Wrong "unnecessary parentheses around function argument"-warning with macro in assignment and return positions

[Phlosioneer]

I tried this code:

macro_rules! range_array {
    ( $( $num:tt ),* ) => {
        [ $( { let value = $num; value..=value } ),* ]
    };
}

fn foo(x: u8) -> u8 {
    x
}

fn main() {
    // This isn't allowed, need to use a token tree.
    //assert_eq!(range_array![1, foo(4), 5], [1..=1, 4..=4, 5..=5])

    // But this triggers an unused_paren warning.
    assert_eq!(range_array![1, (foo(4)), 5], [1..=1, 4..=4, 5..=5]);
}

I expected to see this happen: No warnings

Instead, this happened:

warning: unnecessary parentheses around assigned value
  --> src/main.rs:12:32
   |
12 |     assert_eq!(range_array![1, (foo(4)), 5], [1..=1, 4..=4, 5..=5]);
   |                                ^      ^
   |
   = note: `#[warn(unused_parens)]` on by default

This is an unexpected corner case of #47775 (assignment), and was not fixed by #47896. Assignment-expressions and block-return-expressions are affected:

$num; // OK
let value = $num; // Warn
let value = 0 + $num; // OK
let value = 0 + ($num); // OK
let value = { $num }; // Warn
let value = 0 + { $num }; // Warn
let value = { 0 + $num }; // OK
{ $num }; // Warn
0 + { $num }; // Warn

In my actual use case, I can't do 0 + $num. I don't think I have any idenity function available.

Meta

rustc --version --verbose:

rustc 1.72.0-nightly (83964c156 2023-07-08)
binary: rustc
commit-hash: 83964c156db1f444050a38b2498dbd0da6d5d503
commit-date: 2023-07-08
host: x86_64-pc-windows-msvc
release: 1.72.0-nightly
LLVM version: 16.0.5

I still have a 1.36 install of rust, and that showed the same warning, so I think this has been around for a while.

[Noratrieb]

I don't think it's easy to fix this. The lint works on the finalized AST and can't really take into account the details of how the macro was expanded. The easiest solution here is to just put an #[allow()] inside the macro for now (which you've probably done already).