Compilation Hang and Memory Exhaustion When Compiling Code with Associated Type and Trait Objects

[iamanonymouscs]

I tried this code:

pub trait Sampler<D> {
    type Iter<'a, F: FnMut(Self::Iter<'_, F>) -> f64>: Iterator<Item = D>
    where
        Self: 'a;
    fn sample<F: FnMut(&D) -> f64>(&self, pdf: F) -> Self::Iter<'_, F>;
}
pub struct Metropolis<D: 'static, S: Sampler<D>>(Vec<D>, S);
impl<D: 'static, S: Sampler<D>> Sampler<Vec<D>> for Metropolis<D, S> {
    type Iter<'a, F: FnMut(&Vec<D>) -> f64>
    where
        S: 'a,
    = impl Iterator<Item = Vec<D>> + 'a;
    fn sample<F: FnMut(&Vec<D>) -> f64>(&self, mut pdf: F) -> Self::Iter<'_, F> {
        || {
            self.1.sample(|_| 0.0);
        };
        std::iter::empty()
    }
}

I expected to see this happen: The compiler compiles successfully or outputs an error message.

Instead, this happened: The Rust compiler hangs indefinitely and exhausts memory during compilation, leading to an abnormal exit (return code 137).

Meta

rustc --version --verbose:

rustc 1.73.0 (cc66ad468 2023-10-03)
binary: rustc
commit-hash: cc66ad468955717ab92600c770da8c1601a4ff33
commit-date: 2023-10-03
host: x86_64-unknown-linux-gnu
release: 1.73.0
LLVM version: 17.0.2

The same problem is reproduced on the nightly version(1.75.0-nightly aa1a71e9e 2023-10-26)

what's more, to get more information,I also tried '-Z time-passes' (using nighly version):

Output

$ rustc code.rs -Z time-passes
time:   0.003; rss:   30MB ->   32MB (   +2MB)	parse_crate
time:   0.001; rss:   33MB ->   34MB (   +1MB)	setup_global_ctxt
time:   0.024; rss:   34MB ->   47MB (  +13MB)	expand_crate
time:   0.024; rss:   34MB ->   47MB (  +13MB)	macro_expand_crate
time:   0.002; rss:   47MB ->   49MB (   +2MB)	finalize_macro_resolutions
time:   0.003; rss:   49MB ->   52MB (   +3MB)	late_resolve_crate
time:   0.006; rss:   47MB ->   52MB (   +5MB)	resolve_crate
error[E0658]: `impl Trait` in associated types is unstable
  --> code.rs:12:7
   |
12 |     = impl Iterator<Item = Vec<D>> + 'a;
   |       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information
   = help: add `#![feature(impl_trait_in_assoc_type)]` to the crate attributes to enable

time:   0.007; rss:   52MB ->   58MB (   +5MB)	complete_gated_feature_checking
warning: where clause not allowed here
  --> code.rs:10:5
   |
10 | /     where
11 | |         S: 'a,
   | |______________^
   |
   = note: see issue #89122 <https://github.com/rust-lang/rust/issues/89122> for more information
   = note: `#[warn(deprecated_where_clause_location)]` on by default
help: move it to the end of the type declaration
   |
10 ~     
11 ~     = impl Iterator<Item = Vec<D>> + 'a where S: 'a;
   |

error[E0601]: `main` function not found in crate `code`
  --> code.rs:19:2
   |
19 | }
   |  ^ consider adding a `main` function to `code.rs`

time:   0.011; rss:   52MB ->   59MB (   +7MB)	looking_for_entry_point
time:   0.013; rss:   52MB ->   59MB (   +7MB)	misc_checking_1
time:   0.006; rss:   59MB ->   63MB (   +4MB)	type_collecting

[krtab]

@rustbot assign @krtab

[rustbot]

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[krtab]

Oops, wrong issue, my bad.
@rustbot unassign