From d7a28dd78631fb962da95fb2d2de0e18ca6754a4 Mon Sep 17 00:00:00 2001
From: WMOkiishi <w.muneo.o@gmail.com>
Date: Sat, 18 Mar 2023 15:04:13 -0600
Subject: [PATCH] Enforce a blank line after a nested class in stubs (#3564)

---
 CHANGES.md                                     |  2 ++
 src/black/lines.py                             | 12 +++++++++---
 src/black/mode.py                              |  1 +
 tests/data/miscellaneous/nested_class_stub.pyi | 16 ++++++++++++++++
 tests/test_format.py                           |  6 ++++++
 5 files changed, 34 insertions(+), 3 deletions(-)
 create mode 100644 tests/data/miscellaneous/nested_class_stub.pyi

diff --git a/CHANGES.md b/CHANGES.md
index e2f21cf..029d0bc 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -23,6 +23,8 @@
   compared to their non-async version. (#3609)
 - `with` statements that contain two context managers will be consistently wrapped in
   parentheses (#3589)
+- For stubs, enforce one blank line after a nested class with a body other than just
+  `...` (#3564)
 
 ### Configuration
 
diff --git a/src/black/lines.py b/src/black/lines.py
index 66bba14..b2bdcc4 100644
--- a/src/black/lines.py
+++ b/src/black/lines.py
@@ -521,7 +521,7 @@ class EmptyLineTracker:
     mode: Mode
     previous_line: Optional[Line] = None
     previous_block: Optional[LinesBlock] = None
-    previous_defs: List[int] = field(default_factory=list)
+    previous_defs: List[Line] = field(default_factory=list)
     semantic_leading_comment: Optional[LinesBlock] = None
 
     def maybe_empty_lines(self, current_line: Line) -> LinesBlock:
@@ -577,12 +577,18 @@ class EmptyLineTracker:
         else:
             before = 0
         depth = current_line.depth
-        while self.previous_defs and self.previous_defs[-1] >= depth:
+        while self.previous_defs and self.previous_defs[-1].depth >= depth:
             if self.mode.is_pyi:
                 assert self.previous_line is not None
                 if depth and not current_line.is_def and self.previous_line.is_def:
                     # Empty lines between attributes and methods should be preserved.
                     before = min(1, before)
+                elif (
+                    Preview.blank_line_after_nested_stub_class in self.mode
+                    and self.previous_defs[-1].is_class
+                    and not self.previous_defs[-1].is_stub_class
+                ):
+                    before = 1
                 elif depth:
                     before = 0
                 else:
@@ -637,7 +643,7 @@ class EmptyLineTracker:
         self, current_line: Line, before: int
     ) -> Tuple[int, int]:
         if not current_line.is_decorator:
-            self.previous_defs.append(current_line.depth)
+            self.previous_defs.append(current_line)
         if self.previous_line is None:
             # Don't insert empty lines before the first line in the file.
             return 0, 0
diff --git a/src/black/mode.py b/src/black/mode.py
index 6af0417..0511676 100644
--- a/src/black/mode.py
+++ b/src/black/mode.py
@@ -154,6 +154,7 @@ class Preview(Enum):
     """Individual preview style features."""
 
     add_trailing_comma_consistently = auto()
+    blank_line_after_nested_stub_class = auto()
     hex_codes_in_unicode_sequences = auto()
     improved_async_statements_handling = auto()
     multiline_string_handling = auto()
diff --git a/tests/data/miscellaneous/nested_class_stub.pyi b/tests/data/miscellaneous/nested_class_stub.pyi
new file mode 100644
index 0000000..daf281b
--- /dev/null
+++ b/tests/data/miscellaneous/nested_class_stub.pyi
@@ -0,0 +1,16 @@
+class Outer:
+    class InnerStub: ...
+    outer_attr_after_inner_stub: int
+    class Inner:
+        inner_attr: int
+    outer_attr: int
+
+# output
+class Outer:
+    class InnerStub: ...
+    outer_attr_after_inner_stub: int
+
+    class Inner:
+        inner_attr: int
+
+    outer_attr: int
diff --git a/tests/test_format.py b/tests/test_format.py
index ab849aa..3a6cbc9 100644
--- a/tests/test_format.py
+++ b/tests/test_format.py
@@ -186,6 +186,12 @@ def test_stub() -> None:
     assert_format(source, expected, mode)
 
 
+def test_nested_class_stub() -> None:
+    mode = replace(DEFAULT_MODE, is_pyi=True, preview=True)
+    source, expected = read_data("miscellaneous", "nested_class_stub.pyi")
+    assert_format(source, expected, mode)
+
+
 def test_power_op_newline() -> None:
     # requires line_length=0
     source, expected = read_data("miscellaneous", "power_op_newline")
-- 
2.39.2