Add support to style function definitions with newlines before function stubs

CHANGES.md

@@ -26,6 +26,9 @@
 
 <!-- Changes to the parser or to version autodetection -->
 
+- Add support to style function definitions containing newlines before function stubs
+  (#4318)
+
 ### Performance
 
 <!-- Changes that improve Black's performance. -->

src/black/linegen.py

@@ -159,6 +159,8 @@ def visit_default(self, node: LN) -> Iterator[Line]:
                 normalize_numeric_literal(node)
             if node.type not in WHITESPACE:
                 self.current_line.append(node)
+            if node.type == token.DOT:
+                node.prefix = node.prefix.lstrip("\n")
         yield from super().visit_default(node)
 
     def visit_test(self, node: Node) -> Iterator[Line]:

tests/data/cases/stub_empty_line.py

@@ -0,0 +1,7 @@
+class C:
+    def f(self):
+
+        ...
+# output
+class C:
+    def f(self): ...

tests/data/cases/stub_many_empty_lines.py

@@ -0,0 +1,15 @@
+class C:
+    def f(self):
+
+
+
+
+
+
+
+
+
+        ...
+# output
+class C:
+    def f(self): ...