type_id is not crate-independent with object associated types

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$ rustc -V
rustc 1.12.0-dev (5556554e2 2016-07-31)

STR

#![feature(core_intrinsics, rustc_private)]

#[cfg(arena_first)]
extern crate arena;
extern crate term;
#[cfg(not(arena_first))]
extern crate arena;

use std::intrinsics::type_id;

fn main() { unsafe {
    println!("same={:?} different={:?}",
        type_id::<arena::TypedArena<()>>(),
        type_id::<Iterator<Item=arena::TypedArena<()>>>()
    );
}}  

Any pair of crates, one of them with a struct, can be used instead of arena/term.

Expected Result

The Type ID of Iterator<Item=arena::TypedArena<()>> should be the same when the cfg is toggled.

Actual Result

The Type ID of Iterator<Item=arena::TypedArena<()>> differs when the cfg is toggled, but the id of arena::TypedArena<()> does not

1. This is probably the same underlying issue that has been solved for tyencode in https://github.com/rust-lang/rust/pull/34805. Projection bounds should be hashed in deterministic order.

   Michael Woerister at 2016-08-01 08:05:55

2. This should be fixed - projections are now sorted by their DefPath.

   Ariel Ben-Yehuda at 2016-12-25 17:48:22

3. Is this issue still up to date?

   TornaxO7 at 2023-03-10 21:06:38

4. I've tested this with some more modern Rust code:

   #![feature(core_intrinsics, rustc_private)]                                                                                   
   
   use term;
   #[cfg(arena_first)]
   use typed_arena;
   #[cfg(not(arena_first))]
   use typed_arena;
   
   use std::intrinsics::type_id;
    
    fn main() {
        println!(
            "same={:?} different={:?}",
            type_id::<typed_arena::Arena<()>>(),
            type_id::<dyn Iterator<Item = typed_arena::Arena<()>>>()
        );
    }
   

   the Type IDs are now the same compiling with or without --features arena_first, ex:

   $ cargo run --features arena_first
   same=183576685912587470318627960423020482748 different=30593087131907206016297065634067928062
   $ cargo run
   same=183576685912587470318627960423020482748 different=30593087131907206016297065634067928062
   

   apiraino at 2023-07-17 11:25:55

5. reopen as it needs a test, possibly reducing to no external dependencies

   apiraino at 2023-07-25 14:36:56

6. This has an MCVE, just needs test (and there is an open PR).

   Jack Huey at 2023-12-25 00:58:31