Actually the type system catches that particular mistake:

    error[E0308]: mismatched types
     --> src/main.rs:5:6
      |
    5 |   if x = 1 {
      |      ^^^^^ expected bool, found ()  
      |
      = note: expected type `bool`
      = note:    found type `()`
    
    error: aborting due to previous error
    
    error: Could not compile `playground`.
    
    To learn more, run the command again with --verbose.