-Zdump-mir introduces cycle in static containing static reference

[dtolnay]

// src/lib.rs

pub struct Thing {
    pub next: &'static Thing,
}

pub static THING: Thing = Thing { next: &THING };

$ cargo clean
$ RUSTFLAGS=-Zdump-mir= cargo build

error[E0391]: cycle detected when evaluating initializer of static `THING`
 --> src/lib.rs:7:1
  |
7 | pub static THING: Thing = Thing { next: &THING };
  | ^^^^^^^^^^^^^^^^^^^^^^^
  |
note: ...which requires caching mir of `THING` for CTFE...
 --> src/lib.rs:7:1
  |
7 | pub static THING: Thing = Thing { next: &THING };
  | ^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires elaborating drops for `THING`...
 --> src/lib.rs:7:1
  |
7 | pub static THING: Thing = Thing { next: &THING };
  | ^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires borrow-checking `THING`...
 --> src/lib.rs:7:1
  |
7 | pub static THING: Thing = Thing { next: &THING };
  | ^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires promoting constants in MIR for `THING`...
 --> src/lib.rs:7:1
  |
7 | pub static THING: Thing = Thing { next: &THING };
  | ^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires const checking `THING`...
 --> src/lib.rs:7:1
  |
7 | pub static THING: Thing = Thing { next: &THING };
  | ^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires building MIR for `THING`...
 --> src/lib.rs:7:1
  |
7 | pub static THING: Thing = Thing { next: &THING };
  | ^^^^^^^^^^^^^^^^^^^^^^^
  = note: ...which again requires evaluating initializer of static `THING`, completing the cycle
  = note: cycle used when running analysis passes on this crate
  = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information

For more information about this error, try `rustc --explain E0391`.
error: could not compile `repro` (lib) due to 1 previous error

The error does not occur if you build without -Zdump-mir first.

$ cargo clean
$ cargo build
$ RUSTFLAGS=-Zdump-mir= cargo build

Meta

rustc 1.85.0-nightly (21fe748be 2024-12-11)
binary: rustc
commit-hash: 21fe748be15271ea5804e0507cd699b675efe038
commit-date: 2024-12-11
host: x86_64-unknown-linux-gnu
release: 1.85.0-nightly
LLVM version: 19.1.5

[compiler-errors]

cc @RalfJung, I think we probably shouldn't be printing the allocations of statics when dumping MIR (which requires computing the CTFE MIR so they can actually be evaluated), or at least we shouldn't be doing it until after optimized-mir is computed and not during the query itself.

[RalfJung]

Cc @oli-obk