Do not add trailing commas to return type annotations using PEP 604 unions (#3735)

Fix #3638: Do not add trailing commas to return type annotations using PEP 604 unions.

diff --git a/CHANGES.md b/CHANGES.md
index 658faad3a78bba23fe62346f66336dd9f88b3c8f..fd4d911287dcb40abe285442bb9d2c72ad48ceca 100644 (file)
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -10,6 +10,9 @@
 
 <!-- Changes that affect Black's stable style -->
 
+- Fix a bug where an illegal trailing comma was added to return type annotations using
+  PEP 604 unions (#3735)
+
 ### Preview style
 
 <!-- Changes that affect Black's preview style -->

diff --git a/src/black/linegen.py b/src/black/linegen.py
index 0091cbb3bd1d3195d3bc06fed11aeac280b987bf..ad21307c311b83b0e0eb964b34ae6149cfcb0cee 100644 (file)
--- a/src/black/linegen.py
+++ b/src/black/linegen.py
@@ -918,6 +918,13 @@ def bracket_split_build_line(
                     )
                     if isinstance(node, Node) and isinstance(node.prev_sibling, Leaf)
                 )
+                # Except the false negatives above for PEP 604 unions where we
+                # can't add the comma.
+                and not (
+                    leaves[0].parent
+                    and leaves[0].parent.next_sibling
+                    and leaves[0].parent.next_sibling.type == token.VBAR
+                )
             )
 
             if original.is_import or no_commas:

diff --git a/tests/data/simple_cases/pep_604.py b/tests/data/simple_cases/pep_604.py
new file mode 100644 (file)
index 0000000..b68d59d
--- /dev/null
+++ b/tests/data/simple_cases/pep_604.py
@@ -0,0 +1,25 @@
+def some_very_long_name_function() -> my_module.Asdf | my_module.AnotherType | my_module.YetAnotherType | None:
+    pass
+
+
+def some_very_long_name_function() -> my_module.Asdf | my_module.AnotherType | my_module.YetAnotherType | my_module.EvenMoreType | None:
+    pass
+
+
+# output
+
+
+def some_very_long_name_function() -> (
+    my_module.Asdf | my_module.AnotherType | my_module.YetAnotherType | None
+):
+    pass
+
+
+def some_very_long_name_function() -> (
+    my_module.Asdf
+    | my_module.AnotherType
+    | my_module.YetAnotherType
+    | my_module.EvenMoreType
+    | None
+):
+    pass