Improve dummy_implementations preview style formatting (#9240)

crates/ruff_python_formatter/resources/test/fixtures/ruff/newlines.py

@@ -253,4 +253,23 @@ if True:
 # empty line(s) at the end of the file due to nested function
 if True:
     def nested_trailing_function():
-        pass
+        pass
+
+
+def overload1(): ...  # trailing comment
+def overload1(a: int): ...
+
+def overload2(): ...  # trailing comment
+
+def overload2(a: int): ...
+
+def overload3():
+    ...
+    # trailing comment
+def overload3(a: int): ...
+
+def overload4():
+    ...
+    # trailing comment
+
+def overload4(a: int): ...

crates/ruff_python_formatter/src/statement/clause.rs

@@ -392,9 +392,13 @@ pub(crate) fn clause_body<'a>(
 
 impl Format<PyFormatContext<'_>> for FormatClauseBody<'_> {
     fn fmt(&self, f: &mut Formatter<PyFormatContext<'_>>) -> FormatResult<()> {
-        // In stable, stubs are only collapsed in stub files, in preview this is consistently
+        // In stable, stubs are only collapsed in stub files, in preview stubs in functions
-        // applied everywhere
+        // or classes are collapsed too
-        if (f.options().source_type().is_stub() || is_dummy_implementations_enabled(f.context()))
+        let should_collapse_stub = f.options().source_type().is_stub()
+            || (is_dummy_implementations_enabled(f.context())
+                && matches!(self.kind, SuiteKind::Function | SuiteKind::Class));
+
+        if should_collapse_stub
             && contains_only_an_ellipsis(self.body, f.context().comments())
             && self.trailing_comments.is_empty()
         {

crates/ruff_python_formatter/src/statement/suite.rs

@@ -12,7 +12,8 @@ use crate::context::{NodeLevel, TopLevelStatementPosition, WithIndentLevel, With
 use crate::expression::expr_string_literal::ExprStringLiteralKind;
 use crate::prelude::*;
 use crate::preview::{
-    is_module_docstring_newlines_enabled, is_no_blank_line_before_class_docstring_enabled,
+    is_dummy_implementations_enabled, is_module_docstring_newlines_enabled,
+    is_no_blank_line_before_class_docstring_enabled,
 };
 use crate::statement::stmt_expr::FormatStmtExpr;
 use crate::verbatim::{
@@ -261,12 +262,31 @@ impl FormatRule<Suite, PyFormatContext<'_>> for FormatSuite {
                         f,
                     )?;
                 } else {
-                    match self.kind {
+                    // Preserve empty lines after a stub implementation but don't insert a new one if there isn't any present in the source.
-                        SuiteKind::TopLevel => {
+                    // This is useful when having multiple function overloads that should be grouped to getter by omitting new lines between them.
-                            write!(f, [empty_line(), empty_line()])?;
+                    let is_preceding_stub_function_without_empty_line =
-                        }
+                        is_dummy_implementations_enabled(f.context())
-                        SuiteKind::Function | SuiteKind::Class | SuiteKind::Other => {
+                            && following.is_function_def_stmt()
-                            empty_line().fmt(f)?;
+                            && preceding
+                                .as_function_def_stmt()
+                                .is_some_and(|preceding_stub| {
+                                    contains_only_an_ellipsis(
+                                        &preceding_stub.body,
+                                        f.context().comments(),
+                                    ) && lines_after_ignoring_end_of_line_trivia(
+                                        preceding_stub.end(),
+                                        f.context().source(),
+                                    ) < 2
+                                });
+
+                    if !is_preceding_stub_function_without_empty_line {
+                        match self.kind {
+                            SuiteKind::TopLevel => {
+                                write!(f, [empty_line(), empty_line()])?;
+                            }
+                            SuiteKind::Function | SuiteKind::Class | SuiteKind::Other => {
+                                empty_line().fmt(f)?;
+                            }
                         }
                     }
                 }

crates/ruff_python_formatter/tests/snapshots/black_compatibility@cases__preview_dummy_implementations.py.snap

@@ -1,276 +0,0 @@
----
-source: crates/ruff_python_formatter/tests/fixtures.rs
-input_file: crates/ruff_python_formatter/resources/test/fixtures/black/cases/preview_dummy_implementations.py
----
-## Input
-
-```python
-from typing import NoReturn, Protocol, Union, overload
-
-class Empty:
-    ...
-
-def dummy(a): ...
-async def other(b): ...
-
-
-@overload
-def a(arg: int) -> int: ...
-@overload
-def a(arg: str) -> str: ...
-@overload
-def a(arg: object) -> NoReturn: ...
-def a(arg: Union[int, str, object]) -> Union[int, str]:
-    if not isinstance(arg, (int, str)):
-        raise TypeError
-    return arg
-
-class Proto(Protocol):
-    def foo(self, a: int) -> int:
-        ...
-
-    def bar(self, b: str) -> str: ...
-    def baz(self, c: bytes) -> str:
-        ...
-
-
-def dummy_two():
-    ...
-@dummy
-def dummy_three():
-    ...
-
-def dummy_four():
-    ...
-
-@overload
-def b(arg: int) -> int: ...
-
-@overload
-def b(arg: str) -> str: ...
-@overload
-def b(arg: object) -> NoReturn: ...
-
-def b(arg: Union[int, str, object]) -> Union[int, str]:
-    if not isinstance(arg, (int, str)):
-        raise TypeError
-    return arg
-
-def has_comment():
-    ...  # still a dummy
-
-if some_condition:
-    ...
-
-if already_dummy: ...
-```
-
-## Black Differences
-
-```diff
---- Black
-+++ Ruff
-@@ -5,15 +5,23 @@
- 
- 
- def dummy(a): ...
-+
-+
- async def other(b): ...
- 
- 
- @overload
- def a(arg: int) -> int: ...
-+
-+
- @overload
- def a(arg: str) -> str: ...
-+
-+
- @overload
- def a(arg: object) -> NoReturn: ...
-+
-+
- def a(arg: Union[int, str, object]) -> Union[int, str]:
-     if not isinstance(arg, (int, str)):
-         raise TypeError
-@@ -24,10 +32,13 @@
-     def foo(self, a: int) -> int: ...
- 
-     def bar(self, b: str) -> str: ...
-+
-     def baz(self, c: bytes) -> str: ...
- 
- 
- def dummy_two(): ...
-+
-+
- @dummy
- def dummy_three(): ...
- 
-@@ -41,6 +52,8 @@
- 
- @overload
- def b(arg: str) -> str: ...
-+
-+
- @overload
- def b(arg: object) -> NoReturn: ...
- 
-@@ -54,8 +67,6 @@
- def has_comment(): ...  # still a dummy
- 
- 
--if some_condition:
--    ...
-+if some_condition: ...
- 
--if already_dummy:
--    ...
-+if already_dummy: ...
-```
-
-## Ruff Output
-
-```python
-from typing import NoReturn, Protocol, Union, overload
-
-
-class Empty: ...
-
-
-def dummy(a): ...
-
-
-async def other(b): ...
-
-
-@overload
-def a(arg: int) -> int: ...
-
-
-@overload
-def a(arg: str) -> str: ...
-
-
-@overload
-def a(arg: object) -> NoReturn: ...
-
-
-def a(arg: Union[int, str, object]) -> Union[int, str]:
-    if not isinstance(arg, (int, str)):
-        raise TypeError
-    return arg
-
-
-class Proto(Protocol):
-    def foo(self, a: int) -> int: ...
-
-    def bar(self, b: str) -> str: ...
-
-    def baz(self, c: bytes) -> str: ...
-
-
-def dummy_two(): ...
-
-
-@dummy
-def dummy_three(): ...
-
-
-def dummy_four(): ...
-
-
-@overload
-def b(arg: int) -> int: ...
-
-
-@overload
-def b(arg: str) -> str: ...
-
-
-@overload
-def b(arg: object) -> NoReturn: ...
-
-
-def b(arg: Union[int, str, object]) -> Union[int, str]:
-    if not isinstance(arg, (int, str)):
-        raise TypeError
-    return arg
-
-
-def has_comment(): ...  # still a dummy
-
-
-if some_condition: ...
-
-if already_dummy: ...
-```
-
-## Black Output
-
-```python
-from typing import NoReturn, Protocol, Union, overload
-
-
-class Empty: ...
-
-
-def dummy(a): ...
-async def other(b): ...
-
-
-@overload
-def a(arg: int) -> int: ...
-@overload
-def a(arg: str) -> str: ...
-@overload
-def a(arg: object) -> NoReturn: ...
-def a(arg: Union[int, str, object]) -> Union[int, str]:
-    if not isinstance(arg, (int, str)):
-        raise TypeError
-    return arg
-
-
-class Proto(Protocol):
-    def foo(self, a: int) -> int: ...
-
-    def bar(self, b: str) -> str: ...
-    def baz(self, c: bytes) -> str: ...
-
-
-def dummy_two(): ...
-@dummy
-def dummy_three(): ...
-
-
-def dummy_four(): ...
-
-
-@overload
-def b(arg: int) -> int: ...
-
-
-@overload
-def b(arg: str) -> str: ...
-@overload
-def b(arg: object) -> NoReturn: ...
-
-
-def b(arg: Union[int, str, object]) -> Union[int, str]:
-    if not isinstance(arg, (int, str)):
-        raise TypeError
-    return arg
-
-
-def has_comment(): ...  # still a dummy
-
-
-if some_condition:
-    ...
-
-if already_dummy:
-    ...
-```
-
-

crates/ruff_python_formatter/tests/snapshots/format@newlines.py.snap

@@ -259,7 +259,27 @@ if True:
 # empty line(s) at the end of the file due to nested function
 if True:
     def nested_trailing_function():
-        pass```
+        pass
+
+
+def overload1(): ...  # trailing comment
+def overload1(a: int): ...
+
+def overload2(): ...  # trailing comment
+
+def overload2(a: int): ...
+
+def overload3():
+    ...
+    # trailing comment
+def overload3(a: int): ...
+
+def overload4():
+    ...
+    # trailing comment
+
+def overload4(a: int): ...
+```
 
 ## Output
 ```python
@@ -546,6 +566,40 @@ if True:
 
     def nested_trailing_function():
         pass
+
+
+def overload1():
+    ...  # trailing comment
+
+
+def overload1(a: int):
+    ...
+
+
+def overload2():
+    ...  # trailing comment
+
+
+def overload2(a: int):
+    ...
+
+
+def overload3():
+    ...
+    # trailing comment
+
+
+def overload3(a: int):
+    ...
+
+
+def overload4():
+    ...
+    # trailing comment
+
+
+def overload4(a: int):
+    ...
 ```
 
 
@@ -569,6 +623,48 @@ if True:
  
  
  def fakehttp():
+@@ -283,20 +281,14 @@
+         pass
+ 
+ 
+-def overload1():
+-    ...  # trailing comment
++def overload1(): ...  # trailing comment
++def overload1(a: int): ...
+ 
+ 
+-def overload1(a: int):
+-    ...
++def overload2(): ...  # trailing comment
+ 
+ 
+-def overload2():
+-    ...  # trailing comment
+-
+-
+-def overload2(a: int):
+-    ...
++def overload2(a: int): ...
+ 
+ 
+ def overload3():
+@@ -304,8 +296,7 @@
+     # trailing comment
+ 
+ 
+-def overload3(a: int):
+-    ...
++def overload3(a: int): ...
+ 
+ 
+ def overload4():
+@@ -313,5 +304,4 @@
+     # trailing comment
+ 
+ 
+-def overload4(a: int):
+-    ...
++def overload4(a: int): ...
 ```
 
 

crates/ruff_python_formatter/tests/snapshots/format@statement__top_level.py.snap

@@ -150,21 +150,23 @@ def quuz():
  
  
  class Baz(Qux):
-@@ -49,12 +44,10 @@
+@@ -49,14 +44,8 @@
          pass
  
  
 -def bar():
 -    ...
-+def bar(): ...
+-
- 
+-
- 
 -def baz():
 -    ...
+-
+-
++def bar(): ...
 +def baz(): ...
- 
- 
  def quux():
+     """Some docstring."""
+ 
 ```