Remove newline after code block open (#3035)

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>

AUTHORS.md

@@ -148,6 +148,7 @@ Multiple contributions by:
 - [Rishikesh Jha](mailto:rishijha424@gmail.com)
 - [Rupert Bedford](mailto:rupert@rupertb.com)
 - Russell Davis
+- [Sagi Shadur](mailto:saroad2@gmail.com)
 - [Rémi Verschelde](mailto:rverschelde@gmail.com)
 - [Sami Salonen](mailto:sakki@iki.fi)
 - [Samuel Cormier-Iijima](mailto:samuel@cormier-iijima.com)

CHANGES.md

@@ -21,6 +21,7 @@
 - Remove redundant parentheses around awaited objects (#2991)
 - Parentheses around return annotations are now managed (#2990)
 - Remove unnecessary parentheses from `with` statements (#2926)
+- Remove trailing newlines after code block open (#3035)
 
 ### _Blackd_
 

docs/the_black_code_style/future_style.md

@@ -49,3 +49,28 @@ plain strings. User-made splits are respected when they do not exceed the line l
 limit. Line continuation backslashes are converted into parenthesized strings.
 Unnecessary parentheses are stripped. The stability and status of this feature is
 tracked in [this issue](https://github.com/psf/black/issues/2188).
+
+### Removing trailing newlines after code block open
+
+_Black_ will remove trailing newlines after code block openings. That means that the
+following code:
+
+```python
+def my_func():
+
+    print("The line above me will be deleted!")
+
+    print("But the line above me won't!")
+```
+
+Will be changed to:
+
+```python
+def my_func():
+    print("The line above me will be deleted!")
+
+    print("But the line above me won't!")
+```
+
+This new feature will be applied to **all code blocks**: `def`, `class`, `if`, `for`,
+`while`, `with`, `case` and `match`.

src/black/lines.py

@@ -168,6 +168,13 @@ def is_triple_quoted_string(self) -> bool:
             and self.leaves[0].value.startswith(('"""', "'''"))
         )
 
+    @property
+    def opens_block(self) -> bool:
+        """Does this line open a new level of indentation."""
+        if len(self.leaves) == 0:
+            return False
+        return self.leaves[-1].type == token.COLON
+
     def contains_standalone_comments(self, depth_limit: int = sys.maxsize) -> bool:
         """If so, needs to be split before emitting."""
         for leaf in self.leaves:
@@ -513,6 +520,12 @@ def _maybe_empty_lines(self, current_line: Line) -> Tuple[int, int]:
         ):
             return before, 1
 
+        if (
+            Preview.remove_block_trailing_newline in current_line.mode
+            and self.previous_line
+            and self.previous_line.opens_block
+        ):
+            return 0, 0
         return before, 0
 
     def _maybe_empty_lines_for_class_or_def(

src/black/mode.py

@@ -150,6 +150,7 @@ class Preview(Enum):
     one_element_subscript = auto()
     annotation_parens = auto()
     long_docstring_quotes_on_newline = auto()
+    remove_block_trailing_newline = auto()
 
 
 class Deprecated(UserWarning):

tests/data/preview/remove_newline_after_code_block_open.py

@@ -0,0 +1,189 @@
+import random
+
+
+def foo1():
+
+    print("The newline above me should be deleted!")
+
+
+def foo2():
+
+
+
+    print("All the newlines above me should be deleted!")
+
+
+def foo3():
+
+    print("No newline above me!")
+
+    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("The newline above me should be deleted!")
+
+
+for i in range(5):
+
+    print(f"{i}) The line above me should be removed!")
+
+
+for i in range(5):
+
+
+
+    print(f"{i}) The lines above me should be removed!")
+
+
+for i in range(5):
+
+    for j in range(7):
+
+        print(f"{i}) The lines above me should be removed!")
+
+
+if random.randint(0, 3) == 0:
+
+    print("The new line above me is about to be removed!")
+
+
+if random.randint(0, 3) == 0:
+
+
+
+
+    print("The new lines above me is about to be removed!")
+
+
+if random.randint(0, 3) == 0:
+    if random.uniform(0, 1) > 0.5:
+        print("Two lines above me are about to be removed!")
+
+
+while True:
+
+    print("The newline above me should be deleted!")
+
+
+while True:
+
+
+
+    print("The newlines above me should be deleted!")
+
+
+while True:
+
+    while False:
+
+        print("The newlines above me should be deleted!")
+
+
+with open("/path/to/file.txt", mode="w") as file:
+
+    file.write("The new line above me is about to be removed!")
+
+
+with open("/path/to/file.txt", mode="w") as file:
+
+
+
+    file.write("The new lines 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("The newline above me should be deleted!")
+
+
+def foo2():
+    print("All the newlines above me should be deleted!")
+
+
+def foo3():
+    print("No newline above me!")
+
+    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("The newline above me should be deleted!")
+
+
+for i in range(5):
+    print(f"{i}) The line above me should be removed!")
+
+
+for i in range(5):
+    print(f"{i}) The lines above me should be removed!")
+
+
+for i in range(5):
+    for j in range(7):
+        print(f"{i}) The lines above me should be removed!")
+
+
+if random.randint(0, 3) == 0:
+    print("The new line above me is about to be removed!")
+
+
+if random.randint(0, 3) == 0:
+    print("The new lines above me is about to be removed!")
+
+
+if random.randint(0, 3) == 0:
+    if random.uniform(0, 1) > 0.5:
+        print("Two lines above me are about to be removed!")
+
+
+while True:
+    print("The newline above me should be deleted!")
+
+
+while True:
+    print("The newlines above me should be deleted!")
+
+
+while True:
+    while False:
+        print("The newlines above me should be deleted!")
+
+
+with open("/path/to/file.txt", mode="w") as file:
+    file.write("The new line above me is about to be removed!")
+
+
+with open("/path/to/file.txt", mode="w") as file:
+    file.write("The new lines 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/data/preview_310/remove_newline_after match.py

@@ -0,0 +1,34 @@
+def http_status(status):
+
+    match status:
+
+        case 400:
+
+            return "Bad request"
+
+        case 401:
+
+            return "Unauthorized"
+
+        case 403:
+
+            return "Forbidden"
+
+        case 404:
+
+            return "Not found"
+
+# output
+def http_status(status):
+    match status:
+        case 400:
+            return "Bad request"
+
+        case 401:
+            return "Unauthorized"
+
+        case 403:
+            return "Forbidden"
+
+        case 404:
+            return "Not found"

tests/test_black.py

@@ -1461,7 +1461,6 @@ def test_newline_comment_interaction(self) -> None:
         black.assert_stable(source, output, mode=DEFAULT_MODE)
 
     def test_bpo_2142_workaround(self) -> None:
-
         # https://bugs.python.org/issue2142
 
         source, _ = read_data("miscellaneous", "missing_final_newline")

tests/test_format.py

@@ -86,6 +86,13 @@ def test_preview_minimum_python_39_format(filename: str) -> None:
     assert_format(source, expected, mode, minimum_version=(3, 9))
 
 
+@pytest.mark.parametrize("filename", all_data_cases("preview_310"))
+def test_preview_minimum_python_310_format(filename: str) -> None:
+    source, expected = read_data("preview_310", filename)
+    mode = black.Mode(preview=True)
+    assert_format(source, expected, mode, minimum_version=(3, 10))
+
+
 @pytest.mark.parametrize("filename", SOURCES)
 def test_source_is_formatted(filename: str) -> None:
     check_file("", filename, DEFAULT_MODE, data=False)