"--pretend" (dry run) flag for update

beets/ui/commands.py

@@ -692,7 +692,7 @@ default_commands.append(list_cmd)
 
 # update: Update library contents according to on-disk tags.
 
-def update_items(lib, query, album, move, color):
+def update_items(lib, query, album, move, color, pretend):
     """For all the items matched by the query, update the library to
     reflect the item's embedded tags.
     """
@@ -704,7 +704,8 @@ def update_items(lib, query, album, move, color):
         # Item deleted?
         if not os.path.exists(syspath(item.path)):
             print_(u'X %s - %s' % (item.artist, item.title))
-            lib.remove(item, True)
+            if not pretend:
+                lib.remove(item, True)
             affected_albums.add(item.album_id)
             continue
 
@@ -731,6 +732,10 @@ def update_items(lib, query, album, move, color):
             for key, (oldval, newval) in changes.iteritems():
                 _showdiff(key, oldval, newval, color)
 
+            # If we're just pretending, then don't move or save.
+            if pretend:
+                continue
+
             # Move the item if it's in the library.
             if move and lib.directory in ancestry(item.path):
                 lib.move(item)
@@ -738,6 +743,10 @@ def update_items(lib, query, album, move, color):
             lib.store(item)
             affected_albums.add(item.album_id)
 
+    # Skip album changes while pretending.
+    if pretend:
+        return
+
     # Modify affected albums to reflect changes in their items.
     for album_id in affected_albums:
         if album_id is None: # Singletons.
@@ -765,9 +774,11 @@ update_cmd.parser.add_option('-a', '--album', action='store_true',
     help='show matching albums instead of tracks')
 update_cmd.parser.add_option('-M', '--nomove', action='store_false',
     default=True, dest='move', help="don't move files in library")
+update_cmd.parser.add_option('-p', '--pretend', action='store_true',
+    help="show all changes but do nothing")
 def update_func(lib, config, opts, args):
     color = ui.config_val(config, 'beets', 'color', DEFAULT_COLOR, bool)
-    update_items(lib, decargs(args), opts.album, opts.move, color)
+    update_items(lib, decargs(args), opts.album, opts.move, color, opts.pretend)
 update_cmd.func = update_func
 default_commands.append(update_cmd)
 

docs/reference/cli.rst

@@ -180,6 +180,10 @@ This will scan all the matched files and read their tags, populating the
 database with the new values. By default, files will be renamed according to
 their new metadata; disable this with ``-M``.
 
+To perform a "dry run" an update, just use the ``-p`` (for "pretend") flag. This
+will show you all the proposed changes but won't actually change anything on
+disk.
+
 stats
 -----
 ::

test/test_ui.py

@@ -296,7 +296,7 @@ class UpdateTest(unittest.TestCase, _common.ExtraAsserts):
 
     def _update(self, query=(), album=False, move=False):
         self.io.addinput('y')
-        commands.update_items(self.lib, query, album, move, True)
+        commands.update_items(self.lib, query, album, move, True, False)
 
     def test_delete_removes_item(self):
         self.assertTrue(list(self.lib.items()))