Collapse multiple lines after import into single line

CHANGES.md

@@ -10,6 +10,8 @@
 
 <!-- Changes that affect Black's stable style -->
 
+- Collapse multiple lines into 1 after import (#4488)
+
 ### Preview style
 
 <!-- Changes that affect Black's preview style -->

src/black/lines.py

@@ -605,7 +605,16 @@ def _maybe_empty_lines(self, current_line: Line) -> tuple[int, int]:  # noqa: C9
             # Consume the first leaf's extra newlines.
             first_leaf = current_line.leaves[0]
             before = first_leaf.prefix.count("\n")
-            before = min(before, max_allowed)
+            before = (
+                1
+                if self.previous_line
+                and self.previous_line.is_import
+                and self.previous_line.depth == 0
+                and current_line.depth == 0
+                and not current_line.is_import
+                and not current_line.is_comment
+                else min(before, max_allowed)
+            )
             first_leaf.prefix = ""
         else:
             before = 0

tests/data/cases/import_line_collapse.py

@@ -0,0 +1,12 @@
+from middleman.authentication import validate_oauth_token
+
+
+logger = logging.getLogger(__name__)
+
+
+# output
+
+
+from middleman.authentication import validate_oauth_token
+
+logger = logging.getLogger(__name__)

tests/data/cases/import_line_collapse_3_to_1.py

@@ -0,0 +1,13 @@
+from middleman.authentication import validate_oauth_token
+
+
+
+logger = logging.getLogger(__name__)
+
+
+# output
+
+
+from middleman.authentication import validate_oauth_token
+
+logger = logging.getLogger(__name__)

tests/data/cases/preview_comments7.py

@@ -177,7 +177,6 @@ def test_fails_invalid_post_data(
     MyLovelyCompanyTeamProjectComponent as component,  # DRY
 )
 
-
 result = 1  # look ma, no comment migration xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
 
 result = 1  # look ma, no comment migration xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx