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

yilei · web-flow · commit 01b8d3d4095e · 2023-06-15T17:08:26.000-07:00
Fix psf#3638: Do not add trailing commas to return type annotations using PEP 604 unions.
diff --git 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
@@ -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
@@ -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

Original file line number	Diff line number	Diff line change
`@@ -918,6 +918,13 @@ def bracket_split_build_line(`
`918`	`918`	`)`
`919`	`919`	`if isinstance(node, Node) and isinstance(node.prev_sibling, Leaf)`
`920`	`920`	`)`
	`921`	`+ # Except the false negatives above for PEP 604 unions where we`
	`922`	`+ # can't add the comma.`
	`923`	`+ and not (`
	`924`	`+ leaves[0].parent`
	`925`	`+ and leaves[0].parent.next_sibling`
	`926`	`+ and leaves[0].parent.next_sibling.type == token.VBAR`
	`927`	`+ )`
`921`	`928`	`)`
`922`	`929`
`923`	`930`	`if original.is_import or no_commas:`