ICE: ... was matchable against ... but now is not

[nicholasbishop]

Here's the backtrace. Let me know if the code I was compiling would be helpful, I tagged the rev locally.

rustc 1.1.0-nightly (7bd71637c 2015-05-06) (built 2015-05-06)

$ RUST_BACKTRACE=1 cargo test   
Compiling dumbmath v0.1.6 (file:///home/nicholasbishop/dumbmath)
error: internal compiler error: Impl DefId { krate: 2, node: 26942 } was matchable against Obligation(predicate=Binder(TraitPredicate(<f32 as core::ops::Div<_>>)),depth=1) but now is not
note: the compiler unexpectedly panicked. this is a bug.
note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports
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:230

stack backtrace:
   1:     0x7fbee3ae6f89 - sys::backtrace::write::h89d94970ae1bc478fhs
   2:     0x7fbee3aeef09 - panicking::on_panic::h314cddb0409059cbkXw
   3:     0x7fbee3aaf0f2 - rt::unwind::begin_unwind_inner::hd6748515f1d9c0b2uCw
   4:     0x7fbee0e85fbd - rt::unwind::begin_unwind::h9184602946677297306
   5:     0x7fbee0e8667b - diagnostic::Handler::bug::h6d48c8060c15a3b4a2B
   6:     0x7fbee1c36304 - middle::traits::select::SelectionContext<'cx, 'tcx>::rematch_impl::h10b0cc0f4e83f0c3EuT
   7:     0x7fbee1c35c2f - middle::infer::InferCtxt<'a, 'tcx>::commit_if_ok::h17325861492725920879
   8:     0x7fbee1c1c8a5 - middle::traits::select::SelectionContext<'cx, 'tcx>::confirm_candidate::hca3234a85605343cUMS
   9:     0x7fbee1afacc5 - middle::traits::select::SelectionContext<'cx, 'tcx>::select::hec5ba022f7c648beiPQ
  10:     0x7fbee1c09d35 - middle::traits::project::project_type::h74992cfacc671364CwP
  11:     0x7fbee1c0896b - middle::traits::project::opt_normalize_projection_type::ha8866d0a50189fbcepP
  12:     0x7fbee1c0599f - middle::traits::project::project_and_unify_type::h1300a4d0fa05187d87O
  13:     0x7fbee1c03970 - middle::infer::InferCtxt<'a, 'tcx>::commit_if_ok::h107823834106425565
  14:     0x7fbee1bfb888 - middle::traits::fulfill::FulfillmentContext<'tcx>::select::hec0877a5f2e11ad0HHO
  15:     0x7fbee1bfb29b - middle::traits::fulfill::FulfillmentContext<'tcx>::select_where_possible::h301bc31d4e510c07VGO
  16:     0x7fbee323d048 - check::vtable::select_fcx_obligations_where_possible::h72b84a124c3a5b40I6b
  17:     0x7fbee325914a - check::FnCtxt<'a, 'tcx>::resolve_type_vars_if_possible::h74b2cbbcdf641686cPo
  18:     0x7fbee32b674e - check::op::check_binop::hba99f04615a48d79oYm
  19:     0x7fbee32ec9cd - check::check_expr_with_unifier::h12689752184703274217
  20:     0x7fbee3312c4b - check::check_decl_local::h28a2e7870f672b04j7r
  21:     0x7fbee32c23f1 - check::check_block_with_expected::h212bdec46f615ac8pds
  22:     0x7fbee32a7f36 - check::check_fn::h225bdd7ece966e55lSn
  23:     0x7fbee32bde27 - check::check_bare_fn::h8fed7360af87b5cbUHn
  24:     0x7fbee32c980c - check::check_method_body::h225a8a268d0d1168Ujo
  25:     0x7fbee32bbd85 - check::CheckItemBodiesVisitor<'a, 'tcx>.Visitor<'tcx>::visit_item::hb0162b7f82578cf4XEn
  26:     0x7fbee32bc1bf - check::CheckItemBodiesVisitor<'a, 'tcx>.Visitor<'tcx>::visit_item::hb0162b7f82578cf4XEn
  27:     0x7fbee3376c4a - check_crate::closure.38730
  28:     0x7fbee336ff80 - check_crate::hed85a8a5c9342eb05CC
  29:     0x7fbee4035c28 - driver::phase_3_run_analysis_passes::he0b331c645c77cdbtGa
  30:     0x7fbee401705c - driver::compile_input::h763ead6090436e8fQba
  31:     0x7fbee40cfeb1 - run_compiler::h711c4a29f8d270a365b
  32:     0x7fbee40cd702 - boxed::F.FnBox<A>::call_box::h12199818508070417299
  33:     0x7fbee40cccc9 - rt::unwind::try::try_fn::h5660428370877252098
  34:     0x7fbee3b62898 - rust_try_inner
  35:     0x7fbee3b62885 - rust_try
  36:     0x7fbee40ccf64 - boxed::F.FnBox<A>::call_box::h5514408293737026672
  37:     0x7fbee3aedca1 - sys::thread::Thread::new::thread_start::hfd3ca3d51ffcfe41QIv
  38:     0x7fbeddb82529 - start_thread
  39:     0x7fbee374022c - __clone
  40:                0x0 - <unknown>

Build failed, waiting for other jobs to finish...
error: internal compiler error: Impl DefId { krate: 2, node: 26942 } was matchable against Obligation(predicate=Binder(TraitPredicate(<f32 as core::ops::Div<_>>)),depth=1) but now is not
note: the compiler unexpectedly panicked. this is a bug.
note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports
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:230

stack backtrace:
   1:     0x7f920f378f89 - sys::backtrace::write::h89d94970ae1bc478fhs
   2:     0x7f920f380f09 - panicking::on_panic::h314cddb0409059cbkXw
   3:     0x7f920f3410f2 - rt::unwind::begin_unwind_inner::hd6748515f1d9c0b2uCw
   4:     0x7f920c717fbd - rt::unwind::begin_unwind::h9184602946677297306
   5:     0x7f920c71867b - diagnostic::Handler::bug::h6d48c8060c15a3b4a2B
   6:     0x7f920d4c8304 - middle::traits::select::SelectionContext<'cx, 'tcx>::rematch_impl::h10b0cc0f4e83f0c3EuT
   7:     0x7f920d4c7c2f - middle::infer::InferCtxt<'a, 'tcx>::commit_if_ok::h17325861492725920879
   8:     0x7f920d4ae8a5 - middle::traits::select::SelectionContext<'cx, 'tcx>::confirm_candidate::hca3234a85605343cUMS
   9:     0x7f920d38ccc5 - middle::traits::select::SelectionContext<'cx, 'tcx>::select::hec5ba022f7c648beiPQ
  10:     0x7f920d49bd35 - middle::traits::project::project_type::h74992cfacc671364CwP
  11:     0x7f920d49a96b - middle::traits::project::opt_normalize_projection_type::ha8866d0a50189fbcepP
  12:     0x7f920d49799f - middle::traits::project::project_and_unify_type::h1300a4d0fa05187d87O
  13:     0x7f920d495970 - middle::infer::InferCtxt<'a, 'tcx>::commit_if_ok::h107823834106425565
  14:     0x7f920d48d888 - middle::traits::fulfill::FulfillmentContext<'tcx>::select::hec0877a5f2e11ad0HHO
  15:     0x7f920d48d29b - middle::traits::fulfill::FulfillmentContext<'tcx>::select_where_possible::h301bc31d4e510c07VGO
  16:     0x7f920eacf048 - check::vtable::select_fcx_obligations_where_possible::h72b84a124c3a5b40I6b
  17:     0x7f920eaeb14a - check::FnCtxt<'a, 'tcx>::resolve_type_vars_if_possible::h74b2cbbcdf641686cPo
  18:     0x7f920eb4874e - check::op::check_binop::hba99f04615a48d79oYm
  19:     0x7f920eb7e9cd - check::check_expr_with_unifier::h12689752184703274217
  20:     0x7f920eba4c4b - check::check_decl_local::h28a2e7870f672b04j7r
  21:     0x7f920eb543f1 - check::check_block_with_expected::h212bdec46f615ac8pds
  22:     0x7f920eb39f36 - check::check_fn::h225bdd7ece966e55lSn
  23:     0x7f920eb4fe27 - check::check_bare_fn::h8fed7360af87b5cbUHn
  24:     0x7f920eb5b80c - check::check_method_body::h225a8a268d0d1168Ujo
  25:     0x7f920eb4dd85 - check::CheckItemBodiesVisitor<'a, 'tcx>.Visitor<'tcx>::visit_item::hb0162b7f82578cf4XEn
  26:     0x7f920eb4e1bf - check::CheckItemBodiesVisitor<'a, 'tcx>.Visitor<'tcx>::visit_item::hb0162b7f82578cf4XEn
  27:     0x7f920ec08c4a - check_crate::closure.38730
  28:     0x7f920ec01f80 - check_crate::hed85a8a5c9342eb05CC
  29:     0x7f920f8c7c28 - driver::phase_3_run_analysis_passes::he0b331c645c77cdbtGa
  30:     0x7f920f8a905c - driver::compile_input::h763ead6090436e8fQba
  31:     0x7f920f961eb1 - run_compiler::h711c4a29f8d270a365b
  32:     0x7f920f95f702 - boxed::F.FnBox<A>::call_box::h12199818508070417299
  33:     0x7f920f95ecc9 - rt::unwind::try::try_fn::h5660428370877252098
  34:     0x7f920f3f4898 - rust_try_inner
  35:     0x7f920f3f4885 - rust_try
  36:     0x7f920f95ef64 - boxed::F.FnBox<A>::call_box::h5514408293737026672
  37:     0x7f920f37fca1 - sys::thread::Thread::new::thread_start::hfd3ca3d51ffcfe41QIv
  38:     0x7f9209414529 - start_thread
  39:     0x7f920efd222c - __clone
  40:                0x0 - <unknown>

Could not compile `dumbmath`.

[bluss]

Maybe a duplicate of #22645

Code is always useful, the best is a reduced testcase that still exhibits the problem.

[nicholasbishop]

Here's the tag for that code: https://github.com/nicholasbishop/dumbmath-rs/tree/ice-25235

I haven't tried to reduce it to a better testcase since it looks like it's probably the same as the bug you linked to (which has a nice small test case in this comment: #22645 (comment))

[arielb1]

Seems like a duplicate of #24352 (and its duplicates #23825, #22645).