Something to do with the parameter to AddAssign

[davidspies]

Note that adding the (redundant) constraint R2: AddAssign<R2> at line 16 makes the error go away.

Inlining the call to other.map at line 23 results in the compile-time message "cannot add-assign R2 to R2". Inlining the second call to map at line 23 makes the error go away.

Code

mod convenience_operators {
    use crate::{Op, Relation};
    use std::ops::AddAssign;
    use std::ops::Mul;

    impl<C: Op> Relation<C> {
        pub fn map<F: Fn(C::D) -> D2 + 'static, D2: 'static>(
            self,
            f: F,
        ) -> Relation<impl Op<D = D2, R = C::R>> {
            self.map_dr(move |x, r| (f(x), r))
        }
    }

    impl<K: 'static, V: 'static, C: Op<D = (K, V)>> Relation<C> {
        pub fn semijoin<C2: Op<D = K, R = R2>, R2, R3: AddAssign<R3>>(
            self,
            other: Relation<C2>,
        ) -> Relation<impl Op<D = C::D, R = R3>>
        where
            C::R: Mul<R2, Output = R3>,
        {
            self.join(other.map(|x| (x, ()))).map(|(k, x, ())| (k, x))
        }
    }
}

mod core {
    mod operator {
        mod join {
            use super::Op;
            use crate::core::Relation;
            use std::ops::{AddAssign, Mul};
            struct Join<LC, RC> {
                _left: LC,
                _right: RC,
            }
            impl<
                    LC: Op<D = (K, LD), R = LR>,
                    RC: Op<D = (K, RD), R = RR>,
                    K: 'static,
                    LD: 'static,
                    LR: AddAssign<LR> + Mul<RR, Output = OR>,
                    RD: 'static,
                    RR: AddAssign<RR>,
                    OR: AddAssign<OR>,
                > Op for Join<LC, RC>
            {
                type D = (K, LD, RD);
                type R = OR;
            }
            impl<K: 'static, D: 'static, C: Op<D = (K, D)>> Relation<C> {
                pub fn join<C2: Op<D = (K, D2)>, D2: 'static, OR: AddAssign<OR>>(
                    self,
                    other: Relation<C2>,
                ) -> Relation<impl Op<D = (K, D, D2), R = OR>>
                where
                    C::R: Mul<C2::R, Output = OR>,
                {
                    Relation {
                        inner: Join {
                            _left: self.inner,
                            _right: other.inner,
                        },
                    }
                }
            }
        }
        mod map {
            use super::Op;
            use crate::core::Relation;
            use std::ops::AddAssign;
            struct Map<C, MF> {
                _inner: C,
                _op: MF,
            }
            impl<
                    D1,
                    R1,
                    D2: 'static,
                    R2: AddAssign<R2>,
                    C: Op<D = D1, R = R1>,
                    MF: Fn(D1, R1) -> (D2, R2),
                > Op for Map<C, MF>
            {
                type D = D2;
                type R = R2;
            }
            impl<C: Op> Relation<C> {
                pub fn map_dr<F: Fn(C::D, C::R) -> (D2, R2), D2: 'static, R2: AddAssign<R2>>(
                    self,
                    f: F,
                ) -> Relation<impl Op<D = D2, R = R2>> {
                    Relation {
                        inner: Map {
                            _inner: self.inner,
                            _op: f,
                        },
                    }
                }
            }
        }
        use std::ops::AddAssign;
        pub trait Op {
            type D: 'static;
            type R: AddAssign<Self::R>;
        }
    }
    pub use self::operator::Op;
    #[derive(Clone)]
    pub struct Relation<C> {
        inner: C,
    }
}

use self::core::Op;
pub use self::core::Relation;

Meta

rustc --version --verbose:

rustc 1.52.0-nightly (07194ffcd 2021-02-10)
binary: rustc
commit-hash: 07194ffcd25b0871ce560b9f702e52db27ac9f77
commit-date: 2021-02-10
host: x86_64-unknown-linux-gnu
release: 1.52.0-nightly
LLVM version: 11.0.1

Error output

   Compiling dc2 v0.1.0 (/home/david/projects/dc2)
error: internal compiler error: compiler/rustc_traits/src/normalize_erasing_regions.rs:43:32: could not fully normalize `core::Relation<impl core::operator::Op>`

thread 'rustc' panicked at 'Box<Any>', /rustc/07194ffcd25b0871ce560b9f702e52db27ac9f77/library/std/src/panic.rs:59:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

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

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.52.0-nightly (07194ffcd 2021-02-10) running on x86_64-unknown-linux-gnu

note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental --crate-type lib

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
#0 [normalize_generic_arg_after_erasing_regions] normalizing `core::Relation<impl core::operator::Op>`
#1 [optimized_mir] optimizing MIR for `convenience_operators::<impl core::Relation<C>>::semijoin`
end of query stack
error: aborting due to previous error

error: could not compile `dc2`

To learn more, run the command again with --verbose.

Backtrace

stack backtrace:
   0: std::panicking::begin_panic
   1: std::panic::panic_any
   2: rustc_errors::HandlerInner::bug
   3: rustc_errors::Handler::bug
   4: rustc_middle::ty::context::tls::with_opt
   5: rustc_middle::util::bug::opt_span_bug_fmt
   6: rustc_middle::util::bug::bug_fmt
   7: rustc_infer::infer::InferCtxtBuilder::enter
   8: rustc_traits::normalize_erasing_regions::normalize_generic_arg_after_erasing_regions
   9: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  10: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  11: rustc_data_structures::stack::ensure_sufficient_stack
  12: rustc_query_system::query::plumbing::force_query_with_job
  13: rustc_query_system::query::plumbing::get_query_impl
  14: rustc_middle::ty::normalize_erasing_regions::<impl rustc_middle::ty::context::TyCtxt>::normalize_erasing_regions
  15: <rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt> as rustc_target::abi::LayoutOf>::layout_of
  16: <rustc_mir::transform::const_prop::ConstProp as rustc_mir::transform::MirPass>::run_pass
  17: rustc_mir::transform::run_passes
  18: rustc_mir::transform::optimized_mir
  19: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::optimized_mir>::compute
  20: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  21: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  22: rustc_data_structures::stack::ensure_sufficient_stack
  23: rustc_query_system::query::plumbing::force_query_with_job
  24: rustc_query_system::query::plumbing::get_query_impl
  25: rustc_metadata::rmeta::encoder::EncodeContext::encode_crate_root
  26: rustc_metadata::rmeta::encoder::encode_metadata_impl
  27: rustc_data_structures::sync::join
  28: rustc_metadata::rmeta::encoder::encode_metadata
  29: rustc_metadata::rmeta::decoder::cstore_impl::<impl rustc_middle::middle::cstore::CrateStore for rustc_metadata::creader::CStore>::encode_metadata
  30: rustc_middle::ty::context::TyCtxt::encode_metadata
  31: rustc_interface::passes::QueryContext::enter
  32: rustc_interface::queries::Queries::ongoing_codegen
  33: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  34: rustc_span::with_source_map
  35: rustc_interface::interface::create_compiler_and_run
  36: scoped_tls::ScopedKey<T>::set
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.