Bug with new operators traits

[rvlander]

➜  matrix-rs git:(master) ✗ RUST_BACKTRACE=1 cargo build --verbose
       Fresh rustc-serialize v0.2.4
       Fresh num v0.1.5
   Compiling matrix-rs v0.0.1 (file:///home/rvlander/CloudStation/WIP/matrix-rs)
     Running `rustc /home/rvlander/CloudStation/WIP/matrix-rs/src/lib.rs --crate-name matrix-rs --crate-type lib -g -C metadata=911cbf09ca74d9fa -C extra-filename=-911cbf09ca74d9fa --out-dir /home/rvlander/CloudStation/WIP/matrix-rs/target --emit=dep-info,link -L /home/rvlander/CloudStation/WIP/matrix-rs/target -L /home/rvlander/CloudStation/WIP/matrix-rs/target/deps --extern num=/home/rvlander/CloudStation/WIP/matrix-rs/target/deps/libnum-99d6507e3aad728a.rlib`
/home/rvlander/CloudStation/WIP/matrix-rs/src/matrix/dense_matrix.rs:54:1: 58:2 error: internal compiler error: impl `VtableImpl(impl_def_id=DefId { krate: 0, node: 1042 }:matrix::dense_matrix::DenseMatrix<T>.Add, substs=Substs[types=[[_];[];[]], regions=[[];[];[]]], nested=[[Obligation(predicate=Binder(TraitPredicate(TraitRef(T, core::kinds::Sized))),depth=1), Obligation(predicate=Binder(TraitPredicate(TraitRef(T, core::kinds::Copy))),depth=1), Obligation(predicate=Binder(TraitPredicate(TraitRef(T, core::ops::Add))),depth=1)];[];[]])` did not contain projection for `Obligation(predicate=<matrix::dense_matrix::DenseMatrix<T> as TraitRef(matrix::dense_matrix::DenseMatrix<T>, core::ops::Add)>::Output,depth=0)`
/home/rvlander/CloudStation/WIP/matrix-rs/src/matrix/dense_matrix.rs:54 impl <T: Add<T> + Copy> Add for DenseMatrix<T> {
/home/rvlander/CloudStation/WIP/matrix-rs/src/matrix/dense_matrix.rs:55     fn add(self, rhs: DenseMatrix<T>) -> DenseMatrix<T> {
/home/rvlander/CloudStation/WIP/matrix-rs/src/matrix/dense_matrix.rs:56         self.__add(rhs)
/home/rvlander/CloudStation/WIP/matrix-rs/src/matrix/dense_matrix.rs:57     }
/home/rvlander/CloudStation/WIP/matrix-rs/src/matrix/dense_matrix.rs:58 }
note: the compiler unexpectedly panicked. this is a bug.
note: we would appreciate a bug report: http://doc.rust-lang.org/complement-bugreport.html
note: run with `RUST_BACKTRACE=1` for a backtrace
thread 'rustc' panicked at 'Box<Any>', /home/rustbuild/src/rust-buildbot/slave/nightly-dist-rustc-linux/build/src/libsyntax/diagnostic.rs:123

stack backtrace:
   1:     0x7f7c86e9b920 - sys::backtrace::write::h36422e877a8b3158yQs
   2:     0x7f7c86ec1650 - failure::on_fail::hde5005d61795902da3y
   3:     0x7f7c86e274a0 - rt::unwind::begin_unwind_inner::ha0668a3a9d73b9a7RHy
   4:     0x7f7c81d00af0 - rt::unwind::begin_unwind::h9147230717703493418
   5:     0x7f7c81d00a80 - diagnostic::SpanHandler::span_bug::hee7de6e88971705bDFF
   6:     0x7f7c851fbc70 - middle::traits::project::project_type::ha3169b6d00cba236CYP
   7:     0x7f7c851f8dd0 - middle::traits::project::opt_normalize_projection_type::h52e80e1c888609adFQP
   8:     0x7f7c851e6890 - middle::traits::project::normalize_projection_type::had1d9d27edaeb68fgPP
   9:     0x7f7c851fa270 - middle::traits::project::AssociatedTypeNormalizer<'a, 'b, 'tcx>.TypeFolder<'tcx>::fold_ty::h8977cf1010cf2ef8RNP
  10:     0x7f7c864b7990 - middle::ty_fold::TypeFolder::fold_trait_ref::h15244371943192340039
  11:     0x7f7c864b85c0 - middle::ty_fold::VecPerParamSpace<T>.TypeFoldable<'tcx>::fold_with::h3029018912722243389
  12:     0x7f7c864d3b40 - check::FnCtxt<'a, 'tcx>::instantiate_bounds::haf69ce16fdf22227Nul
  13:     0x7f7c864ec870 - check::wf::CheckTypeWellFormedVisitor<'ccx, 'tcx>::check_impl::closure.30018
  14:     0x7f7c864e8ce0 - check::wf::CheckTypeWellFormedVisitor<'ccx, 'tcx>::with_fcx::h0df2a1129da2a633Hfi
  15:     0x7f7c864ef760 - check::wf::CheckTypeWellFormedVisitor<'ccx, 'tcx>.Visitor<'v>::visit_item::hc72c9294b1b3f21ftoi
  16:     0x7f7c864f15c0 - visit::walk_mod::h2450081392115226323
  17:     0x7f7c864ef760 - check::wf::CheckTypeWellFormedVisitor<'ccx, 'tcx>.Visitor<'v>::visit_item::hc72c9294b1b3f21ftoi
  18:     0x7f7c864f15c0 - visit::walk_mod::h2450081392115226323
  19:     0x7f7c864ef760 - check::wf::CheckTypeWellFormedVisitor<'ccx, 'tcx>.Visitor<'v>::visit_item::hc72c9294b1b3f21ftoi
  20:     0x7f7c866ddbd0 - check_crate::unboxed_closure.40283
  21:     0x7f7c866d8820 - check_crate::h4ba306a17295b431iux
  22:     0x7f7c873dc600 - driver::phase_3_run_analysis_passes::h56810662503f92d8Sva
  23:     0x7f7c873caaa0 - driver::compile_input::h8d0abf631800220evba
  24:     0x7f7c87496070 - thunk::F.Invoke<A, R>::invoke::h13263903969514368718
  25:     0x7f7c87494e20 - rt::unwind::try::try_fn::h2272437873322108176
  26:     0x7f7c86f258b0 - rust_try_inner
  27:     0x7f7c86f258a0 - rust_try
  28:     0x7f7c87495170 - thunk::F.Invoke<A, R>::invoke::h17236552692728063371
  29:     0x7f7c86ead490 - sys::thread::thread_start::hd19c7749b7af23e8EGv
  30:     0x7f7c81525250 - start_thread
  31:     0x7f7c86ae2219 - clone
  32:                0x0 - <unknown>

Could not compile `matrix-rs`.

Caused by:
  Process didn't exit successfully: `rustc /home/rvlander/CloudStation/WIP/matrix-rs/src/lib.rs --crate-name matrix-rs --crate-type lib -g -C metadata=911cbf09ca74d9fa -C extra-filename=-911cbf09ca74d9fa --out-dir /home/rvlander/CloudStation/WIP/matrix-rs/target --emit=dep-info,link -L /home/rvlander/CloudStation/WIP/matrix-rs/target -L /home/rvlander/CloudStation/WIP/matrix-rs/target/deps --extern num=/home/rvlander/CloudStation/WIP/matrix-rs/target/deps/libnum-99d6507e3aad728a.rlib` (status=101)

[japaric]

Probably a duplicate of #20553 / #20347

From the error message, it looks like you need to add the associated Output type to your Add impl.

impl <T: Add<T> + Copy> Add for DenseMatrix<T> {
    type Output = DenseMatrix<T>;  // <-- Add this

    fn add(self, rhs: DenseMatrix<T>) -> DenseMatrix<T> {
        self.__add(rhs)
    }
}

[rvlander]

Why do we need to define such a type now ? It does not seem usefull from a user point of view. Is it to help the compiler in some sort? Plus: what is this syntax ? <Self as Add<RHS>>::Output (cf reference API)

[huonw]

Why do we need to define such a type now ? ... Is it to help the compiler in some sort?

It is to help you. It defines what the result of the operation is, e.g. one might implement Mul<Vector<T>> for DenseMatrix<T> with Output = Vector<T>, and Mul<DenseMatrix<T>> for DenseMatrix<T> with Output = DenseMatrix<T> to allow multiplying two matrices and a matrix and a vector.

Plus: what is this syntax ? <Self as Add<RHS>>::Output (cf reference API)

It is how one writes the path to one of these associated types. https://github.com/rust-lang/rfcs/blob/master/text/0195-associated-items.md contains (a lot) more details.

Closing as a dupe of #20347; thanks for filing!

[rvlander]

Thx.