Formatter: Fix posonlyargs for expr_lambda (#6562)

crates/ruff_python_formatter/resources/test/fixtures/ruff/expression/lambda.py

@@ -91,3 +91,5 @@ lambda *args, b, **kwds,: 0
 lambda *, b, **kwds,: 0
 lambda a, *args, b, **kwds,: 0
 lambda a, *, b, **kwds,: 0
+lambda a, /: a
+lambda a, /, c: a

crates/ruff_python_formatter/src/expression/expr_lambda.rs

@@ -22,7 +22,10 @@ impl FormatNodeRule<ExprLambda> for FormatExprLambda {
 
         write!(f, [text("lambda")])?;
 
-        if !parameters.args.is_empty() || parameters.vararg.is_some() || parameters.kwarg.is_some()
+        if !parameters.args.is_empty()
+            || !parameters.posonlyargs.is_empty()
+            || parameters.vararg.is_some()
+            || parameters.kwarg.is_some()
         {
             write!(
                 f,

crates/ruff_python_formatter/tests/snapshots/black_compatibility@py_38__pep_570.py.snap

@@ -1,168 +0,0 @@
----
-source: crates/ruff_python_formatter/tests/fixtures.rs
-input_file: crates/ruff_python_formatter/resources/test/fixtures/black/py_38/pep_570.py
----
-## Input
-
-```py
-def positional_only_arg(a, /):
-    pass
-
-
-def all_markers(a, b, /, c, d, *, e, f):
-    pass
-
-
-def all_markers_with_args_and_kwargs(
-    a_long_one,
-    b_long_one,
-    /,
-    c_long_one,
-    d_long_one,
-    *args,
-    e_long_one,
-    f_long_one,
-    **kwargs,
-):
-    pass
-
-
-def all_markers_with_defaults(a, b=1, /, c=2, d=3, *, e=4, f=5):
-    pass
-
-
-def long_one_with_long_parameter_names(
-    but_all_of_them,
-    are_positional_only,
-    arguments_mmmmkay,
-    so_this_is_only_valid_after,
-    three_point_eight,
-    /,
-):
-    pass
-
-
-lambda a, /: a
-
-lambda a, b, /, c, d, *, e, f: a
-
-lambda a, b, /, c, d, *args, e, f, **kwargs: args
-
-lambda a, b=1, /, c=2, d=3, *, e=4, f=5: 1
-```
-
-## Black Differences
-
-```diff
---- Black
-+++ Ruff
-@@ -35,7 +35,7 @@
-     pass
- 
- 
--lambda a, /: a
-+lambda: a
- 
- lambda a, b, /, c, d, *, e, f: a
- 
-```
-
-## Ruff Output
-
-```py
-def positional_only_arg(a, /):
-    pass
-
-
-def all_markers(a, b, /, c, d, *, e, f):
-    pass
-
-
-def all_markers_with_args_and_kwargs(
-    a_long_one,
-    b_long_one,
-    /,
-    c_long_one,
-    d_long_one,
-    *args,
-    e_long_one,
-    f_long_one,
-    **kwargs,
-):
-    pass
-
-
-def all_markers_with_defaults(a, b=1, /, c=2, d=3, *, e=4, f=5):
-    pass
-
-
-def long_one_with_long_parameter_names(
-    but_all_of_them,
-    are_positional_only,
-    arguments_mmmmkay,
-    so_this_is_only_valid_after,
-    three_point_eight,
-    /,
-):
-    pass
-
-
-lambda: a
-
-lambda a, b, /, c, d, *, e, f: a
-
-lambda a, b, /, c, d, *args, e, f, **kwargs: args
-
-lambda a, b=1, /, c=2, d=3, *, e=4, f=5: 1
-```
-
-## Black Output
-
-```py
-def positional_only_arg(a, /):
-    pass
-
-
-def all_markers(a, b, /, c, d, *, e, f):
-    pass
-
-
-def all_markers_with_args_and_kwargs(
-    a_long_one,
-    b_long_one,
-    /,
-    c_long_one,
-    d_long_one,
-    *args,
-    e_long_one,
-    f_long_one,
-    **kwargs,
-):
-    pass
-
-
-def all_markers_with_defaults(a, b=1, /, c=2, d=3, *, e=4, f=5):
-    pass
-
-
-def long_one_with_long_parameter_names(
-    but_all_of_them,
-    are_positional_only,
-    arguments_mmmmkay,
-    so_this_is_only_valid_after,
-    three_point_eight,
-    /,
-):
-    pass
-
-
-lambda a, /: a
-
-lambda a, b, /, c, d, *, e, f: a
-
-lambda a, b, /, c, d, *args, e, f, **kwargs: args
-
-lambda a, b=1, /, c=2, d=3, *, e=4, f=5: 1
-```
-
-

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

@@ -97,6 +97,8 @@ lambda *args, b, **kwds,: 0
 lambda *, b, **kwds,: 0
 lambda a, *args, b, **kwds,: 0
 lambda a, *, b, **kwds,: 0
+lambda a, /: a
+lambda a, /, c: a
 ```
 
 ## Output
@@ -195,6 +197,8 @@ lambda *args, b, **kwds,: 0
 lambda *, b, **kwds,: 0
 lambda a, *args, b, **kwds,: 0
 lambda a, *, b, **kwds,: 0
+lambda a, /: a
+lambda a, /, c: a
 ```