Wrap RUF020 target for multiline fixes

crates/ruff_linter/resources/test/fixtures/ruff/RUF020.py

@@ -21,4 +21,16 @@ def func() -> (
         Never  # text
         | # text
         int
-): ...
+): ...
+
+
+# Regression test for https://github.com/astral-sh/ruff/issues/23207
+# Multi-line single-remaining-element Union should be wrapped in parentheses
+from typing import Literal
+
+x: Union[
+    Never,
+    Literal["LongLiteralNumberOne"]
+    | Literal["LongLiteralNumberTwo"]
+    | Literal["LongLiteralNumberThree"]
+]

crates/ruff_linter/src/rules/ruff/rules/never_union.rs

@@ -2,6 +2,7 @@ use ruff_diagnostics::Applicability;
 use ruff_macros::{ViolationMetadata, derive_message_formats};
 use ruff_python_ast::{self as ast, Expr, ExprBinOp, Operator};
 use ruff_python_semantic::{SemanticModel, analyze::typing::traverse_union};
+use ruff_source_file::LineRanges;
 use ruff_text_size::{Ranged, TextRange};
 
 use crate::checkers::ast::Checker;
@@ -172,7 +173,12 @@ pub(crate) fn never_union(checker: &Checker, expr: &Expr) {
                         Edit::range_replacement(
                             if let [only] = rest.as_slice() {
                                 // Ex) `typing.Union[typing.NoReturn, int]` -> `int`
-                                checker.locator().slice(only).to_string()
+                                let inner = checker.locator().slice(only);
+                                if checker.locator().contains_line_break(only.range()) {
+                                    format!("({inner})")
+                                } else {
+                                    inner.to_string()
+                                }
                             } else {
                                 // Ex) `typing.Union[typing.NoReturn, int, str]` -> `typing.Union[int, str]`
                                 checker

crates/ruff_linter/src/rules/ruff/snapshots/ruff_linter__rules__ruff__tests__RUF020_RUF020.py.snap

@@ -215,4 +215,27 @@ help: Remove `Never`
    -         | # text
 21 |         int
 22 | ): ...
+23 | 
 note: This is an unsafe fix and may change runtime behavior
+
+RUF020 [*] `Union[Never, T]` is equivalent to `T`
+  --> RUF020.py:32:5
+   |
+31 | x: Union[
+32 |     Never,
+   |     ^^^^^
+33 |     Literal["LongLiteralNumberOne"]
+34 |     | Literal["LongLiteralNumberTwo"]
+   |
+help: Remove `Never`
+28 | # Multi-line single-remaining-element Union should be wrapped in parentheses
+29 | from typing import Literal
+30 | 
+   - x: Union[
+   -     Never,
+   -     Literal["LongLiteralNumberOne"]
+31 + x: (Literal["LongLiteralNumberOne"]
+32 |     | Literal["LongLiteralNumberTwo"]
+   -     | Literal["LongLiteralNumberThree"]
+   - ]
+33 +     | Literal["LongLiteralNumberThree"])