Preview: Keep requiring two empty lines between module-level docstring and first function or class definition (#4028)

Fixes #4027.

Author: yilei

CHANGES.md

@@ -19,6 +19,8 @@
   indented less (#3964)
 - Multiline list and dict unpacking as the sole argument to a function is now also
   indented less (#3992)
+- Keep requiring two empty lines between module-level docstring and first function or
+  class definition. (#4028)
 
 ### Configuration
 

src/black/lines.py

@@ -578,6 +578,7 @@ def maybe_empty_lines(self, current_line: Line) -> LinesBlock:
             and self.previous_block.previous_block is None
             and len(self.previous_block.original_line.leaves) == 1
             and self.previous_block.original_line.is_triple_quoted_string
+            and not (current_line.is_class or current_line.is_def)
         ):
             before = 1
 

tests/data/cases/module_docstring_followed_by_class.py

@@ -0,0 +1,11 @@
+# flags: --preview
+"""Two blank lines between module docstring and a class."""
+class MyClass:
+    pass
+
+# output
+"""Two blank lines between module docstring and a class."""
+
+
+class MyClass:
+    pass

tests/data/cases/module_docstring_followed_by_function.py

@@ -0,0 +1,11 @@
+# flags: --preview
+"""Two blank lines between module docstring and a function def."""
+def function():
+    pass
+
+# output
+"""Two blank lines between module docstring and a function def."""
+
+
+def function():
+    pass