is set to "Dockerfile" in CotEditor results in the file being saved as "Dockerfile.txt".
In contrast, TextEdit offers a toggle to disable the automatic addition of the ".txt" extension on save. Would it be possible to implement a similar logic in CotEditor?

To Reproduce

1. Go to 'File'
2. Click on 'Save'
3. Enter a name without any extension under 'Save As': for example Untitled
4. See that the file is saved as Untitled.txt

Expected behavior

No response

CotEditor version

5.0.4

macOS version

15.1 (24B83)

Additional context

No response

[1024jp]

Thank you for the report.
It seems to occur only on macOS 15 (or any other specific conditions) since CotEditor 5.0.5 correctly adds a filename extension on macOS 14 in my environment.
Thus, this can be either a bug on macOS 15, the behavior internally changed in macOS 15, or there is some other hidden condition triggering this issue.
Let me have some more time to investigate.

[1024jp]

I recently investigated this issue again and conclude that this is due to a change on the part of the framework provided by Apple on macOS 15.
This is like an omission in the implementation of the save panel spec change in macOS 15, which is not preferred behavior and should be fixed since the file extension is correctly removed when the user removes it character-by-character.

Unfortunately, it seems there is no way to fix the current behavior by a 3rd party developer.
I'm now writing feedback to Apple so that they can fix it.

[1024jp]

Filed FB16863615.