Compiler error for if/let chaining when not using it inside a map closure syntax error

[tlockhart1996]

Code

fn main() {
    vec![].into_iter().map({ |x| 
        let y = x;
        y
    })
}

Current output

error[E0658]: `let` expressions in this position are unstable

Desired output

Something related to 
`map({ |x|` is a syntax error and should be `map(|x| {`

Rationale and extra context

N/A

Other cases

No response

Anything else?

No response

[estebank]

After #116645:

error: expected expression, found `let` statement
  --> $DIR/ruby_style_closure_parse_error.rs:4:9
   |
LL |     let _ = vec![1, 2, 3].into_iter().map({|x| 
   |                                            --- while parsing the body of this closure
LL |         let y = x;
   |         ^^^
   |
   = note: only supported directly in conditions of `if` and `while` expressions
help: you might have meant to open the body of the closure, instead of enclosing the closure in a block
   |
LL -     let _ = vec![1, 2, 3].into_iter().map({|x| 
LL +     let _ = vec![1, 2, 3].into_iter().map(|x| {