Fix a bug where two empty lines were added before class's leading com…

…ment but after decorators.

src/black/lines.py

@@ -506,10 +506,9 @@ def maybe_empty_lines(self, current_line: Line) -> LinesBlock:
 
         # Maintain the semantic_leading_comment state.
         if current_line.is_comment:
-            if (
-                self.semantic_leading_comment is None
-                or self.previous_line is None
-                or (before and not self.previous_line.is_decorator)
+            if self.previous_line is None or (
+                not self.previous_line.is_decorator
+                and (self.semantic_leading_comment is None or before)
             ):
                 self.semantic_leading_comment = block
         elif not current_line.is_decorator:

tests/data/preview/comments9.py

@@ -40,6 +40,7 @@ class MyClassAfterAnotherClassWithDocstring:
 @deco2(with_args=True)
 # leading 3
 @deco3
+# leading 4
 def decorated():
     pass
 
@@ -52,6 +53,20 @@ def decorated():
 
 # leading 3 that already has an empty line
 @deco3
+# leading 4
+def decorated_with_split_leading_comments():
+    pass
+
+
+some = statement
+# leading 1
+@deco1
+# leading 2
+@deco2(with_args=True)
+# leading 3
+@deco3
+
+# leading 4 that already has an empty line
 def decorated_with_split_leading_comments():
     pass
 
@@ -139,6 +154,7 @@ class MyClassAfterAnotherClassWithDocstring:
 @deco2(with_args=True)
 # leading 3
 @deco3
+# leading 4
 def decorated():
     pass
 
@@ -153,6 +169,22 @@ def decorated():
 
 # leading 3 that already has an empty line
 @deco3
+# leading 4
+def decorated_with_split_leading_comments():
+    pass
+
+
+some = statement
+
+
+# leading 1
+@deco1
+# leading 2
+@deco2(with_args=True)
+# leading 3
+@deco3
+
+# leading 4 that already has an empty line
 def decorated_with_split_leading_comments():
     pass