Rust ICE when using for all binder (panics in MIR) on stable 1.34.0 and nightly 1.35.0

[RustyYato]

pub trait Generator<'this> {
    type Yield: 'this;
    
    fn next(&'this mut self) -> Option<Self::Yield>;
}

pub trait FromGenerator<'gen, G: Generator<'gen>> {
    fn from_generator(g: G) -> Self;
}

impl<T, G> FromGenerator<'_, G> for Vec<T>
where G: for<'a> Generator<'a, Yield = T> {
    fn from_generator(mut g: G) -> Self {
        let mut vec = Self::new();

        while let Some(x) = g.next() {
            vec.push(x)
        }

        vec
    }
}

pub struct Iter<I: ?Sized>(I);

impl<'this, I: ?Sized + Iterator> Generator<'this> for Iter<I> where I::Item: 'this {
    type Yield = I::Item;

    fn next(&'this mut self) -> Option<Self::Yield> {
        self.0.next()
    }
}

fn main() {
    let indicies = [];
    Vec::<&u32>::from_generator(Iter(indicies.iter()));
}

While I was trying to make a general Generator impl, I came across this ICE. Note that inlining indicies makes this ICE go away.

[jonas-schievink]

thread 'rustc' panicked at 'called `Option::unwrap()` on a `None` value', src/libcore/option.rs:347:21
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:39
   1: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:71
   2: std::panicking::default_hook::{{closure}}
             at src/libstd/sys_common/backtrace.rs:59
             at src/libstd/panicking.rs:197
   3: std::panicking::default_hook
             at src/libstd/panicking.rs:211
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:478
   6: std::panicking::continue_panic_fmt
             at src/libstd/panicking.rs:381
   7: rust_begin_unwind
             at src/libstd/panicking.rs:308
   8: core::panicking::panic_fmt
             at src/libcore/panicking.rs:85
   9: core::panicking::panic
             at src/libcore/panicking.rs:49
  10: rustc_mir::borrow_check::nll::region_infer::error_reporting::<impl rustc_mir::borrow_check::nll::region_infer::RegionInferenceContext>::free_region_constraint_info
  11: rustc_mir::borrow_check::nll::explain_borrow::<impl rustc_mir::borrow_check::MirBorrowckCtxt>::explain_why_borrow_contains_point
  12: rustc_mir::borrow_check::error_reporting::<impl rustc_mir::borrow_check::MirBorrowckCtxt>::report_borrowed_value_does_not_live_long_enough
  13: rustc_mir::borrow_check::MirBorrowckCtxt::check_for_invalidation_at_exit
  14: rustc_mir::borrow_check::flows::Flows::with_outgoing_borrows
  15: <rustc_mir::borrow_check::MirBorrowckCtxt as rustc_mir::dataflow::DataflowResultsConsumer>::visit_terminator_entry
  16: rustc_mir::borrow_check::do_mir_borrowck
  17: rustc::ty::context::GlobalCtxt::enter_local
  18: rustc_mir::borrow_check::mir_borrowck
  19: rustc::ty::query::__query_compute::mir_borrowck
  20: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::mir_borrowck>::compute
  21: rustc::dep_graph::graph::DepGraph::with_task_impl
  22: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  23: rustc::ty::<impl rustc::ty::context::TyCtxt>::par_body_owners
  24: rustc::util::common::time
  25: rustc_interface::passes::analysis
  26: rustc::ty::query::__query_compute::analysis
  27: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::analysis>::compute
  28: rustc::dep_graph::graph::DepGraph::with_task_impl
  29: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  30: rustc_interface::passes::BoxedGlobalCtxt::access::{{closure}}
  31: rustc_interface::passes::create_global_ctxt::{{closure}}
  32: rustc_interface::passes::BoxedGlobalCtxt::enter
  33: rustc_interface::interface::run_compiler_in_existing_thread_pool
  34: std::thread::local::LocalKey<T>::with
  35: scoped_tls::ScopedKey<T>::set
  36: syntax::with_globals
query stack during panic:
#0 [mir_borrowck] processing `main`
#1 [analysis] running analysis passes on this crate
end of query stack

[RustyYato]

@jonas-schievink thanks for putting the stack-trace, I forgot about that

This also works

Vec::<u32>::from_generator(Iter(indicies.iter().cloned()));

[matthewjasper]

Small repro:

pub trait Outlives<'this> {}

impl<'this, T> Outlives<'this> for T where T: 'this {}

fn assert_static_via_hrtb<G>(_: G) where for<'a> G: Outlives<'a> {}

fn main() {
    let local = 0;
    assert_static_via_hrtb(&local);
}

I'll try to have a PR up for this next week.

[jonas-schievink]

Another repro from #60314:

trait Trait {
    type AssociatedType;
}

impl<'a, T : 'a> Trait for &'a T {
    type AssociatedType = &'a ();
}

/// Calling this with some T when we don't have `T : 'static` leads to an ICE
fn foo<T> (_: &'_ T)
where
    for<'a> &'a T : Trait<AssociatedType = &'a ()>,
{}

/// proof
fn main ()
{
    use ::core::convert::identity as force_local;
    match force_local(()) { ref not_static => {
        foo(&not_static);
    }}
}