ICE: In function receiving a boxed Invoke: 'rustc' panicked at 'assertion failed: !ty::type_needs_infer(ty)'

[Munksgaard]

The following code results in an internal compiler error:

#![feature(default_type_params)]

use std::thunk::Invoke;

fn foo(x: Box<for <'a>Invoke<&'a int, ()>>) {
}

fn bar() {
    foo( box () (move |: _| () ))
}

fn main() {
}

Compiler output:

$ RUST_BACKTRACE=1 rustc foo.rs
error: internal compiler error: unexpected panic
note: the compiler unexpectedly panicked. this is a bug.
note: we would appreciate a bug report: http://doc.rust-lang.org/complement-bugreport.html
note: run with `RUST_BACKTRACE=1` for a backtrace
task 'rustc' panicked at 'assertion failed: !ty::type_needs_infer(ty)', /home/munksgaard/src/rust/src/librustc_typeck/
lib.rs:131                                                                                                           

stack backtrace:
   1:     0x7f87b8a7dcf0 - rt::backtrace::imp::write::h645bafd98e8e710ffVx
   2:     0x7f87b8a810c0 - failure::on_fail::hadfa9c4bd89befdeImy
   3:     0x7f87b86c05d0 - unwind::begin_unwind_inner::hb7b66784235a0c45zNc
   4:     0x7f87b7c4e200 - unwind::begin_unwind::h6432056029046382294
   5:     0x7f87b7c77a50 - write_ty_to_tcx::h531c5306c5a4ce51HFy
   6:     0x7f87b7c6f870 - check::writeback::WritebackCx<'cx, 'tcx>::visit_node_id::he6b1ea82aefc9e13rZb
   7:     0x7f87b7c69180 - check::writeback::WritebackCx<'cx, 'tcx>.Visitor<'v>::visit_expr::h2e5bb818aa1baec7SOb
   8:     0x7f87b7c69180 - check::writeback::WritebackCx<'cx, 'tcx>.Visitor<'v>::visit_expr::h2e5bb818aa1baec7SOb
   9:     0x7f87b7d3cd40 - check::check_bare_fn::h47fbea7c0e66b231Pbk
  10:     0x7f87b7d348d0 - check::check_item::haae896fdd12b9182fvk
  11:     0x7f87b7f8c6d0 - check_crate::unboxed_closure.42749
  12:     0x7f87b7f873e0 - check_crate::h7f1d4273943762142Wy
  13:     0x7f87b8ed0530 - driver::phase_3_run_analysis_passes::h9674b56be39567edEta
  14:     0x7f87b8eb3950 - driver::compile_input::ha2f50471fb032db2rba
  15:     0x7f87b90677f0 - run_compiler::h6ae6cbe07908d3f9AYb
  16:     0x7f87b905e430 - thunk::F.Invoke<A, R>::invoke::h13189201362017435713
  17:     0x7f87b8a560a0 - thunk::F.Invoke<A, R>::invoke::h392198810864924209
  18:     0x7f87b86bed40 - task::Task::spawn_thunk::closure.5776
  19:     0x7f87b871dd20 - rust_try_inner
  20:     0x7f87b871dd10 - rust_try
  21:     0x7f87b86bee50 - unwind::try::h9da252fcf57eda5bQCc
  22:     0x7f87b86bebe0 - task::Task::run::ha8da221d1b1071efRNb
  23:     0x7f87b86be350 - thunk::F.Invoke<A, R>::invoke::h1465999670317872655
  24:     0x7f87b86bfca0 - thread::thread_start::hbb38abc3a96b7cc5b5b
  25:     0x7f87b34c7160 - start_thread
  26:     0x7f87b839dc69 - __clone
  27:                0x0 - <unknown>

$ rustc --version
rustc 0.13.0-dev (126db549b 2014-12-15 00:07:35 +0000)

[Munksgaard]

To clarify, this works fine with rust 0.12:

fn foo(x: proc(&int)) {
}

fn bar() {
    foo(proc(_)())
}

fn main() {
}

$ rustc-0.12.0 --version
rustc 0.12.0-dev

[Munksgaard]

These errors stopped appearing sometime in the last couple of weeks. The code above compiles when the boxed closure is explicitly typed as such:

#![feature(default_type_params)]

use std::thunk::Invoke;

fn foo(x: Box<for <'a>Invoke<&'a int, ()>>) {
}

fn bar() {
    foo( box () (move |: _: &int| () ))
}

fn main() {
}

However, without the explicit type declaration, it produces some rather weird type errors. I've created a new issue (#20528) to fix this, and am now closing this as resolved.