[flake8-pyi] Improve autofix safety for redundant-none-literal (P…

…YI061) (#14583)

Co-authored-by: Alex Waygood <[email protected]>

crates/ruff_linter/resources/test/fixtures/flake8_pyi/PYI061.py

@@ -1,4 +1,4 @@
-from typing import Literal
+from typing import Literal, Union
 
 
 def func1(arg1: Literal[None]):
@@ -17,21 +17,29 @@ def func4(arg1: Literal[int, None, float]):
     ...
 
 
-def func5(arg1: Literal[None, None]): 
+def func5(arg1: Literal[None, None]):
     ...
 
 
 def func6(arg1: Literal[
     "hello",
     None  # Comment 1
     , "world"
-    ]): 
+    ]):
     ...
 
 
 def func7(arg1: Literal[
     None  # Comment 1
-    ]): 
+    ]):
+    ...
+
+
+def func8(arg1: Literal[None] | None):
+    ...
+
+
+def func9(arg1: Union[Literal[None], None]):
     ...
 
 
@@ -58,3 +66,16 @@ def good_func(arg1: Literal[int] | None):
 # and there are no None members in the Literal[] slice,
 # only emit Y062:
 Literal[None, True, None, True]  # Y062 Duplicate "Literal[]" member "True"
+
+
+# Regression tests for https://github.com/astral-sh/ruff/issues/14567
+x: Literal[None] | None
+y: None | Literal[None]
+z: Union[Literal[None], None]
+
+a: int | Literal[None] | None
+b: None | Literal[None] | None
+c: (None | Literal[None]) | None
+d: None | (Literal[None] | None)
+e: None | ((None | Literal[None]) | None) | None
+f: Literal[None] | Literal[None]

crates/ruff_linter/resources/test/fixtures/flake8_pyi/PYI061.pyi

@@ -1,4 +1,4 @@
-from typing import Literal
+from typing import Literal, Union
 
 
 def func1(arg1: Literal[None]): ...
@@ -28,10 +28,29 @@ def func7(arg1: Literal[
 ]): ...
 
 
+def func8(arg1: Literal[None] | None):...
+
+
+def func9(arg1: Union[Literal[None], None]): ...
+
+
 # OK
 def good_func(arg1: Literal[int] | None): ...
 
 
 # From flake8-pyi
 Literal[None]  # PYI061 None inside "Literal[]" expression. Replace with "None"
 Literal[True, None]  # PYI061 None inside "Literal[]" expression. Replace with "Literal[True] | None"
+
+
+# Regression tests for https://github.com/astral-sh/ruff/issues/14567
+x: Literal[None] | None
+y: None | Literal[None]
+z: Union[Literal[None], None]
+
+a: int | Literal[None] | None
+b: None | Literal[None] | None
+c: (None | Literal[None]) | None
+d: None | (Literal[None] | None)
+e: None | ((None | Literal[None]) | None) | None
+f: Literal[None] | Literal[None]

crates/ruff_linter/src/rules/flake8_pyi/rules/redundant_none_literal.rs

@@ -1,7 +1,10 @@
 use ruff_diagnostics::{Applicability, Diagnostic, Edit, Fix, FixAvailability, Violation};
 use ruff_macros::{derive_message_formats, violation};
-use ruff_python_ast::{Expr, ExprNoneLiteral};
-use ruff_python_semantic::analyze::typing::traverse_literal;
+use ruff_python_ast::{Expr, ExprBinOp, ExprNoneLiteral, ExprSubscript, Operator};
+use ruff_python_semantic::{
+    analyze::typing::{traverse_literal, traverse_union},
+    SemanticModel,
+};
 use ruff_text_size::Ranged;
 
 use smallvec::SmallVec;
@@ -31,6 +34,9 @@ use crate::checkers::ast::Checker;
 /// Literal[1, 2, 3, "foo", 5] | None
 /// ```
 ///
+/// ## Fix safety
+/// This rule's fix is marked as safe unless the literal contains comments.
+///
 /// ## References
 /// - [Typing documentation: Legal parameters for `Literal` at type check time](https://typing.readthedocs.io/en/latest/spec/literal.html#legal-parameters-for-literal-at-type-check-time)
 #[violation]
@@ -87,14 +93,16 @@ pub(crate) fn redundant_none_literal<'a>(checker: &mut Checker, literal_expr: &'
     let fix = if other_literal_elements_seen {
         None
     } else {
-        Some(Fix::applicable_edit(
-            Edit::range_replacement("None".to_string(), literal_expr.range()),
-            if checker.comment_ranges().intersects(literal_expr.range()) {
-                Applicability::Unsafe
-            } else {
-                Applicability::Safe
-            },
-        ))
+        create_fix_edit(checker.semantic(), literal_expr).map(|edit| {
+            Fix::applicable_edit(
+                edit,
+                if checker.comment_ranges().intersects(literal_expr.range()) {
+                    Applicability::Unsafe
+                } else {
+                    Applicability::Safe
+                },
+            )
+        })
     };
 
     for none_expr in none_exprs {
@@ -110,3 +118,47 @@ pub(crate) fn redundant_none_literal<'a>(checker: &mut Checker, literal_expr: &'
         checker.diagnostics.push(diagnostic);
     }
 }
+
+fn create_fix_edit(semantic: &SemanticModel, literal_expr: &Expr) -> Option<Edit> {
+    let mut enclosing_union = None;
+    for expr in semantic.current_expressions().skip(1).take_while(|expr| {
+        matches!(
+            expr,
+            Expr::BinOp(ExprBinOp {
+                op: Operator::BitOr,
+                ..
+            })
+        )
+    }) {
+        enclosing_union = Some(expr);
+    }
+
+    let mut is_fixable = true;
+    if let Some(enclosing_union) = enclosing_union {
+        traverse_union(
+            &mut |expr, _| {
+                if matches!(expr, Expr::NoneLiteral(_)) {
+                    is_fixable = false;
+                }
+                if expr != literal_expr {
+                    if let Expr::Subscript(ExprSubscript { value, slice, .. }) = expr {
+                        if semantic.match_typing_expr(value, "Literal")
+                            && matches!(**slice, Expr::NoneLiteral(_))
+                        {
+                            is_fixable = false;
+                        }
+                    }
+                }
+            },
+            semantic,
+            enclosing_union,
+        );
+    }
+
+    // Avoid producing code that would raise an exception when
+    // `Literal[None] | None` would be fixed to `None | None`.
+    // Instead do not provide a fix. No action needed for `typing.Union`,
+    // as `Union[None, None]` is valid Python.
+    // See https://github.com/astral-sh/ruff/issues/14567.
+    is_fixable.then(|| Edit::range_replacement("None".to_string(), literal_expr.range()))
+}