Add a --dry-run option to backup_create that returns the size of items that will be backed up

data/actionsmap/yunohost.yml

@@ -890,6 +890,9 @@ backup:
                 --apps:
                     help: List of application names to backup (or all if none given)
                     nargs: "*"
+                --dry-run:
+                    help: "'Simulate' the backup and return the size details per item to backup"
+                    action: store_true
 
         ### backup_restore()
         restore:

locales/en.json

@@ -93,6 +93,7 @@
     "backup_copying_to_organize_the_archive": "Copying {size:s}MB to organize the archive",
     "backup_couldnt_bind": "Could not bind {src:s} to {dest:s}.",
     "backup_created": "Backup created",
+    "backup_create_size_estimation": "The archive will contain about {size} of data.",
     "backup_creation_failed": "Could not create the backup archive",
     "backup_csv_addition_failed": "Could not add files to backup into the CSV file",
     "backup_csv_creation_failed": "Could not create the CSV file needed for restoration",

src/yunohost/backup.py

@@ -2138,7 +2138,7 @@ class CustomBackupMethod(BackupMethod):
 @is_unit_operation()
 def backup_create(
     operation_logger,
-    name=None, description=None, methods=[], output_directory=None, system=[], apps=[]
+    name=None, description=None, methods=[], output_directory=None, system=[], apps=[], dry_run=False
 ):
     """
     Create a backup local archive
@@ -2220,8 +2220,15 @@ def backup_create(
     # Collect files to be backup (by calling app backup script / system hooks)
     backup_manager.collect_files()
 
+    if dry_run:
+        return {
+            "size": backup_manager.size,
+            "size_details": backup_manager.size_details
+        }
+
     # Apply backup methods on prepared files
     logger.info(m18n.n("backup_actually_backuping"))
+    logger.info(m18n.n("backup_create_size_estimation", size=binary_to_human(backup_manager.size) + "B"))
     backup_manager.backup()
 
     logger.success(m18n.n("backup_created"))