Remove blank lines before class docstring (#3692)

CHANGES.md

@@ -16,6 +16,7 @@
 
 - Implicitly concatenated strings used as function args are no longer wrapped inside
   parentheses (#3640)
+- Remove blank lines between a class definition and its docstring (#3692)
 
 ### Configuration
 

src/black/lines.py

@@ -634,6 +634,8 @@ def _maybe_empty_lines(self, current_line: Line) -> Tuple[int, int]:
             and self.previous_line.is_class
             and current_line.is_triple_quoted_string
         ):
+            if Preview.no_blank_line_before_class_docstring in current_line.mode:
+                return 0, 1
             return before, 1
 
         if self.previous_line and self.previous_line.opens_block:

src/black/mode.py

@@ -158,6 +158,7 @@ class Preview(Enum):
     hex_codes_in_unicode_sequences = auto()
     improved_async_statements_handling = auto()
     multiline_string_handling = auto()
+    no_blank_line_before_class_docstring = auto()
     prefer_splitting_right_hand_side_of_assignments = auto()
     # NOTE: string_processing requires wrap_long_dict_values_in_parens
     # for https://github.com/psf/black/issues/3117 to be fixed.

tests/data/preview/no_blank_line_before_docstring.py

@@ -0,0 +1,58 @@
+def line_before_docstring():
+
+    """Please move me up"""
+
+
+class LineBeforeDocstring:
+
+    """Please move me up"""
+
+
+class EvenIfThereIsAMethodAfter:
+
+    """I'm the docstring"""
+    def method(self):
+        pass
+
+
+class TwoLinesBeforeDocstring:
+
+
+    """I want to be treated the same as if I were closer"""
+
+
+class MultilineDocstringsAsWell:
+
+    """I'm so far
+
+    and on so many lines...
+    """
+
+
+# output
+
+
+def line_before_docstring():
+    """Please move me up"""
+
+
+class LineBeforeDocstring:
+    """Please move me up"""
+
+
+class EvenIfThereIsAMethodAfter:
+    """I'm the docstring"""
+
+    def method(self):
+        pass
+
+
+class TwoLinesBeforeDocstring:
+    """I want to be treated the same as if I were closer"""
+
+
+class MultilineDocstringsAsWell:
+    """I'm so far
+
+    and on so many lines...
+    """