ICE: impossible struct constructor

[petertodd]

Example:

pub struct Foo {}

impl Foo {
    fn bar(Self(foo): Self) {
    }   
}

fn main() {
}

Backtrace:

$ rustc impossible-struct-constructor.rs 
error: internal compiler error: src/librustc/hir/def.rs:316: impossible struct constructor

thread 'main' panicked at 'Box<Any>', src/librustc_errors/lib.rs:600:9
note: Run with `RUST_BACKTRACE=1` for a backtrace.
error: aborting due to previous error


note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.32.0-nightly (f4a421ee3 2018-12-13) running on x86_64-unknown-linux-gnu

[Centril]

Seems related to #56611; ideally we should beta backport the fix to this as well as #56611.

[alexreg]

Already fixed in #56225, I'm glad to say. I've gone and added a regression test for this issue however. It's due to be r+'ed soon, with any luck.