Wrap UP007 target for multiline fixes (#23208)

## Summary

Closes #23207.

Author: charliermarsh

crates/ruff_linter/resources/test/fixtures/pyupgrade/UP007.py

@@ -139,3 +139,17 @@ def myfunc(param: "tuple[Union[int, 'AClass', None], str]"):
 b_string_te_2: "UnionTE[NamedTupleTE, None]" = None
 b_string_typing_1: "typing.Union[typing.NamedTuple]" = None
 b_string_typing_2: "typing.Union[typing.NamedTuple, None]" = None
+
+
+# Regression test for https://github.com/astral-sh/ruff/issues/23207
+# Multi-line single-argument Union should be wrapped in parentheses
+from __future__ import annotations
+
+if TYPE_CHECKING:
+    from typing import Literal, TypeAlias
+
+    LongLiterals: TypeAlias = Union[
+        Literal["LongLiteralNumberOne"]
+        | Literal["LongLiteralNumberTwo"]
+        | Literal["LongLiteralNumberThree"]
+    ]

crates/ruff_linter/src/rules/pyupgrade/rules/use_pep604_annotation.rs

@@ -3,6 +3,7 @@ use ruff_python_ast::PythonVersion;
 use ruff_python_ast::helpers::{pep_604_optional, pep_604_union};
 use ruff_python_ast::{self as ast, Expr};
 use ruff_python_semantic::analyze::typing::{Pep604Operator, to_pep604_operator};
+use ruff_source_file::LineRanges;
 use ruff_text_size::Ranged;
 
 use crate::checkers::ast::Checker;
@@ -230,13 +231,19 @@ pub(crate) fn non_pep604_annotation(
                     }
                     _ => {
                         // Single argument.
+                        let inner = checker.locator().slice(slice);
+                        let content = if checker.locator().contains_line_break(slice.range()) {
+                            // If the inner expression spans multiple lines, wrap in
+                            // parentheses since the `Union[...]` brackets that
+                            // previously provided implicit line continuation are being
+                            // removed.
+                            format!("({inner})")
+                        } else {
+                            inner.to_string()
+                        };
                         diagnostic.set_fix(Fix::applicable_edit(
                             Edit::range_replacement(
-                                pad(
-                                    checker.locator().slice(slice).to_string(),
-                                    expr.range(),
-                                    checker.locator(),
-                                ),
+                                pad(content, expr.range(), checker.locator()),
                                 expr.range(),
                             ),
                             applicability,

crates/ruff_linter/src/rules/pyupgrade/snapshots/ruff_linter__rules__pyupgrade__tests__UP007.py.snap

@@ -342,4 +342,29 @@ help: Convert to `X | Y`
 91 + def myfunc(param: "tuple[int | 'AClass' | None, str]"):
 92 |     print(param)
 93 | 
-94 |
+94 | 
+
+UP007 [*] Use `X | Y` for type annotations
+   --> UP007.py:151:31
+    |
+149 |       from typing import Literal, TypeAlias
+150 |
+151 |       LongLiterals: TypeAlias = Union[
+    |  _______________________________^
+152 | |         Literal["LongLiteralNumberOne"]
+153 | |         | Literal["LongLiteralNumberTwo"]
+154 | |         | Literal["LongLiteralNumberThree"]
+155 | |     ]
+    | |_____^
+    |
+help: Convert to `X | Y`
+148 | if TYPE_CHECKING:
+149 |     from typing import Literal, TypeAlias
+150 | 
+    -     LongLiterals: TypeAlias = Union[
+    -         Literal["LongLiteralNumberOne"]
+151 +     LongLiterals: TypeAlias = (Literal["LongLiteralNumberOne"]
+152 |         | Literal["LongLiteralNumberTwo"]
+    -         | Literal["LongLiteralNumberThree"]
+    -     ]
+153 +         | Literal["LongLiteralNumberThree"])