Compiler warns to remove parentheses producing invalid code

[fables-tales]

I tried this code:

fn main() {
     for (idx, rt_child) in root.iter_children().enumerate() {
          if let(Some(rt_child)) = rt_child {
            let reply_node = root_child_arena.get_reply_node(rt_child);
            info!("reply_node: {} {:?} {}", Move::from_index(idx), reply_node.get_visits(), reply_node.get_score());
          }
        }
}

I expected to see no compiler warning on the if let(Some(rt_child)) = rt_child line.

Instead, this happened:

warning: unnecessary parentheses around pattern
 --> src/main.rs:3:17
  |
3 |           if let(Some(rt_child)) = rt_child {
  |                 ^              ^
  |
  = note: `#[warn(unused_parens)]` on by default
help: remove these parentheses
  |
3 -           if let(Some(rt_child)) = rt_child {
3 +           if letSome(rt_child) = rt_child {
  |

For more information about this error, try `rustc --explain E0425`.
warning: `playground` (bin "playground") generated 1 warning
error: could not compile `playground` due to 3 previous errors; 1 warning emitted

Meta

here is a rust playground link: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=9d2bfd8156a76f0a565f0caf81b52d80
rustc --version --verbose:

1.64.0

[jruderman]

Simpler:

fn main() {
    if let(Some(_)) = Some(1) {
    }
}

which gives the error-introducing suggestion:

help: remove these parentheses
  |
2 -     if let(Some(_)) = Some(1) {
2 +     if letSome(_) = Some(1) {

[jruderman]

The warning is correct: it is unnecessary to put parens around the entire if let pattern. The suggestion just needs to include a space in this case, so it doesn't run the let and Some tokens together.

The suggestion should be:

help: remove these parentheses
  |
2 -     if let(Some(_)) = Some(1) {
2 +     if let Some(_) = Some(1) {

[jruderman]

@rustbot label +A-diagnostics

[Noratrieb]

@rustbot label D-invalid-suggestion

[chenyukang]

Another case:

fn main() {
    for(_x) in 1..10 { }
}

warning: unnecessary parentheses around pattern
 --> src/main.rs:2:8
  |
2 |     for(_x) in 1..10 { }
  |        ^  ^
  |
  = note: `#[warn(unused_parens)]` on by default
help: remove these parentheses
  |
2 -     for(_x) in 1..10 { }
2 +     for_x in 1..10 { }
  |

I guess we may have some other cases for remove these parentheses

[chenyukang]

@rustbot claim