Allow empty lines at beginning of blocks (again) (#4060)

CHANGES.md

@@ -17,6 +17,8 @@
 - Standalone form feed characters at the module level are no longer removed (#4021)
 - Additional cases of immediately nested tuples, lists, and dictionaries are now
   indented less (#4012)
+- Allow empty lines at the beginning of all blocks, except immediately before a
+  docstring (#4060)
 - Fix crash in preview mode when using a short `--line-length` (#4086)
 
 ### Configuration

src/black/lines.py

@@ -689,18 +689,14 @@ def _maybe_empty_lines(self, current_line: Line) -> Tuple[int, int]:
                 return 0, 1
             return before, 1
 
+        # In preview mode, always allow blank lines, except right before a function
+        # docstring
         is_empty_first_line_ok = (
-            Preview.allow_empty_first_line_before_new_block_or_comment
+            Preview.allow_empty_first_line_in_block in current_line.mode
-            in current_line.mode
             and (
-                # If it's a standalone comment
+                not is_docstring(current_line.leaves[0])
-                current_line.leaves[0].type == STANDALONE_COMMENT
-                # If it opens a new block
-                or current_line.opens_block
-                # If it's a triple quote comment (but not at the start of a funcdef)
                 or (
-                    is_docstring(current_line.leaves[0])
+                    self.previous_line
-                    and self.previous_line
                     and self.previous_line.leaves[0]
                     and self.previous_line.leaves[0].parent
                     and not is_funcdef(self.previous_line.leaves[0].parent)

src/black/mode.py

@@ -191,7 +191,7 @@ class Preview(Enum):
     accept_raw_docstrings = auto()
     fix_power_op_line_length = auto()
     hug_parens_with_braces_and_square_brackets = auto()
-    allow_empty_first_line_before_new_block_or_comment = auto()
+    allow_empty_first_line_in_block = auto()
     single_line_format_skip_with_multiple_comments = auto()
     long_case_block_line_splitting = auto()
     allow_form_feeds = auto()

tests/data/cases/preview_allow_empty_first_line.py

@@ -51,6 +51,17 @@ def baz():
     if x:
         a = 123
 
+def quux():
+
+    new_line = here
+
+
+class Cls:
+
+    def method(self):
+
+        pass
+
 # output
 
 def foo():
@@ -104,3 +115,14 @@ def baz():
     # OK
     if x:
         a = 123
+
+
+def quux():
+
+    new_line = here
+
+
+class Cls:
+    def method(self):
+
+        pass

tests/data/cases/preview_form_feeds.py

@@ -198,6 +198,7 @@ def foo():
 
 # form feeds are prohibited inside blocks, or on a line with nonwhitespace
 def bar(a=1, b: bool = False):
+
     pass