Adds a zero_disc_if_single_disc to the zero plugin

beetsplug/zero.py

@@ -41,6 +41,7 @@ def __init__(self):
                 "fields": [],
                 "keep_fields": [],
                 "update_database": False,
+                "omit_single_disc": False,
             }
         )
 
@@ -123,9 +124,14 @@ def set_fields(self, item, tags):
         """
         fields_set = False
 
+        if "disc" in tags and self.config["omit_single_disc"].get(bool):
+            if item.disctotal == 1:
+                fields_set = True
+                self._log.debug("disc: {.disc} -> None", item)
+                tags["disc"] = None
+
         if not self.fields_to_progs:
-            self._log.warning("no fields, nothing to do")
-            return False
+            self._log.warning("no fields list to remove")
 
         for field, progs in self.fields_to_progs.items():
             if field in tags:

docs/changelog.rst

@@ -9,6 +9,10 @@ Unreleased
 
 New features:
 
+- :doc:`plugins/zero`: Add new configuration option, ``omit_single_disc``, to
+  allow zeroing the disc number on write for single-disc albums. Defaults to
+  False.
+
 Bug fixes:
 
 For packagers:

docs/plugins/zero.rst

@@ -31,6 +31,9 @@ to nullify and the conditions for nullifying them:
   ``keep_fields``---not both!
 - To conditionally filter a field, use ``field: [regexp, regexp]`` to specify
   regular expressions.
+- Set ``omit_single_disc`` to ``True`` to omit writing the ``disc`` number for
+  albums with only a single disc (``disctotal == 1``). By default, beets will
+  number the disc even if the album contains only one disc in total.
 - By default this plugin only affects files' tags; the beets database is left
   unchanged. To update the tags in the database, set the ``update_database``
   option to true.

test/plugins/test_zero.py

@@ -249,6 +249,54 @@ def test_fields_removes_preserved_tags(self):
 
         assert "id" not in z.fields_to_progs
 
+    def test_omit_single_disc_with_tags_single(self):
+        item = self.add_item_fixture(
+            disctotal=1, disc=1, comments="test comment"
+        )
+        item.write()
+        with self.configure_plugin(
+            {"omit_single_disc": True, "fields": ["comments"]}
+        ):
+            item.write()
+
+        mf = MediaFile(syspath(item.path))
+        assert mf.comments is None
+        assert mf.disc == 0
+
+    def test_omit_single_disc_with_tags_multi(self):
+        item = self.add_item_fixture(
+            disctotal=4, disc=1, comments="test comment"
+        )
+        item.write()
+        with self.configure_plugin(
+            {"omit_single_disc": True, "fields": ["comments"]}
+        ):
+            item.write()
+
+        mf = MediaFile(syspath(item.path))
+        assert mf.comments is None
+        assert mf.disc == 1
+
+    def test_omit_single_disc_only_change_single(self):
+        item = self.add_item_fixture(disctotal=1, disc=1)
+        item.write()
+
+        with self.configure_plugin({"omit_single_disc": True}):
+            item.write()
+
+        mf = MediaFile(syspath(item.path))
+        assert mf.disc == 0
+
+    def test_omit_single_disc_only_change_multi(self):
+        item = self.add_item_fixture(disctotal=4, disc=1)
+        item.write()
+
+        with self.configure_plugin({"omit_single_disc": True}):
+            item.write()
+
+        mf = MediaFile(syspath(item.path))
+        assert mf.disc == 1
+
     def test_empty_query_n_response_no_changes(self):
         item = self.add_item_fixture(
             year=2016, day=13, month=3, comments="test comment"