Scaffold Append Fails When Appended File Is Empty File

I can only confirm the issue as it happened to me as well.

OK. So, I have been able to recreate this issue. It seems that when you empty the file assets/my-robots-additions.txt file completely (no spaces, no new lines) then it is treated as if no change was made to the file.

The problem is with drupal/core-composer-scaffold. It is successful detecting all changes to scaffolding files except when it is completely empty.

Adding needs test.

Also, I would like to help with this one so I will assign to me for now.

I'm not sure if the component "composer" is appropriate. I checked recent commits on this project and they have been either "base system" or "other".

I confirm this is also an issue with standard file mappings:

    "extra": {
        "drupal-scaffold": {
            "file-mapping": {
                "[web-root]/robots.txt": "assets/my-robots-complete.txt"
            }
        }
    }

If you modify the file assets/my-robots-complete.txt it will update but if you empty it completely it won't.

My comment in #5 should not be a distraction. It's a valuable observation but should lead to a different issue being raised. It is a separate operation to the one flagged in this issue.

Test has been added