Rust 1.19 regression, scopeguard, ICE

[brson]

https://github.com/bluss/scopeguard

commit e1639812249432b5d4dc0fea3e804582a7092a50
Author: bluss <bluss@users.noreply.github.com>
Date:   Sat Jan 21 11:31:53 2017 +0100

    Add categories

brian@ip-10-145-43-250:/mnt2/dev⟫ rustc +nightly -Vv
rustc 1.19.0-nightly (0418fa9d3 2017-06-04)
binary: rustc
commit-hash: 0418fa9d382a47d782cc1e195c14573be9c32095
commit-date: 2017-06-04
host: x86_64-unknown-linux-gnu
release: 1.19.0-nightly
LLVM version: 4.0

101 brian@ip-10-145-43-250:~/dev/scopeguard⟫ RUST_BACKTRACE=1 cargo +nightly test
   Compiling scopeguard v0.3.2 (file:///mnt2/dev/scopeguard)
error: internal compiler error: unexpected panic

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 'already mutably borrowed: BorrowError', /checkout/src/libcore/result.rs:860
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
stack backtrace:
   0: std::sys::imp::backtrace::tracing::imp::unwind_backtrace
             at /checkout/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::_print
             at /checkout/src/libstd/sys_common/backtrace.rs:71
   2: std::panicking::default_hook::{{closure}}
             at /checkout/src/libstd/sys_common/backtrace.rs:60
             at /checkout/src/libstd/panicking.rs:355
   3: std::panicking::default_hook
             at /checkout/src/libstd/panicking.rs:365
   4: std::panicking::rust_panic_with_hook
             at /checkout/src/libstd/panicking.rs:549
   5: std::panicking::begin_panic
             at /checkout/src/libstd/panicking.rs:511
   6: std::panicking::begin_panic_fmt
             at /checkout/src/libstd/panicking.rs:495
   7: rust_begin_unwind
             at /checkout/src/libstd/panicking.rs:471
   8: core::panicking::panic_fmt
             at /checkout/src/libcore/panicking.rs:69
   9: core::result::unwrap_failed
  10: rustc::infer::InferCtxt::closure_type
  11: rustc::traits::select::SelectionContext::closure_trait_ref
  12: rustc::traits::select::SelectionContext::confirm_candidate
  13: rustc::traits::select::SelectionContext::select
  14: rustc::traits::project::assemble_candidates_from_impls::{{closure}}
  15: rustc::traits::project::assemble_candidates_from_impls
  16: rustc::traits::project::opt_normalize_projection_type
  17: rustc::traits::project::poly_project_and_unify_type::{{closure}}
  18: rustc::traits::project::poly_project_and_unify_type
  19: rustc::traits::select::SelectionContext::evaluate_predicate_recursively
  20: rustc::traits::select::SelectionContext::evaluate_predicates_recursively
  21: rustc::traits::select::SelectionContext::evaluate_candidate::{{closure}}
  22: rustc::infer::InferCtxt::probe
  23: rustc::traits::select::SelectionContext::evaluate_candidate
  24: rustc::traits::select::SelectionContext::evaluate_stack
  25: rustc::traits::select::SelectionContext::evaluate_predicate_recursively
  26: rustc::traits::select::SelectionContext::evaluate_obligation
  27: rustc_typeck::check::method::<impl rustc_typeck::check::FnCtxt<'a, 'gcx, 'tcx>>::lookup_method_in_trait
  28: rustc_typeck::check::FnCtxt::try_overloaded_lvalue_op
  29: rustc_typeck::check::FnCtxt::check_method_call
  30: rustc_typeck::check::FnCtxt::check_expr_kind
  31: rustc_typeck::check::FnCtxt::check_expr_with_expectation_and_lvalue_pref
  32: rustc_typeck::check::FnCtxt::check_method_call
  33: rustc_typeck::check::FnCtxt::check_expr_kind
  34: rustc_typeck::check::FnCtxt::check_expr_with_expectation_and_lvalue_pref
  35: rustc_typeck::check::FnCtxt::check_block_with_expected::{{closure}}
  36: rustc_typeck::check::FnCtxt::check_block_with_expected
  37: rustc_typeck::check::FnCtxt::check_expr_kind
  38: rustc_typeck::check::FnCtxt::check_expr_with_expectation_and_lvalue_pref
  39: rustc_typeck::check::FnCtxt::check_return_expr
  40: rustc_typeck::check::check_fn
  41: rustc_typeck::check::typeck_tables_of::{{closure}}
  42: rustc_typeck::check::typeck_tables_of
  43: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_tables_of<'tcx>>::try_get
  44: rustc::ty::maps::TyCtxtAt::typeck_tables_of
  45: rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::typeck_tables_of
  46: rustc_typeck::check::typeck_item_bodies
  47: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_item_bodies<'tcx>>::try_get
  48: rustc::ty::maps::TyCtxtAt::typeck_item_bodies
  49: rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::typeck_item_bodies
  50: rustc_typeck::check_crate
  51: rustc_driver::driver::phase_3_run_analysis_passes::{{closure}}
  52: rustc_driver::driver::phase_3_run_analysis_passes
  53: rustc_driver::driver::compile_input
  54: rustc_driver::run_compiler

error: Could not compile `scopeguard`.

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

cc @bluss

[Mark-Simulacrum]

4ed2eda -- #42281; cc @eddyb

[eddyb]

Reduced testcase (closure satisfying Fn bound on DerefMut impl used in autoderef):

use std::ops::{Deref, DerefMut};

struct CheckedDeref<T, F> {
    value: T,
    check: F
}

impl<F: Fn(&T) -> bool, T> Deref for CheckedDeref<T, F> {
    type Target = T;
    fn deref(&self) -> &T {
        assert!((self.check)(&self.value));
        &self.value
    }
}

impl<F: Fn(&T) -> bool, T> DerefMut for CheckedDeref<T, F> {
    fn deref_mut(&mut self) -> &mut T {
        assert!((self.check)(&self.value));
        &mut self.value
    }
}


fn main() {
    let mut v = CheckedDeref {
        value: vec![0],
        check: |v: &Vec<_>| !v.is_empty()
    };
    v.push(1);
    assert_eq!(*v, vec![0, 1]);
}

Working on a fix now.