If you try to upload a new file with the same name as an existing asset file in the same location, the CMS should warn you about the name collision. We currently do something similar to this for content files: https://github.com/plentico/plenti/issues/202. For asset files however, you set the name for the file locally on your computer, not through the CMS (although you do set the path in the CMS and it might be nice to be able to rename files in the future). For now we could just display a warning that "file failed to upload because a file with the same name already exists". It would be on the user to either delete the existing file, or change the name of the upload file on their computer.
If you try to upload a new file with the same name as an existing asset file in the same location, the CMS should warn you about the name collision. We currently do something similar to this for content files: https://github.com/plentico/plenti/issues/202. For asset files however, you set the name for the file locally on your computer, not through the CMS (although you do set the path in the CMS and it might be nice to be able to rename files in the future). For now we could just display a warning that "file failed to upload because a file with the same name already exists". It would be on the user to either delete the existing file, or change the name of the upload file on their computer.