Trouble passing closures with borrowed pointers inside options

[SiegeLord]

rustc 0.9-pre (aa4455e 2013-12-06 01:11:18 -0800)

Consider this code and errors:

fn main()
{
    fn test1(x: Option<|y: &int|>) {}

    test1(Some(|y| {}));
    test1(Some(|y: &int| {}));

    fn test2(x: Option<|y: Option<|z: &int|>|>) {}

    test2(Some(|y| {}));
    test2(Some(|y: Option<|z: &int|>| {}));
}

test.rs:7:7: 7:20 error: mismatched types: expected `std::option::Option<|&int|>` but found `std::option::Option<|<V1>|>` (expected concrete lifetime, but found bound lifetime parameter &)
test.rs:7       test1(Some(|y| {}));
                      ^~~~~~~~~~~~~
note: expected concrete lifetime is lifetime ReInfer(ReSkolemized(0u, BrAnon(0u)))
test.rs:10:7: 10:20 error: mismatched types: expected `std::option::Option<|std::option::Option<|&int|>|>` but found `std::option::Option<|<V8>|>` (expected concrete lifetime, but found bound lifetime parameter &)
test.rs:10      test2(Some(|y| {}));
                      ^~~~~~~~~~~~~
note: expected concrete lifetime is lifetime ReInfer(ReSkolemized(5u, BrAnon(0u)))
task 'rustc' failed at 'assertion failed: !r0.is_bound()', /home/siege/src/rust2/src/librustc/middle/typeck/infer/lub.rs:157
error: internal compiler error: unexpected failure
This message reflects a bug in the Rust compiler. 
We would appreciate a bug report: https://github.com/mozilla/rust/wiki/HOWTO-submit-a-Rust-bug-report
note: the compiler hit an unexpected failure path. this is a bug
note: try running with RUST_LOG=rustc=1 to get further details and report the results to github.com/mozilla/rust/issues
task '<main>' failed at 'explicit failure', /home/siege/src/rust2/src/librustc/lib.rs:390

As you can see, in case of test1, it has trouble inferring the type of the closure parameter, but if you specify it manually it works. In the case of test2 specifying it manually crashes the compiler outright. Note that both cases work just fine if you remove all the Options.

[erickt]

visiting for triage. It can be simplified to:

fn main()
{
    fn test2(_x: Option<|y: Option<|z: &int|>|>) {}

    test2(Some(|y: Option<|z: &int|>| {}));
}

It's erroring with:

error: internal compiler error: unexpected failure
note: the compiler hit an unexpected failure path. this is a bug.
note: we would appreciate a bug report: http://static.rust-lang.org/doc/master/complement-bugreport.html
note: run with `RUST_BACKTRACE=1` for a backtrace
task 'rustc' failed at 'assertion failed: !r0.is_bound()', /Users/erickt/rust/rust-master/src/librustc/middle/typeck/infer/lub.rs:154
stack backtrace:
   1:        0x112b345b5 - rt::backtrace::imp::write::hae9e0c8649bd0651E1F::v0.11.pre
   2:        0x112aa16ae - rt::unwind::begin_unwind_inner::hd5684ca19e9518eaIBF::v0.11.pre
   3:        0x112aa01d7 - rt::unwind::begin_unwind_fmt::hac2a7e1b9194970bSAF::v0.11.pre
   4:        0x1100948dc - middle::typeck::infer::lub::Lub<'f>.Combine::fn_sigs::closure.70100
   5:        0x10ff35076 - middle::ty_fold::RegionFolder<'a>.TypeFolder::fold_region::h7dda58a08c21a343l0Q::v0.11.pre
   6:        0x10ff347c5 - middle::ty_fold::super_fold_sty::h13291029136304019429::v0.11.pre
   7:        0x10fefb2a0 - middle::ty_fold::RegionFolder<'a>.TypeFolder::fold_ty::h6392d01fc77bc3084XQ::v0.11.pre
   8:        0x10ff237e0 - iter::Iterator::collect::h15992120228646370080::v0.11.pre
   9:        0x10ff35160 - middle::ty_fold::super_fold_sig::h13577425788296859040::v0.11.pre
  10:        0x10ff34cad - middle::ty_fold::super_fold_sty::h13291029136304019429::v0.11.pre
  11:        0x10fefb2a0 - middle::ty_fold::RegionFolder<'a>.TypeFolder::fold_ty::h6392d01fc77bc3084XQ::v0.11.pre
  12:        0x10ff237e0 - iter::Iterator::collect::h15992120228646370080::v0.11.pre
  13:        0x10ff34ea3 - middle::ty_fold::TypeFolder::fold_substs::h17351997724182444375::v0.11.pre
  14:        0x10ff34604 - middle::ty_fold::super_fold_sty::h13291029136304019429::v0.11.pre
  15:        0x10fefb2a0 - middle::ty_fold::RegionFolder<'a>.TypeFolder::fold_ty::h6392d01fc77bc3084XQ::v0.11.pre
  16:        0x10ff237e0 - iter::Iterator::collect::h15992120228646370080::v0.11.pre
  17:        0x110093e20 - middle::typeck::infer::lub::Lub<'f>.Combine::fn_sigs::h2881151a6d6777f5NMi::v0.11.pre
  18:        0x11009c9d8 - middle::typeck::infer::combine::Combine::closure_tys::h14040719990868578090::v0.11.pre
  19:        0x110096d9b - middle::typeck::infer::lattice::super_lattice_tys::h7287454358332737396::v0.11.pre
  20:        0x110084823 - middle::typeck::infer::lattice::ty..t.LatticeValue::lub::hcf901c13c4c1fce75Bh::v0.11.pre
  21:        0x1100848cc - middle::typeck::infer::lattice::LatticeValue::lub::as_closure.69820
  22:        0x110084437 - middle::typeck::infer::lattice::CombineFields<'f>.CombineFieldsLatticeMethods::merge_bnd::h13068228610379944350::v0.11.pre
  23:        0x11008385f - middle::typeck::infer::lattice::CombineFields<'f>.CombineFieldsLatticeMethods::set_var_to_merged_bounds::h2086516640415841397::v0.11.pre
  24:        0x1100765a7 - middle::typeck::infer::sub::Sub<'f>.Combine::tys::h175f11cc5dc2597d0fm::v0.11.pre
  25:        0x11007a63c - middle::typeck::infer::sub::Sub<'f>.Combine::contratys::h22fafc5b276ecf36w6l::v0.11.pre
  26:        0x1100bfd65 - middle::typeck::infer::combine::eq_tys::closure.70748
  27:        0x110072bcc - middle::typeck::infer::InferCtxt<'a>::try::h18173051383935161273::v0.11.pre
  28:        0x1100bfc61 - middle::typeck::infer::combine::eq_tys::h14490634581668630721::v0.11.pre
  29:        0x1100be580 - middle::typeck::infer::combine::Combine::substs::h8806601970722992653::v0.11.pre
  30:        0x1100770c1 - middle::typeck::infer::sub::Sub<'f>.Combine::tys::h175f11cc5dc2597d0fm::v0.11.pre
  31:        0x1100c6e0b - middle::typeck::infer::coercion::Coerce<'f>::subtype::h62ea9fdfc572f0d8sfn::v0.11.pre
  32:        0x1100c6cb7 - middle::typeck::infer::coercion::Coerce<'f>::tys::closure.70831
  33:        0x1100c38d1 - middle::typeck::infer::coercion::Coerce<'f>::unpack_actual_value::h2dfaecaef773b72d1fn::v0.11.pre
  34:        0x1100c36cd - middle::typeck::infer::coercion::Coerce<'f>::tys::h2efd240de30beacfb8m::v0.11.pre
  35:        0x1100eac9d - middle::typeck::infer::mk_coercety::closure.71497
  36:        0x1100ea7d3 - middle::typeck::infer::InferCtxt<'a>::commit::closure.71487
  37:        0x1100e97e0 - util::common::indent::h14231954806218317178::v0.11.pre
  38:        0x1100ea5f4 - middle::typeck::infer::mk_coercety::closure.71483
  39:        0x1100e97e0 - util::common::indent::h14231954806218317178::v0.11.pre
  40:        0x110053613 - middle::typeck::infer::mk_coercety::h0c90b6b9e175a0187aq::v0.11.pre
  41:        0x110015da1 - middle::typeck::check::FnCtxt<'a>::mk_assignty::hb3de0ef94ed252baG59::v0.11.pre
  42:        0x110015c28 - middle::typeck::check::demand::coerce::h9b03fd3cf1701d89lS5::v0.11.pre
  43:        0x11005d25a - middle::typeck::check::check_expr_coercable_to_type::closure.69083
  44:        0x110054604 - middle::typeck::check::check_expr_with_unifier::h4e2897dbe4ea38cclIa::v0.11.pre
  45:        0x11005e31c - middle::typeck::check::check_expr_with_unifier::check_argument_types::h16c021d4d2f9109aAMa::v0.11.pre
  46:        0x11005965a - middle::typeck::check::check_expr_with_unifier::h4e2897dbe4ea38cclIa::v0.11.pre
  47:        0x110070413 - middle::typeck::check::check_stmt::hfaddb728054d31d4n3c::v0.11.pre
  48:        0x1100353d3 - middle::typeck::check::check_block_with_expected::hc40e54c79cbf136ak7c::v0.11.pre
  49:        0x110030c6a - middle::typeck::check::check_fn::h110e9312e887d6depv8::v0.11.pre
  50:        0x11003045a - middle::typeck::check::check_bare_fn::h63ca38b0c972d0e4Wk8::v0.11.pre
  51:        0x11002908f - middle::typeck::check::check_item::hb9ceb87f27759b1a0R8::v0.11.pre
  52:        0x1100301dd - middle::typeck::check::check_item_types::hb17499c25494b6f0ek8::v0.11.pre
  53:        0x1101683d6 - util::common::time::h17646179309215505883::v0.11.pre
  54:        0x11016744d - middle::typeck::check_crate::hc361b33fe1242173Qgw::v0.11.pre
  55:        0x110590529 - driver::driver::phase_3_run_analysis_passes::h0f47e246146a1253bei::v0.11.pre
  56:        0x110595fe2 - driver::driver::compile_input::h2c3dbe74f799efa1gEi::v0.11.pre
  57:        0x1105bc211 - run_compiler::h6db406e36b756e80saq::v0.11.pre
  58:        0x1105d3d8d - main_args::closure.93972
  59:        0x1105d2502 - monitor::closure.93850
  60:        0x1105cd05b - task::TaskBuilder::try::closure.93616
  61:        0x112163b6c - task::spawn_opts::closure.7397
  62:        0x112b2bc18 - rt::task::Task::run::closure.28413
  63:        0x112b4cb7c - rust_try
  64:        0x112b2ba97 - rt::task::Task::run::hf99ca2c1546bbfb0XqD::v0.11.pre
  65:        0x1121639ef - task::spawn_opts::closure.7369
  66:        0x112b32f16 - rt::thread::thread_start::h61d07f070734480188D::v0.11.pre
  67:     0x7fff90436899 - _pthread_body
  68:     0x7fff9043672a - _pthread_struct_init

[pnkfelix]

cc me. This may be blocking some work on Servo.

[nikomatsakis]

cc me

[pnkfelix]

Slightly simpler test case:

#![crate_type="lib"]

fn erickt_fn() {
    fn test2(_x: Option<|f: |g: &int||>) {}
    test2(Some(|_f: |g: &int|| {}));
}

Also, I found the problem goes away if you manually lift the closure types into type items, like so:

    #[cfg(show_erickt_bug)]
    fn erickt_fn() {
        fn test2(_x: Option<|y: Option<|z: &int|>|>) {}
        test2(Some(|_y: Option<|z: &int|>| {}));
    }
    #[cfg(not(show_erickt_bug))]
    fn erickt_fn() {
        type F1<'a> = |z: &'a int|:'a;
        type F2<'b> = |y: Option<F1<'b>>|:'b;
        fn test2<'c>(_x: Option<F2>) {}
        test2(Some(|_y| {}))
    }

This probably reflects some change where the lifetimes go from being late-bound to being early bound. The version with type items might not be handle cases that the version with inlined closure types can handle, I'm not 100% sure yet.

[nikomatsakis]

The type item versions are not equivalent because they don't have any bound lifetimes. 

Niko

-------- Original message --------
From: Felix S Klock II notifications@github.com
Date:06/18/2014 07:17 (GMT-05:00)
To: rust-lang/rust rust@noreply.github.com
Cc: Niko Matsakis niko@alum.mit.edu
Subject: Re: [rust] Trouble passing closures with borrowed pointers inside
options (#10846)

Slightly simpler test case:

#![crate_type="lib"]

fn erickt_fn() {
fn test2(_x: Option<|f: |g: &int||>) {}
test2(Some(|_f: |g: &int|| {}));
}
Also, I found the problem goes away if you manually lift the closure types into type items, like so:

#[cfg(show_erickt_bug)]
fn erickt_fn() {
    fn test2(_x: Option<|y: Option<|z: &int|>|>) {}
    test2(Some(|_y: Option<|z: &int|>| {}));
}
#[cfg(not(show_erickt_bug))]
fn erickt_fn() {
    type F1<'a> = |z: &'a int|:'a;
    type F2<'b> = |y: Option<F1<'b>>|:'b;
    fn test2<'c>(_x: Option<F2>) {}
    test2(Some(|_y| {}))
}

This probably reflects some change where the lifetimes go from being late-bound to being early bound. The version with type items might not be handle cases that the version with inlined closure types can handle, I'm not 100% sure yet.

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