change how blank lines work

src/black/lines.py

@@ -530,11 +530,11 @@ def _maybe_empty_lines_for_class_or_def(
             return 0, 0
 
         if self.is_pyi:
-            if self.previous_line.depth > current_line.depth:
-                newlines = 0 if current_line.depth else 1
-            elif current_line.is_class or self.previous_line.is_class:
-                if current_line.depth:
+            if current_line.is_class or self.previous_line.is_class:
+                if self.previous_line.depth < current_line.depth:
                     newlines = 0
+                elif self.previous_line.depth > current_line.depth:
+                    newlines = 1
                 elif current_line.is_stub_class and self.previous_line.is_stub_class:
                     # No blank line between classes with an empty body
                     newlines = 0
@@ -551,6 +551,8 @@ def _maybe_empty_lines_for_class_or_def(
                     # Blank line between a block of functions (maybe with preceding
                     # decorators) and a block of non-functions
                     newlines = 1
+            elif self.previous_line.depth > current_line.depth:
+                newlines = 1
             else:
                 newlines = 0
         else:

tests/data/stub.pyi

@@ -96,24 +96,31 @@ def h(): ...
 if sys.version_info >= (3, 8):
     class E:
         def f(self): ...
+
     class F:
         def f(self): ...
+
     class G: ...
     class H: ...
 
 else:
     class I: ...
     class J: ...
+
     def f(): ...
+
     class K:
         def f(self): ...
+
     def f(): ...
 
 class Nested:
     class dirty: ...
     class little: ...
+
     class secret:
         def who_has_to_know(self): ...
+
     def verse(self): ...
 
 class CondMethod:
@@ -122,8 +129,10 @@ class CondMethod:
         def g(self): ...
     else:
         def g(self): ...
+
     def h(self): ...
     def i(self): ...
     if sys.version_info >= (3, 8):
         def j(self): ...
+
     def k(self): ...