[Bug]: Possible race condition when populating upload conflict dialog on stable27 #45661

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github OR Nextcloud Community Forum (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

When uploading a folder that already exists, the frontend code iterates through all files to be uploaded and adds those that already exist to the conflict dialog. This can result in not all affected files being listed due to a race condition.

The problem is the following: The first time addConflict() is called, the dialog is created. This happens asynchronously, but this._fileexistsshown = true is set synchronously. So subsequent addConflict() calls might already add conflicts without the object being created. Basically this._fileexistsshown can be truthy before the dialog is created.

In another scenario a similar problem got fixed with commit 5dff9d8, but this was slightly easier because the loop over affected files was more accessible.

Steps to reproduce

1. Upload a folder with subfolders and files
2. Again upload the same folder
3. In some occasions, the conflict dialog only lists a subset of the files that should get overwritten

Expected behavior

Conflict dialog should list all files that get overwritten.

Nextcloud Server version

27