Duplicate argument names allowed in extern function declarations

[bjorn3]

I tried this code:

extern "C" {
    fn foo(a: u8, a: u8);
}

I expected to see this happen: Error as there are two arguments named a.

Instead, this happened: Compiles fine.

I found this issue while working on parsing the core_arch and generating code from it. It has the following declaration: fn vcvtss2sd(a: f64x2, a: f32x4, src: f64x2, mask: u8, sae: i32) -> f64x2;.

Meta

Happens with both 1.78 stable and 1.80.0-nightly (2024-05-31 ada5e2c).

[petrochenkov]

This is a duplicate of this old issue - #33995.
I'm still not sure if this is worth changing.

[saethlin]

Closing as duplicate