Fix wrong suggestion for `single_element_loop` where parens were missing

clippy_lints/src/loops/single_element_loop.rs

@@ -5,7 +5,7 @@ use clippy_utils::visitors::contains_break_or_continue;
 use rustc_ast::util::parser::PREC_PREFIX;
 use rustc_ast::Mutability;
 use rustc_errors::Applicability;
-use rustc_hir::{is_range_literal, BorrowKind, Expr, ExprKind, Pat};
+use rustc_hir::{is_range_literal, BorrowKind, Expr, ExprKind, Pat, PatKind};
 use rustc_lint::LateContext;
 use rustc_span::edition::Edition;
 use rustc_span::sym;
@@ -70,7 +70,10 @@ pub(super) fn check<'tcx>(
         && !contains_break_or_continue(body)
     {
         let mut applicability = Applicability::MachineApplicable;
-        let pat_snip = snippet_with_applicability(cx, pat.span, "..", &mut applicability);
+        let mut pat_snip = snippet_with_applicability(cx, pat.span, "..", &mut applicability);
+        if matches!(pat.kind, PatKind::Or(..)) {
+            pat_snip = format!("({pat_snip})").into();
+        }
         let mut arg_snip = snippet_with_applicability(cx, arg_expression.span, "..", &mut applicability);
         let mut block_str = snippet_with_applicability(cx, block.span, "..", &mut applicability).into_owned();
         block_str.remove(0);

tests/ui/single_element_loop.fixed

@@ -57,4 +57,12 @@ fn main() {
             }
         };
     }
+
+    // Should lint with correct suggestion (issue #12782)
+    let res_void: Result<bool, bool> = Ok(true);
+
+    {
+        let (Ok(mut _x) | Err(mut _x)) = res_void;
+        let ptr: *const bool = std::ptr::null();
+    }
 }

tests/ui/single_element_loop.rs

@@ -54,4 +54,11 @@ fn main() {
             }
         };
     }
+
+    // Should lint with correct suggestion (issue #12782)
+    let res_void: Result<bool, bool> = Ok(true);
+
+    for (Ok(mut _x) | Err(mut _x)) in [res_void] {
+        let ptr: *const bool = std::ptr::null();
+    }
 }

tests/ui/single_element_loop.stderr

@@ -83,5 +83,21 @@ LL +         };
 LL +     }
    |
 
-error: aborting due to 7 previous errors
+error: for loop over a single element
+  --> tests/ui/single_element_loop.rs:61:5
+   |
+LL | /     for (Ok(mut _x) | Err(mut _x)) in [res_void] {
+LL | |         let ptr: *const bool = std::ptr::null();
+LL | |     }
+   | |_____^
+   |
+help: try
+   |
+LL ~     {
+LL +         let (Ok(mut _x) | Err(mut _x)) = res_void;
+LL +         let ptr: *const bool = std::ptr::null();
+LL +     }
+   |
+
+error: aborting due to 8 previous errors