postfix_increment show both type of suggestion for single statement

[chenyukang]

Story from here

Given the following code:

fn main() {
    let mut i = 0;
    i++;
    println!("i: {:?}", i);
}

The current output is:

error: Rust has no postfix increment operator
 --> ./p/inc.rs:3:6
  |
3 |     i++;
  |      ^^ not a valid postfix operator
  |
help: use `+= 1` instead
  |
3 |     { let tmp = i; i += 1; tmp };
  |     +++++++++++  ~~~~~~~~~~~~~~~
3 |     i += 1;
  |       ~~~~

Ideally the output should look like:

error: Rust has no postfix increment operator
 --> ./p/inc.rs:3:6
  |
3 |     i++;
  |      ^^ not a valid postfix operator
  |
help: use `+= 1` instead
3 |     i += 1;
  |       ~~~~

[chenyukang]

@rustbot claim

[chenyukang]

Our current suggestion for this code is wrong:

fn test2() {
    let mut i = 0;
    if i++ == 1 {}
}

Current output:

error: Rust has no postfix increment operator
 --> ./p/inc.rs:8:9
  |
8 |     if i++ == 1 {}
  |         ^^ not a valid postfix operator
  |
help: use `+= 1` instead
  |
8 |     if { let tmp = i; i += 1; tmp } == 1 {}
  |        +++++++++++  ~~~~~~~~~~~~~~~
8 |     if i += 1 == 1 {}
  |          ~~~~

The second one is not right.