Two blank lines after an import should be reduced to one

CHANGES.md

@@ -17,6 +17,8 @@
 
 <!-- Changes that affect Black's preview style -->
 
+- Collapse multiple lines into 1 after import (#4489)
+
 ### Configuration
 
 <!-- Changes to how Black can be configured -->

docs/the_black_code_style/future_style.md

@@ -38,6 +38,8 @@ Currently, the following features are included in the preview style:
   blocks when the line is too long
 - `pep646_typed_star_arg_type_var_tuple`: fix type annotation spacing between * and more
   complex type variable tuple (i.e. `def fn(*args: *tuple[*Ts, T]) -> None: pass`)
+- `always_one_newline_after_import`: Always force one newline after import statements
+  except for when the line after the import is a comment or an import statement
 
 (labels/unstable-features)=
 

src/black/lines.py

@@ -605,7 +605,17 @@ 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
+                and Preview.always_one_newline_after_import in self.mode
+                else min(before, max_allowed)
+            )
             first_leaf.prefix = ""
         else:
             before = 0

src/black/mode.py

@@ -211,6 +211,7 @@ class Preview(Enum):
     remove_redundant_guard_parens = auto()
     parens_for_long_if_clauses_in_case_block = auto()
     pep646_typed_star_arg_type_var_tuple = auto()
+    always_one_newline_after_import = auto()
 
 
 UNSTABLE_FEATURES: set[Preview] = {

src/black/resources/black.schema.json

@@ -91,7 +91,8 @@
           "docstring_check_for_newline",
           "remove_redundant_guard_parens",
           "parens_for_long_if_clauses_in_case_block",
-          "pep646_typed_star_arg_type_var_tuple"
+          "pep646_typed_star_arg_type_var_tuple",
+          "always_one_newline_after_import"
         ]
       },
       "description": "Enable specific features included in the `--unstable` style. Requires `--preview`. No compatibility guarantees are provided on the behavior or existence of any unstable features."

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

tests/data/cases/preview_import_line_collapse.py

@@ -0,0 +1,13 @@
+# flags: --preview
+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_import_line_collapse_3_to_1.py

@@ -0,0 +1,14 @@
+# flags: --preview
+from middleman.authentication import validate_oauth_token
+
+
+
+logger = logging.getLogger(__name__)
+
+
+# output
+
+
+from middleman.authentication import validate_oauth_token
+
+logger = logging.getLogger(__name__)