on-save-file in editor:backup-autosave-mixin

Called just before the editor is saved to a file, after calling can-save-file? to verify that the save is allowed. See also after-save-file.

• (send an-editor:backup-autosave-mixin on-save-file filename format) -> bool
     filename : string
     format : symbol in '(guess standard text text-force-cr same copy)

  The filename argument is the name the file will be saved to. See load-file for information about format.

  If a backup file has not been created this session for this file, deletes any existing backup file and copies the old save file into the backup file. For the backup file's name, see path-utils:generate-backup-name