Inappropriate `warning: unreachable expression` in `println!`

[mizdra]

return expression in call params of println! macro causes inappropriate warning message.

I tried this code (ref: Playground):

fn func1() {
    assert_eq!((), return ());
}

fn func2() {
    println!("{}", return ());
}

fn main() {
    func1();
    func2();
}

I expected to print ^^^ against an entire statement:

warning: unreachable expression
 --> src/main.rs:2:5
  |
2 |     assert_eq!((), return ());
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: #[warn(unreachable_code)] on by default
  = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

warning: unreachable expression
 --> src/main.rs:2:5
  |
2 |     assert_eq!((), return ());
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

warning: unreachable expression
 --> src/main.rs:6:20
  |
6 |     println!("{}", return ());
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^

But, it was printed against an expression instead of a sentence:

warning: unreachable expression
 --> src/main.rs:2:5
  |
2 |     assert_eq!((), return ());
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: #[warn(unreachable_code)] on by default
  = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

warning: unreachable expression
 --> src/main.rs:2:5
  |
2 |     assert_eq!((), return ());
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

warning: unreachable expression
 --> src/main.rs:6:20
  |
6 |     println!("{}", return ());
  |                    ^^^^^^^^^

Meta

rustc --version --verbose: 1.31.1

[estebank]

Current output:

warning: unreachable expression
 --> src/main.rs:2:5
  |
2 |     assert_eq!((), return ());
  |     ^^^^^^^^^^^^^^^---------^^
  |     |              |
  |     |              any code following this expression is unreachable
  |     unreachable expression
  |
  = note: `#[warn(unreachable_code)]` on by default
  = note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

warning: unreachable expression
 --> src/main.rs:2:5
  |
2 |     assert_eq!((), return ());
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
  |     |
  |     unreachable expression
  |     any code following this expression is unreachable
  |
  = note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

warning: unreachable expression
 --> src/main.rs:2:5
  |
2 |     assert_eq!((), return ());
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
  |     |
  |     unreachable expression
  |     any code following this expression is unreachable
  |
  = note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

warning: unreachable expression
 --> src/main.rs:6:20
  |
6 |     println!("{}", return ());
  |                    ^^^^^^^^^
  |                    |
  |                    unreachable expression
  |                    any code following this expression is unreachable