ICE on type inference with for<'de> and Trait objects

[Michael-F-Bryan]

I've just encountered an interesting ICE on both stable and nightly which only presents itself when using for<'de> in a where clause and boxed trait objects.

A quick skim through the backtrace makes it look like an issue with type inference and the fact that the first argument is self.

Example:

extern crate serde;

use std::error::Error;
use std::iter;
use serde::Deserialize;


pub trait Paginated: Executor {
    fn paginated<T>(self) -> Box<Iterator<Item = Result<T, Box<Error>>>>
    where
        Self: Sized,
        T: for<'de> Deserialize<'de>,
    {
        match self.execute::<Vec<T>>() {
            Ok(got) => Box::new(iter::empty()),
            Err(e) => Box::new(iter::once(Err(e))),
        }
    }
}

trait Executor {
    fn execute<T>(self) -> Result<T, Box<Error>>
    where
        Self: Sized,
        T: for<'de> Deserialize<'de>,
    {
        unimplemented!()
    }
}

fn main() {}

(playground)

Backtrace:

$ RUST_BACKTRACE=full cargo run
...

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: rustc 1.22.1 (05e2e1c41 2017-11-22) running on x86_64-unknown-linux-gnu

note: run with `RUST_BACKTRACE=1` for a backtrace

thread 'rustc' panicked at 'assertion failed: !(self.has_self && idx == 0)', /checkout/src/librustc/ty/mod.rs:788:16
stack backtrace:
   0:     0x7fcfa867ce43 - std::sys::imp::backtrace::tracing::imp::unwind_backtrace::h8ed7485deb8ab958
                               at /checkout/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1:     0x7fcfa8677590 - std::sys_common::backtrace::_print::h3d4f9ea58578e60f
                               at /checkout/src/libstd/sys_common/backtrace.rs:69
   2:     0x7fcfa868a343 - std::panicking::default_hook::{{closure}}::h0088fe51b67c687c
                               at /checkout/src/libstd/sys_common/backtrace.rs:58
                               at /checkout/src/libstd/panicking.rs:381
   3:     0x7fcfa868a04a - std::panicking::default_hook::hf425c768c5ffbbad
                               at /checkout/src/libstd/panicking.rs:391
   4:     0x7fcfa868a807 - std::panicking::rust_panic_with_hook::h25b934bb4484e9e0
                               at /checkout/src/libstd/panicking.rs:577
   5:     0x7fcfa505aa3a - std::panicking::begin_panic::h00bf2a70e069c223
   6:     0x7fcfa536ab7f - rustc::ty::Generics::type_param::h91ef8c39b7e0fd49
   7:     0x7fcfa5223ae3 - rustc::infer::error_reporting::<impl rustc::infer::InferCtxt<'a, 'gcx, 'tcx>>::report_region_errors::h5eada194f4b8f339
   8:     0x7fcfa52491a7 - rustc::infer::InferCtxt::resolve_regions_and_report_errors::h64edcb890c069ae8
   9:     0x7fcfa764d2a5 - rustc_typeck::check::typeck_tables_of::{{closure}}::h042d0873aaf7fde0
  10:     0x7fcfa7649b3b - rustc_typeck::check::typeck_tables_of::he5b52d40ac01f6ff
  11:     0x7fcfa54198e4 - rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_tables_of<'tcx>>::force::h22c9013a5fcfb086
  12:     0x7fcfa541a341 - rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_tables_of<'tcx>>::try_get::hf118a95b7cc6e708
  13:     0x7fcfa550ae9a - rustc::ty::maps::TyCtxtAt::typeck_tables_of::h51c78abcf9c5a929
  14:     0x7fcfa5507653 - rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::typeck_tables_of::hbf69b4488e565710
  15:     0x7fcfa7648e27 - rustc_typeck::check::typeck_item_bodies::h39b104d6bb6d2f89
  16:     0x7fcfa5416b0d - rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_item_bodies<'tcx>>::force::h28d47d1ad55f84fa
  17:     0x7fcfa5417543 - rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_item_bodies<'tcx>>::try_get::h2e813186439f4ed0
  18:     0x7fcfa550ad74 - rustc::ty::maps::TyCtxtAt::typeck_item_bodies::h4b1084eafa435c5e
  19:     0x7fcfa5507623 - rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::typeck_item_bodies::hc5ad0d8db8d5fb90
  20:     0x7fcfa769dccb - rustc_typeck::check_crate::h855fcdb3ee4b5abc
  21:     0x7fcfa89aeb39 - rustc::ty::context::TyCtxt::create_and_enter::h3dad1968772b9cec
  22:     0x7fcfa8a2cd4b - rustc_driver::driver::compile_input::h4bf59ac61f928939
  23:     0x7fcfa8a489fe - rustc_driver::run_compiler::h2a410e29e6088b6b
  24:     0x7fcfa89677c7 - std::sys_common::backtrace::__rust_begin_short_backtrace::hb62d9d382e421fd7
  25:     0x7fcfa86c4bdc - __rust_maybe_catch_panic
                               at /checkout/src/libpanic_unwind/lib.rs:99
  26:     0x7fcfa89a0870 - <F as alloc::boxed::FnBox<A>>::call_box::h56ea5c52b2f008af
  27:     0x7fcfa868920b - std::sys::imp::thread::Thread::new::thread_start::hbaf1b5aa1ca8e3ea
                               at /checkout/src/liballoc/boxed.rs:736
                               at /checkout/src/libstd/sys_common/thread.rs:24
                               at /checkout/src/libstd/sys/unix/thread.rs:90
  28:     0x7fcfa3543089 - start_thread
  29:     0x7fcfa834b42e - __clone
  30:                0x0 - <unknown>

error: Could not compile `repo-backup`.

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

[mattsse]

I can also reproduce.
Think it's the same problem as in #46568
Apparently it was just fixed with #46722.

[pietroalbini]

The provided snippet doesn't ICE anymore on the beta channel. Closing this.