add option: allow_block_newline

src/black/__init__.py

@@ -268,6 +268,11 @@ def validate_regex(
     is_flag=True,
     help="Don't use trailing commas as a reason to split lines.",
 )
+@click.option(
+    "--allow-block-newline",
+    is_flag=True,
+    help="Allow a single opening newline after a block opens.",
+)
 @click.option(
     "--experimental-string-processing",
     is_flag=True,
@@ -439,6 +444,7 @@ def main(  # noqa: C901
     skip_source_first_line: bool,
     skip_string_normalization: bool,
     skip_magic_trailing_comma: bool,
+    allow_block_newline: bool,
     experimental_string_processing: bool,
     preview: bool,
     quiet: bool,
@@ -547,6 +553,7 @@ def main(  # noqa: C901
         skip_source_first_line=skip_source_first_line,
         string_normalization=not skip_string_normalization,
         magic_trailing_comma=not skip_magic_trailing_comma,
+        allow_block_newline=allow_block_newline,
         experimental_string_processing=experimental_string_processing,
         preview=preview,
         python_cell_magics=set(python_cell_magics),

src/black/lines.py

@@ -636,7 +636,11 @@ def _maybe_empty_lines(self, current_line: Line) -> Tuple[int, int]:
         ):
             return before, 1
 
-        if self.previous_line and self.previous_line.opens_block:
+        if (
+            not self.mode.allow_block_newline
+            and self.previous_line
+            and self.previous_line.opens_block
+        ):
             return 0, 0
         return before, 0
 

src/black/mode.py

@@ -181,6 +181,7 @@ class Mode:
     is_ipynb: bool = False
     skip_source_first_line: bool = False
     magic_trailing_comma: bool = True
+    allow_block_newline: bool = False
     experimental_string_processing: bool = False
     python_cell_magics: Set[str] = field(default_factory=set)
     preview: bool = False
@@ -220,6 +221,7 @@ def get_cache_key(self) -> str:
             str(int(self.is_ipynb)),
             str(int(self.skip_source_first_line)),
             str(int(self.magic_trailing_comma)),
+            str(int(self.allow_block_newline)),
             str(int(self.experimental_string_processing)),
             str(int(self.preview)),
             sha256((",".join(sorted(self.python_cell_magics))).encode()).hexdigest(),

src/blackd/__init__.py

@@ -33,6 +33,7 @@
 SKIP_SOURCE_FIRST_LINE = "X-Skip-Source-First-Line"
 SKIP_STRING_NORMALIZATION_HEADER = "X-Skip-String-Normalization"
 SKIP_MAGIC_TRAILING_COMMA = "X-Skip-Magic-Trailing-Comma"
+ALLOW_BLOCK_NEWLINE = "X-Allow_Block_Newline"
 PREVIEW = "X-Preview"
 FAST_OR_SAFE_HEADER = "X-Fast-Or-Safe"
 DIFF_HEADER = "X-Diff"
@@ -44,6 +45,7 @@
     SKIP_SOURCE_FIRST_LINE,
     SKIP_STRING_NORMALIZATION_HEADER,
     SKIP_MAGIC_TRAILING_COMMA,
+    ALLOW_BLOCK_NEWLINE,
     PREVIEW,
     FAST_OR_SAFE_HEADER,
     DIFF_HEADER,
@@ -113,6 +115,7 @@ async def handle(request: web.Request, executor: Executor) -> web.Response:
         skip_magic_trailing_comma = bool(
             request.headers.get(SKIP_MAGIC_TRAILING_COMMA, False)
         )
+        allow_block_newline = bool(request.headers.get(ALLOW_BLOCK_NEWLINE, False))
         skip_source_first_line = bool(
             request.headers.get(SKIP_SOURCE_FIRST_LINE, False)
         )
@@ -127,6 +130,7 @@ async def handle(request: web.Request, executor: Executor) -> web.Response:
             skip_source_first_line=skip_source_first_line,
             string_normalization=not skip_string_normalization,
             magic_trailing_comma=not skip_magic_trailing_comma,
+            allow_block_newline=allow_block_newline,
             preview=preview,
         )
         req_bytes = await request.content.read()

tests/data/miscellaneous/allow_newline_after_code_block_open.py

@@ -0,0 +1,214 @@
+import random
+
+
+def foo1():
+
+    print("Opening newline not removed with allow-block-newline")
+
+
+def foo2():
+
+
+
+    print("allow-block-newline keeps one line")
+
+
+def foo3():
+
+    print("Opening newline not removed with allow-block-newline")
+
+    print("There is a newline above me, and that's OK!")
+
+
+def foo4():
+
+    # There is a comment here
+
+    print("The newline above me should not be deleted!")
+
+
+class Foo:
+    def bar(self):
+
+        print("Opening newline not removed with allow-block-newline")
+
+
+for i in range(4):
+    print("no newline added here")
+
+for i in range(5):
+
+    print("Opening newline not removed with allow-block-newline")
+
+
+for i in range(6):
+
+
+
+    print("allow-block-newline keeps one line")
+
+
+for i in range(7):
+
+    for j in range(7):
+
+        print("Opening newline not removed with allow-block-newline")
+
+
+if random.randint(0, 3) == 0:
+
+    print("Opening newline not removed with allow-block-newline")
+
+
+if random.randint(0, 4) == 0:
+
+
+
+
+    print("allow-block-newline keeps one line")
+
+
+if random.randint(0, 5) == 0:
+    if random.uniform(0, 1) > 0.5:
+        print("no newlines added here")
+
+
+while True:
+
+    print("Opening newline not removed with allow-block-newline")
+
+
+while True:
+
+
+
+    print("allow-block-newline keeps one line")
+
+
+while True:
+
+    while False:
+
+        print("Opening newline not removed with allow-block-newline")
+
+
+with open("/path/to/file.txt", mode="w") as file:
+
+    file.write("Opening newline not removed with allow-block-newline")
+
+
+with open("/path/to/file.txt", mode="w") as file:
+
+
+
+    file.write("The newlines above me is about to be removed!")
+
+
+with open("/path/to/file.txt", mode="r") as read_file:
+
+    with open("/path/to/output_file.txt", mode="w") as write_file:
+
+        write_file.writelines(read_file.readlines())
+
+# output
+
+import random
+
+
+def foo1():
+
+    print("Opening newline not removed with allow-block-newline")
+
+
+def foo2():
+
+    print("allow-block-newline keeps one line")
+
+
+def foo3():
+
+    print("Opening newline not removed with allow-block-newline")
+
+    print("There is a newline above me, and that's OK!")
+
+
+def foo4():
+
+    # There is a comment here
+
+    print("The newline above me should not be deleted!")
+
+
+class Foo:
+    def bar(self):
+
+        print("Opening newline not removed with allow-block-newline")
+
+
+for i in range(4):
+    print("no newline added here")
+
+for i in range(5):
+
+    print("Opening newline not removed with allow-block-newline")
+
+
+for i in range(6):
+
+    print("allow-block-newline keeps one line")
+
+
+for i in range(7):
+
+    for j in range(7):
+
+        print("Opening newline not removed with allow-block-newline")
+
+
+if random.randint(0, 3) == 0:
+
+    print("Opening newline not removed with allow-block-newline")
+
+
+if random.randint(0, 4) == 0:
+
+    print("allow-block-newline keeps one line")
+
+
+if random.randint(0, 5) == 0:
+    if random.uniform(0, 1) > 0.5:
+        print("no newlines added here")
+
+
+while True:
+
+    print("Opening newline not removed with allow-block-newline")
+
+
+while True:
+
+    print("allow-block-newline keeps one line")
+
+
+while True:
+
+    while False:
+
+        print("Opening newline not removed with allow-block-newline")
+
+
+with open("/path/to/file.txt", mode="w") as file:
+
+    file.write("Opening newline not removed with allow-block-newline")
+
+
+with open("/path/to/file.txt", mode="w") as file:
+
+    file.write("The newlines above me is about to be removed!")
+
+
+with open("/path/to/file.txt", mode="r") as read_file:
+
+    with open("/path/to/output_file.txt", mode="w") as write_file:
+
+        write_file.writelines(read_file.readlines())

tests/test_format.py

@@ -203,3 +203,10 @@ def test_type_comment_syntax_error() -> None:
     source, expected = read_data("type_comments", "type_comment_syntax_error")
     assert_format(source, expected)
     black.assert_equivalent(source, expected)
+
+
+def test_optional_allow_block_newline() -> None:
+    """test allow_block_newline=True"""
+    source, expected = read_data("miscellaneous", "allow_newline_after_code_block_open")
+    mode = black.Mode(allow_block_newline=True)
+    assert_format(source, expected, mode)