"unstable fingerprints for predicates_of" with Clone trait

[AE1020]

This appears to be a transient error in an incremental build. I wrote up this issue and saved the stack when I got it. But when I did cargo clean and then cargo build it would not reproduce.

I had done rustup default nightly at some point, probably (?) without a cargo clean. There had been successful builds after that with nightly, but perhaps never a clean one. In case that had something to do with it, I tried:

$ rustup default stable
$ cargo clean
$ cargo build

# make change here

$ rustup default nightly
$ cargo build

But that didn't reproduce it either. :-(

---

The change was to manually implement a Clone trait that had previously been derived, in order to log or set breakpoints when a clone of a particular struct was made.

The patch I'm trying is to the Firecracker VMM, specifically to a struct in mmio.rs.

(Note: I don't have any Rust experience to speak of--and am merely trying to get some experience with it by poking around with Firecracker. But perhaps that makes me good at writing unexpected things that will crash Rustc.)

Code

#[derive(Debug, PartialEq, Versionize)]  // previously derived Clone
pub struct MMIODeviceInfo {
    pub addr: u64,
    pub len: u64,
    pub irqs: Vec<u32>,
}

impl Clone for MMIODeviceInfo {  // I added this "hooked" Clone
    fn clone(&self) -> Self {
        println!("!!! CLONING {}", self.addr);

        // Question: is this equivalent to what the derive(Clone) makes?
        MMIODeviceInfo {
            addr: self.addr.clone(),
            len: self.len.clone(),
            irqs: self.irqs.clone()
        }
    }
}

Meta

rustc 1.53.0-nightly (42816d61e 2021-04-24)
binary: rustc
commit-hash: 42816d61ead7e46d462df997958ccfd514f8c21c
commit-date: 2021-04-24
host: x86_64-unknown-linux-gnu
release: 1.53.0-nightly
LLVM version: 12.0.0

Error output

thread 'rustc' panicked at 'assertion failed: `(left == right)`
  left: `Some(Fingerprint(850694786735502876, 7070618143976680221))`,
 right: `Some(Fingerprint(4204111565215846862, 483459271662230500))`: found unstable fingerprints for predicates_of(core[ec89]::clone::Clone): GenericPredicates { parent: None, predicates: [(Binder(TraitPredicate(<Self as std::marker::Sized>), []), /home/ae1020/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/clone.rs:108:18: 108:23 (#0)), (Binder(TraitPredicate(<Self as std::clone::Clone>), []), /home/ae1020/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/clone.rs:108:1: 108:23 (#0))] }', /rustc/42816d61ead7e46d462df997958ccfd514f8c21c/compiler/rustc_query_system/src/query/plumbing.rs:593:5

Backtrace

   0: rust_begin_unwind
             at /rustc/42816d61ead7e46d462df997958ccfd514f8c21c/library/std/src/panicking.rs:493:5
   1: core::panicking::panic_fmt
             at /rustc/42816d61ead7e46d462df997958ccfd514f8c21c/library/core/src/panicking.rs:92:14
   2: core::panicking::assert_failed_inner
   3: core::panicking::assert_failed
   4: rustc_query_system::query::plumbing::incremental_verify_ich
   5: rustc_query_system::query::plumbing::load_from_disk_and_cache_in_memory
   6: rustc_query_system::query::plumbing::get_query_impl
   7: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::predicates_of
   8: rustc_trait_selection::traits::wf::WfPredicates::nominal_obligations
   9: rustc_trait_selection::traits::wf::WfPredicates::compute_trait_ref
  10: rustc_trait_selection::traits::wf::trait_obligations
  11: rustc_infer::infer::InferCtxtBuilder::enter
  12: rustc_typeck::check::wfcheck::check_item_well_formed
  13: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  14: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  15: rustc_query_system::query::plumbing::force_query_with_job
  16: rustc_query_system::query::plumbing::get_query_impl
  17: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::check_item_well_formed
  18: <rustc_typeck::check::wfcheck::CheckTypeWellFormedVisitor as rustc_hir::intravisit::Visitor>::visit_item
  19: rustc_data_structures::sync::par_for_each_in
  20: rustc_hir::hir::Crate::par_visit_all_item_likes
  21: rustc_session::session::Session::track_errors
  22: rustc_typeck::check_crate
  23: rustc_interface::passes::analysis
  24: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  25: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  26: rustc_data_structures::stack::ensure_sufficient_stack
  27: rustc_query_system::query::plumbing::force_query_with_job
  28: rustc_query_system::query::plumbing::get_query_impl
  29: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::analysis
  30: rustc_interface::passes::QueryContext::enter
  31: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  32: rustc_span::with_source_map
  33: rustc_interface::interface::create_compiler_and_run
  34: scoped_tls::ScopedKey<T>::set
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

[Aaron1011]

Duplicate of #84341

[Aaron1011]

This should be fixed in the latest nightly