fix issue psf#251: isort removes newlines before standalone comments …

…if the following line is an import of the same group

.gitignore

@@ -4,6 +4,7 @@ _build
 .vscode
 docs/_static/pypi.svg
 .tox
+.idea
 __pycache__
 black.egg-info
 build/

black.py

@@ -53,6 +53,7 @@
 
 __version__ = "19.3b0"
 DEFAULT_LINE_LENGTH = 88
+DEFAULT_IMPORT_MODE = 0
 DEFAULT_EXCLUDES = (
     r"/(\.eggs|\.git|\.hg|\.mypy_cache|\.nox|\.tox|\.venv|_build|buck-out|build|dist)/"
 )
@@ -182,6 +183,7 @@ class Feature(Enum):
 @dataclass
 class FileMode:
     target_versions: Set[TargetVersion] = Factory(set)
+    import_mode: int = DEFAULT_IMPORT_MODE
     line_length: int = DEFAULT_LINE_LENGTH
     string_normalization: bool = True
     is_pyi: bool = False
@@ -359,6 +361,14 @@ def read_pyproject_toml(
     ),
     is_eager=True,
 )
+@click.option(
+    "--import-mode",
+    default=DEFAULT_IMPORT_MODE,
+    help=(
+        "0-handle imports as usual. Default value\n"
+        "1-skip adding empty line between standalone comment and import\n"
+    ),
+)
 @click.option(
     "--config",
     type=click.Path(
@@ -370,6 +380,7 @@ def read_pyproject_toml(
 )
 @click.pass_context
 def main(
+    import_mode: int,
     ctx: click.Context,
     code: Optional[str],
     line_length: int,
@@ -406,6 +417,7 @@ def main(
         versions = set()
     mode = FileMode(
         target_versions=versions,
+        import_mode=import_mode,
         line_length=line_length,
         is_pyi=pyi,
         string_normalization=not skip_string_normalization,
@@ -721,7 +733,7 @@ def format_str(src_contents: str, *, mode: FileMode) -> FileContent:
         is_pyi=mode.is_pyi,
         normalize_strings=mode.string_normalization,
     )
-    elt = EmptyLineTracker(is_pyi=mode.is_pyi)
+    elt = EmptyLineTracker(is_pyi=mode.is_pyi, import_mode=mode.import_mode)
     empty_line = Line()
     after = 0
     split_line_features = {
@@ -1464,6 +1476,7 @@ class EmptyLineTracker:
     are consumed by `maybe_empty_lines()` and included in the computation.
     """
 
+    import_mode: int = DEFAULT_IMPORT_MODE
     is_pyi: bool = False
     previous_line: Optional[Line] = None
     previous_after: int = 0
@@ -1504,7 +1517,8 @@ def _maybe_empty_lines(self, current_line: Line) -> Tuple[int, int]:
             return self._maybe_empty_lines_for_class_or_def(current_line, before)
 
         if (
-            self.previous_line
+            self.import_mode == 0
+            and self.previous_line
             and self.previous_line.is_import
             and not current_line.is_import
             and depth == self.previous_line.depth

tests/data/import_handling_issue_251.py

@@ -0,0 +1,112 @@
+"""The asyncio package, tracking PEP 3156."""
+
+# flake8: noqa
+
+from logging import (
+    ERROR,
+)
+import sys
+
+# This relies on each of the submodules having an __all__ variable.
+from .base_events import *
+from .coroutines import *
+from .events import *  # comment here
+# bugfix_1
+from .futures import *
+from .locks import *  # comment here
+from .protocols import *
+# bugfix_2
+from ..runners import *  # comment here
+from ..queues import *
+from ..streams import *
+
+from some_library import (
+    Just, Enough, Libraries, To, Fit, In, This, Nice, Split, Which, We, No, Longer, Use
+)
+from name_of_a_company.extremely_long_project_name.component.ttypes import CuteLittleServiceHandlerFactoryyy
+from name_of_a_company.extremely_long_project_name.extremely_long_component_name.ttypes import *
+
+from .a.b.c.subprocess import *
+from . import (tasks)
+from . import (A, B, C)
+from . import SomeVeryLongNameAndAllOfItsAdditionalLetters1, \
+              SomeVeryLongNameAndAllOfItsAdditionalLetters2
+# bugfix_3
+__all__ = (
+    base_events.__all__
+    + coroutines.__all__
+    + events.__all__
+    + futures.__all__
+    + locks.__all__
+    + protocols.__all__
+    + runners.__all__
+    + queues.__all__
+    + streams.__all__
+    + tasks.__all__
+)
+
+
+# output
+
+
+"""The asyncio package, tracking PEP 3156."""
+
+# flake8: noqa
+
+from logging import ERROR
+import sys
+
+# This relies on each of the submodules having an __all__ variable.
+from .base_events import *
+from .coroutines import *
+from .events import *  # comment here
+# bugfix_1
+from .futures import *
+from .locks import *  # comment here
+from .protocols import *
+# bugfix_2
+from ..runners import *  # comment here
+from ..queues import *
+from ..streams import *
+
+from some_library import (
+    Just,
+    Enough,
+    Libraries,
+    To,
+    Fit,
+    In,
+    This,
+    Nice,
+    Split,
+    Which,
+    We,
+    No,
+    Longer,
+    Use,
+)
+from name_of_a_company.extremely_long_project_name.component.ttypes import (
+    CuteLittleServiceHandlerFactoryyy,
+)
+from name_of_a_company.extremely_long_project_name.extremely_long_component_name.ttypes import *
+
+from .a.b.c.subprocess import *
+from . import tasks
+from . import A, B, C
+from . import (
+    SomeVeryLongNameAndAllOfItsAdditionalLetters1,
+    SomeVeryLongNameAndAllOfItsAdditionalLetters2,
+)
+# bugfix_3
+__all__ = (
+    base_events.__all__
+    + coroutines.__all__
+    + events.__all__
+    + futures.__all__
+    + locks.__all__
+    + protocols.__all__
+    + runners.__all__
+    + queues.__all__
+    + streams.__all__
+    + tasks.__all__
+)

tests/test_black.py

@@ -596,6 +596,14 @@ def test_tuple_assign(self) -> None:
         black.assert_equivalent(source, actual)
         black.assert_stable(source, actual, black.FileMode())
 
+    @patch("black.dump_to_file", dump_to_stderr)
+    def test__maybe_empty_lines(self) -> None:
+        source, expected = read_data("import_handling_issue_251")
+        actual = fs(source, mode=black.FileMode(import_mode=1))
+        self.assertFormatEqual(expected, actual)
+        black.assert_equivalent(source, actual)
+        black.assert_stable(source, actual, black.FileMode(import_mode=1))
+
     def test_tab_comment_indentation(self) -> None:
         contents_tab = "if 1:\n\tif 2:\n\t\tpass\n\t# comment\n\tpass\n"
         contents_spc = "if 1:\n    if 2:\n        pass\n    # comment\n    pass\n"