!Struct bounds break

[OptimisticPeach]

I made a typo. I tried to type this:

struct Foo;
trait B {}
impl B for Foo {}
struct C<T: !B>(std::marker::PhantomData<T>);

Yet instead I got:

struct Foo;
trait B {}
impl B for Foo {}
struct C<T: !Foo>(std::marker::PhantomData<T>);

Which can be summarized to

struct Foo;
struct C<T: !Foo>;

I expected it to tell me that it wouldn't be able to use a struct as a type parameter constraint like with this case:

error[E0404]: expected trait, found struct `Foo`
 --> src\main.rs:2:13
  |
2 | struct C<T: Foo>;
  |             ^^^ not a trait

Meta

> cargo build
Compiling forum_examples v0.1.0 (C:\Users\User\Desktop\forum_examples)
thread 'rustc' panicked at 'called `Option::unwrap()` on a `None` value', src\libcore\option.rs:345:21
stack backtrace:
   0: std::sys_common::alloc::realloc_fallback
   1: std::panicking::take_hook
   2: std::panicking::take_hook
   3: std::panicking::rust_panic_with_hook
   4: std::panicking::begin_panic_fmt
   5: rust_begin_unwind
   6: core::panicking::panic_fmt
   7: core::panicking::panic
   8: syntax::parse::parser::Parser::parse_block
   9: syntax::parse::parser::Parser::parse_block
  10: syntax::parse::parser::Parser::parse_block
  11: syntax::parse::parser::Parser::default_submod_path
  12: syntax::parse::parser::Parser::default_submod_path
  13: syntax::parse::parser::Parser::parse_item
  14: syntax::parse::parser::Parser::parse_visibility
  15: syntax::parse::parser::Parser::parse_crate_mod
  16: syntax::parse::parse_crate_from_file
  17: rustc_driver::profile::dump
  18: rand::os::OsRng::new
  19: rustc_driver::driver::phase_1_parse_input
  20: rustc_driver::driver::compile_input
  21: rustc_driver::run_compiler
  22: <rustc_driver::CompilationFailure as core::fmt::Debug>::fmt
  23: rustc_driver::run_compiler
  24: <rustc_driver::CompilationFailure as core::fmt::Debug>::fmt
  25: _rust_maybe_catch_panic
  26: <rustc_driver::profile::trace::Query as core::fmt::Debug>::fmt
  27: std::sys::windows::thread::Thread::new
  28: BaseThreadInitThunk
  29: RtlUserThreadStart

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 1.34.0-nightly (097c04cf4 2019-02-24) running on x86_64-pc-windows-msvc

note: compiler flags: -C debuginfo=2 -C incremental --crate-type bin

note: some of the compiler flags provided by cargo are hidden

[jonas-schievink]

Duplicate of #58857