Improve slice formatting (#5922)

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## Summary

- Remove space when start of slice is empty
- Treat unary op except `not` as simple expression

## Test Plan

Add some simple tests for unary op expressions in slice

Closes #5673

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

@@ -70,12 +70,15 @@ def a():
 e00 = "e"[:]
 e01 = "e"[:1]
 e02 = "e"[: a()]
+e03 = "e"[:-1]
 e10 = "e"[1:]
 e11 = "e"[1:1]
 e12 = "e"[1 : a()]
+e13 = "e"[1:-1]
 e20 = "e"[a() :]
 e21 = "e"[a() : 1]
 e22 = "e"[a() : a()]
+e23 = "e"[a() : -1]
 e200 = "e"[a() :: ]
 e201 = "e"[a() :: 1]
 e202 = "e"[a() :: a()]

crates/ruff_python_formatter/src/expression/expr_slice.rs

@@ -1,6 +1,5 @@
 use ruff_text_size::TextRange;
-use rustpython_parser::ast::ExprSlice;
+use rustpython_parser::ast::{Expr, ExprSlice, ExprUnaryOp, Ranged, UnaryOp};
-use rustpython_parser::ast::{Expr, Ranged};
 
 use ruff_formatter::prelude::{hard_line_break, line_suffix_boundary, space, text};
 use ruff_formatter::{write, Buffer, Format, FormatError, FormatResult};
@@ -87,7 +86,7 @@ impl FormatNodeRule<ExprSlice> for FormatExprSlice {
         // e201 = "e"[a() :: 1]
         // e202 = "e"[a() :: a()]
         // ```
-        if !all_simple {
+        if !all_simple && lower.is_some() {
             space().fmt(f)?;
         }
         text(":").fmt(f)?;
@@ -196,7 +195,17 @@ pub(crate) fn find_colons(
 /// Determines whether this expression needs a space around the colon
 /// <https://black.readthedocs.io/en/stable/the_black_code_style/current_style.html#slices>
 fn is_simple_expr(expr: &Expr) -> bool {
-    matches!(expr, Expr::Constant(_) | Expr::Name(_))
+    // Unary op expressions except `not` can be simple.
+    if let Some(ExprUnaryOp {
+        op: UnaryOp::UAdd | UnaryOp::USub | UnaryOp::Invert,
+        operand,
+        ..
+    }) = expr.as_unary_op_expr()
+    {
+        is_simple_expr(operand)
+    } else {
+        matches!(expr, Expr::Constant(_) | Expr::Name(_))
+    }
 }
 
 pub(crate) enum ExprSliceCommentSection {

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

@@ -323,32 +323,6 @@ last_call()
  )  # note: no trailing comma pre-3.6
  call(*gidgets[:2])
  call(a, *gidgets[:2])
-@@ -152,13 +159,13 @@
- slice[0:1]
- slice[0:1:2]
- slice[:]
--slice[:-1]
-+slice[ : -1]
- slice[1:]
--slice[::-1]
-+slice[ :: -1]
- slice[d :: d + 1]
- slice[:c, c - 1]
- numpy[:, 0:1]
--numpy[:, :-1]
-+numpy[:,  : -1]
- numpy[0, :]
- numpy[:, i]
- numpy[0, :2]
-@@ -172,7 +179,7 @@
- numpy[1 : c + 1, c]
- numpy[-(c + 1) :, d]
- numpy[:, l[-2]]
--numpy[:, ::-1]
-+numpy[:,  :: -1]
- numpy[np.newaxis, :]
- (str or None) if (sys.version_info[0] > (3,)) else (str or bytes or None)
- {"2.7": dead, "3.7": long_live or die_hard}
 @@ -207,25 +214,15 @@
  )
  what_is_up_with_those_new_coord_names = (coord_names | set(vars_to_create)) - set(
@@ -596,13 +570,13 @@ slice[0]
 slice[0:1]
 slice[0:1:2]
 slice[:]
-slice[ : -1]
+slice[:-1]
 slice[1:]
-slice[ :: -1]
+slice[::-1]
 slice[d :: d + 1]
 slice[:c, c - 1]
 numpy[:, 0:1]
-numpy[:,  : -1]
+numpy[:, :-1]
 numpy[0, :]
 numpy[:, i]
 numpy[0, :2]
@@ -616,7 +590,7 @@ numpy[:, [i]]
 numpy[1 : c + 1, c]
 numpy[-(c + 1) :, d]
 numpy[:, l[-2]]
-numpy[:,  :: -1]
+numpy[:, ::-1]
 numpy[np.newaxis, :]
 (str or None) if (sys.version_info[0] > (3,)) else (str or bytes or None)
 {"2.7": dead, "3.7": long_live or die_hard}

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

@@ -211,7 +211,7 @@ d={'a':1,
  # Comment 1
  
  # Comment 2
-@@ -17,30 +16,44 @@
+@@ -17,26 +16,40 @@
  
  # fmt: off
  def func_no_args():
@@ -264,17 +264,12 @@ d={'a':1,
 +    debug: bool = False,
 +    **kwargs,
 +) -> str:
-+    return text[number : -1]
++    return text[number:-1]
 +
 +
  # fmt: on
  def spaces(a=1, b=(), c=[], d={}, e=True, f=-1, g=1 if False else 2, h="", i=r""):
      offset = attr.ib(default=attr.Factory(lambda: _r.uniform(1, 2)))
--    assert task._cancel_stack[: len(old_stack)] == old_stack
-+    assert task._cancel_stack[ : len(old_stack)] == old_stack
- 
- 
- def spaces_types(
 @@ -63,15 +76,15 @@
  
  something = {
@@ -445,13 +440,13 @@ def function_signature_stress_test(
     debug: bool = False,
     **kwargs,
 ) -> str:
-    return text[number : -1]
+    return text[number:-1]
 
 
 # fmt: on
 def spaces(a=1, b=(), c=[], d={}, e=True, f=-1, g=1 if False else 2, h="", i=r""):
     offset = attr.ib(default=attr.Factory(lambda: _r.uniform(1, 2)))
-    assert task._cancel_stack[ : len(old_stack)] == old_stack
+    assert task._cancel_stack[: len(old_stack)] == old_stack
 
 
 def spaces_types(

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

@@ -117,21 +117,6 @@ def __await__(): return (yield)
  
  
  def func_no_args():
-@@ -41,12 +40,12 @@
-     debug: bool = False,
-     **kwargs,
- ) -> str:
--    return text[number:-1]
-+    return text[number : -1]
- 
- 
- def spaces(a=1, b=(), c=[], d={}, e=True, f=-1, g=1 if False else 2, h="", i=r""):
-     offset = attr.ib(default=attr.Factory(lambda: _r.uniform(10000, 200000)))
--    assert task._cancel_stack[: len(old_stack)] == old_stack
-+    assert task._cancel_stack[ : len(old_stack)] == old_stack
- 
- 
- def spaces_types(
 @@ -65,18 +64,14 @@
  
  def spaces2(result=_core.Value(None)):
@@ -220,12 +205,12 @@ def function_signature_stress_test(
     debug: bool = False,
     **kwargs,
 ) -> str:
-    return text[number : -1]
+    return text[number:-1]
 
 
 def spaces(a=1, b=(), c=[], d={}, e=True, f=-1, g=1 if False else 2, h="", i=r""):
     offset = attr.ib(default=attr.Factory(lambda: _r.uniform(10000, 200000)))
-    assert task._cancel_stack[ : len(old_stack)] == old_stack
+    assert task._cancel_stack[: len(old_stack)] == old_stack
 
 
 def spaces_types(

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

@@ -1,151 +0,0 @@
----
-source: crates/ruff_python_formatter/tests/fixtures.rs
-input_file: crates/ruff_python_formatter/resources/test/fixtures/black/simple_cases/slices.py
----
-## Input
-
-```py
-slice[a.b : c.d]
-slice[d :: d + 1]
-slice[d + 1 :: d]
-slice[d::d]
-slice[0]
-slice[-1]
-slice[:-1]
-slice[::-1]
-slice[:c, c - 1]
-slice[c, c + 1, d::]
-slice[ham[c::d] :: 1]
-slice[ham[cheese**2 : -1] : 1 : 1, ham[1:2]]
-slice[:-1:]
-slice[lambda: None : lambda: None]
-slice[lambda x, y, *args, really=2, **kwargs: None :, None::]
-slice[1 or 2 : True and False]
-slice[not so_simple : 1 < val <= 10]
-slice[(1 for i in range(42)) : x]
-slice[:: [i for i in range(42)]]
-
-
-async def f():
-    slice[await x : [i async for i in arange(42)] : 42]
-
-
-# These are from PEP-8:
-ham[1:9], ham[1:9:3], ham[:9:3], ham[1::3], ham[1:9:]
-ham[lower:upper], ham[lower:upper:], ham[lower::step]
-# ham[lower+offset : upper+offset]
-ham[: upper_fn(x) : step_fn(x)], ham[:: step_fn(x)]
-ham[lower + offset : upper + offset]
-```
-
-## Black Differences
-
-```diff
---- Black
-+++ Ruff
-@@ -4,19 +4,19 @@
- slice[d::d]
- slice[0]
- slice[-1]
--slice[:-1]
--slice[::-1]
-+slice[ : -1]
-+slice[ :: -1]
- slice[:c, c - 1]
- slice[c, c + 1, d::]
- slice[ham[c::d] :: 1]
- slice[ham[cheese**2 : -1] : 1 : 1, ham[1:2]]
--slice[:-1:]
-+slice[ : -1 :]
- slice[lambda: None : lambda: None]
- slice[lambda x, y, *args, really=2, **kwargs: None :, None::]
- slice[1 or 2 : True and False]
- slice[not so_simple : 1 < val <= 10]
- slice[(1 for i in range(42)) : x]
--slice[:: [i for i in range(42)]]
-+slice[ :: [i for i in range(42)]]
- 
- 
- async def f():
-@@ -27,5 +27,5 @@
- ham[1:9], ham[1:9:3], ham[:9:3], ham[1::3], ham[1:9:]
- ham[lower:upper], ham[lower:upper:], ham[lower::step]
- # ham[lower+offset : upper+offset]
--ham[: upper_fn(x) : step_fn(x)], ham[:: step_fn(x)]
-+ham[ : upper_fn(x) : step_fn(x)], ham[ :: step_fn(x)]
- ham[lower + offset : upper + offset]
-```
-
-## Ruff Output
-
-```py
-slice[a.b : c.d]
-slice[d :: d + 1]
-slice[d + 1 :: d]
-slice[d::d]
-slice[0]
-slice[-1]
-slice[ : -1]
-slice[ :: -1]
-slice[:c, c - 1]
-slice[c, c + 1, d::]
-slice[ham[c::d] :: 1]
-slice[ham[cheese**2 : -1] : 1 : 1, ham[1:2]]
-slice[ : -1 :]
-slice[lambda: None : lambda: None]
-slice[lambda x, y, *args, really=2, **kwargs: None :, None::]
-slice[1 or 2 : True and False]
-slice[not so_simple : 1 < val <= 10]
-slice[(1 for i in range(42)) : x]
-slice[ :: [i for i in range(42)]]
-
-
-async def f():
-    slice[await x : [i async for i in arange(42)] : 42]
-
-
-# These are from PEP-8:
-ham[1:9], ham[1:9:3], ham[:9:3], ham[1::3], ham[1:9:]
-ham[lower:upper], ham[lower:upper:], ham[lower::step]
-# ham[lower+offset : upper+offset]
-ham[ : upper_fn(x) : step_fn(x)], ham[ :: step_fn(x)]
-ham[lower + offset : upper + offset]
-```
-
-## Black Output
-
-```py
-slice[a.b : c.d]
-slice[d :: d + 1]
-slice[d + 1 :: d]
-slice[d::d]
-slice[0]
-slice[-1]
-slice[:-1]
-slice[::-1]
-slice[:c, c - 1]
-slice[c, c + 1, d::]
-slice[ham[c::d] :: 1]
-slice[ham[cheese**2 : -1] : 1 : 1, ham[1:2]]
-slice[:-1:]
-slice[lambda: None : lambda: None]
-slice[lambda x, y, *args, really=2, **kwargs: None :, None::]
-slice[1 or 2 : True and False]
-slice[not so_simple : 1 < val <= 10]
-slice[(1 for i in range(42)) : x]
-slice[:: [i for i in range(42)]]
-
-
-async def f():
-    slice[await x : [i async for i in arange(42)] : 42]
-
-
-# These are from PEP-8:
-ham[1:9], ham[1:9:3], ham[:9:3], ham[1::3], ham[1:9:]
-ham[lower:upper], ham[lower:upper:], ham[lower::step]
-# ham[lower+offset : upper+offset]
-ham[: upper_fn(x) : step_fn(x)], ham[:: step_fn(x)]
-ham[lower + offset : upper + offset]
-```
-
-

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

@@ -76,12 +76,15 @@ def a():
 e00 = "e"[:]
 e01 = "e"[:1]
 e02 = "e"[: a()]
+e03 = "e"[:-1]
 e10 = "e"[1:]
 e11 = "e"[1:1]
 e12 = "e"[1 : a()]
+e13 = "e"[1:-1]
 e20 = "e"[a() :]
 e21 = "e"[a() : 1]
 e22 = "e"[a() : a()]
+e23 = "e"[a() : -1]
 e200 = "e"[a() :: ]
 e201 = "e"[a() :: 1]
 e202 = "e"[a() :: a()]
@@ -167,13 +170,16 @@ def a():
 
 e00 = "e"[:]
 e01 = "e"[:1]
-e02 = "e"[ : a()]
+e02 = "e"[: a()]
+e03 = "e"[:-1]
 e10 = "e"[1:]
 e11 = "e"[1:1]
 e12 = "e"[1 : a()]
+e13 = "e"[1:-1]
 e20 = "e"[a() :]
 e21 = "e"[a() : 1]
 e22 = "e"[a() : a()]
+e23 = "e"[a() : -1]
 e200 = "e"[a() : :]
 e201 = "e"[a() :: 1]
 e202 = "e"[a() :: a()]