fix: unnecessary_cast suggests extra brackets when in macro

Author: profetia

clippy_lints/src/casts/unnecessary_cast.rs

@@ -150,27 +150,18 @@ pub(super) fn check<'tcx>(
             return false;
         }
 
-        // If the whole cast expression is a unary expression (`(*x as T)`) or an addressof
-        // expression (`(&x as T)`), then not surrounding the suggestion into a block risks us
-        // changing the precedence of operators if the cast expression is followed by an operation
-        // with higher precedence than the unary operator (`(*x as T).foo()` would become
-        // `*x.foo()`, which changes what the `*` applies on).
-        // The same is true if the expression encompassing the cast expression is a unary
-        // expression or an addressof expression.
-        let needs_block = matches!(cast_expr.kind, ExprKind::Unary(..) | ExprKind::AddrOf(..))
-            || get_parent_expr(cx, expr).is_some_and(|e| matches!(e.kind, ExprKind::Unary(..) | ExprKind::AddrOf(..)));
+        let need_paren = matches!(
+            cx.tcx.parent_hir_node(expr.hir_id),
+            Node::Expr(parent) if cast_expr.precedence() < parent.precedence()
+        );
 
         span_lint_and_sugg(
             cx,
             UNNECESSARY_CAST,
             expr.span,
             format!("casting to the same type is unnecessary (`{cast_from}` -> `{cast_to}`)"),
             "try",
-            if needs_block {
-                format!("{{ {cast_str} }}")
-            } else {
-                cast_str
-            },
+            if need_paren { format!("({cast_str})") } else { cast_str },
             Applicability::MachineApplicable,
         );
         return true;

tests/ui/unnecessary_cast.fixed

@@ -224,7 +224,7 @@ mod fixable {
         let _ = &1 as &I32Alias;
 
         let x = 1i32;
-        let _ = &{ x };
+        let _ = &x;
         //~^ unnecessary_cast
     }
 
@@ -266,7 +266,21 @@ mod fixable {
     // Issue #11968: The suggestion for this lint removes the parentheses and leave the code as
     // `*x.pow(2)` which tries to dereference the return value rather than `x`.
     fn issue_11968(x: &usize) -> usize {
-        { *x }.pow(2)
+        (*x).pow(2)
+        //~^ unnecessary_cast
+    }
+
+    #[allow(clippy::cast_lossless)]
+    fn issue_14640() {
+        let x = 5usize;
+        let vec: Vec<u64> = vec![1, 2, 3, 4, 5];
+        assert_eq!(vec.len(), x);
+        //~^ unnecessary_cast
+
+        let _ = (5i32 as i64).abs();
+        //~^ unnecessary_cast
+
+        let _ = 5i32 as i64;
         //~^ unnecessary_cast
     }
 }

tests/ui/unnecessary_cast.rs

@@ -269,4 +269,18 @@ mod fixable {
         (*x as usize).pow(2)
         //~^ unnecessary_cast
     }
+
+    #[allow(clippy::cast_lossless)]
+    fn issue_14640() {
+        let x = 5usize;
+        let vec: Vec<u64> = vec![1, 2, 3, 4, 5];
+        assert_eq!(vec.len(), x as usize);
+        //~^ unnecessary_cast
+
+        let _ = (5i32 as i64 as i64).abs();
+        //~^ unnecessary_cast
+
+        let _ = 5i32 as i64 as i64;
+        //~^ unnecessary_cast
+    }
 }

tests/ui/unnecessary_cast.stderr

@@ -209,7 +209,7 @@ error: casting to the same type is unnecessary (`i32` -> `i32`)
   --> tests/ui/unnecessary_cast.rs:227:18
    |
 LL |         let _ = &(x as i32);
-   |                  ^^^^^^^^^^ help: try: `{ x }`
+   |                  ^^^^^^^^^^ help: try: `x`
 
 error: casting integer literal to `i32` is unnecessary
   --> tests/ui/unnecessary_cast.rs:234:22
@@ -245,7 +245,25 @@ error: casting to the same type is unnecessary (`usize` -> `usize`)
   --> tests/ui/unnecessary_cast.rs:269:9
    |
 LL |         (*x as usize).pow(2)
-   |         ^^^^^^^^^^^^^ help: try: `{ *x }`
+   |         ^^^^^^^^^^^^^ help: try: `(*x)`
 
-error: aborting due to 41 previous errors
+error: casting to the same type is unnecessary (`usize` -> `usize`)
+  --> tests/ui/unnecessary_cast.rs:277:31
+   |
+LL |         assert_eq!(vec.len(), x as usize);
+   |                               ^^^^^^^^^^ help: try: `x`
+
+error: casting to the same type is unnecessary (`i64` -> `i64`)
+  --> tests/ui/unnecessary_cast.rs:280:17
+   |
+LL |         let _ = (5i32 as i64 as i64).abs();
+   |                 ^^^^^^^^^^^^^^^^^^^^ help: try: `(5i32 as i64)`
+
+error: casting to the same type is unnecessary (`i64` -> `i64`)
+  --> tests/ui/unnecessary_cast.rs:283:17
+   |
+LL |         let _ = 5i32 as i64 as i64;
+   |                 ^^^^^^^^^^^^^^^^^^ help: try: `5i32 as i64`
+
+error: aborting due to 44 previous errors