rustc panic when running `cargo doc` in AutoTraitFinder::find_auto_trait_generics

[alexheretic]

rustc panic when running cargo doc. The crate otherwise seems to test, run & work fine.

Steps to reproduce

• Checkout https://github.com/alexheretic/glyph-brush rev ca74e6a25b26eed68b9513363bb45167a3729cd3.
• Run cargo doc -p glyph_brush_layout.

Meta

rustc --version --verbose:

rustc 1.43.1 (8d69840ab 2020-05-04)
binary: rustc
commit-hash: 8d69840ab92ea7f4d323420088dd8c9775f180cd
commit-date: 2020-05-04
host: x86_64-unknown-linux-gnu
release: 1.43.1
LLVM version: 9.0

Error output

thread 'rustc' panicked at 'Unable to fulfill trait DefId(2:1922 ~ core[cba4]::marker[0]::Unpin[0]) for 'lines::Lines<'a, 'b, L, F, S>': [FulfillmentError(Obligation(predicate=Binder(ProjectionPredicate(ProjectionTy { substs: [S], item_def_id: DefId(2:4774 ~ core[cba4]::iter[0]::traits[0]::iterator[0]::Iterator[0]::Item[0]) }, section::SectionText<'_>)), depth=3),Ambiguity)]', <::std::macros::panic macros>:5:6

Backtrace

stack backtrace:
   0:     0x7f0aaae0de84 - backtrace::backtrace::libunwind::trace::h5d52ba5f20882f09
                               at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.44/src/backtrace/libunwind.rs:86
   1:     0x7f0aaae0de84 - backtrace::backtrace::trace_unsynchronized::hceee092869668a74
                               at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.44/src/backtrace/mod.rs:66
   2:     0x7f0aaae0de84 - std::sys_common::backtrace::_print_fmt::ha312c2904605e4d5
                               at src/libstd/sys_common/backtrace.rs:78
   3:     0x7f0aaae0de84 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h5b9981092140b727
                               at src/libstd/sys_common/backtrace.rs:59
   4:     0x7f0aaae4687c - core::fmt::write::h5f6d7d8de88b4173
                               at src/libcore/fmt/mod.rs:1063
   5:     0x7f0aaadffba3 - std::io::Write::write_fmt::h893169117de3cc15
                               at src/libstd/io/mod.rs:1426
   6:     0x7f0aaae12cb5 - std::sys_common::backtrace::_print::h8ab61d4120f7a335
                               at src/libstd/sys_common/backtrace.rs:62
   7:     0x7f0aaae12cb5 - std::sys_common::backtrace::print::h8aae19fbb153bf2a
                               at src/libstd/sys_common/backtrace.rs:49
   8:     0x7f0aaae12cb5 - std::panicking::default_hook::{{closure}}::h1ee5b7d8b6f83429
                               at src/libstd/panicking.rs:204
   9:     0x7f0aaae12a02 - std::panicking::default_hook::hd6c32c13403f9210
                               at src/libstd/panicking.rs:224
  10:     0x7f0aaae13312 - std::panicking::rust_panic_with_hook::h1f2449d529a25f22
                               at src/libstd/panicking.rs:470
  11:     0x7f0aaae12efb - rust_begin_unwind
                               at src/libstd/panicking.rs:378
  12:     0x7f0aaae12e6b - std::panicking::begin_panic_fmt::h7c14cf40a8be97ee
                               at src/libstd/panicking.rs:332
  13:     0x555ec9c66980 - rustc_infer::traits::auto_trait::AutoTraitFinder::find_auto_trait_generics::{{closure}}::{{closure}}::h23db3ac7fd6e843f
  14:     0x555ec9cb8091 - rustc::ty::context::GlobalCtxt::enter_local::hfe81f864ff343900
  15:     0x555ec9c46955 - rustc_infer::traits::auto_trait::AutoTraitFinder::find_auto_trait_generics::h36f309d537b9b31c
  16:     0x555ec9d17313 - core::ops::function::impls::<impl core::ops::function::FnMut<A> for &mut F>::call_mut::h326df7d27ac162b5
  17:     0x555ec9cf5e35 - <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T,I>>::from_iter::h7b5dcf28f857e9fa
  18:     0x555ec9b179d5 - rustdoc::clean::utils::get_auto_trait_and_blanket_impls::h30f520b33c4ebe41
  19:     0x555ec9b26fd2 - <rustdoc::passes::collect_trait_impls::SyntheticImplCollector as rustdoc::fold::DocFolder>::fold_item::h09f2b172cfcdd88b
  20:     0x555ec9cece7e - <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T,I>>::from_iter::hcda28ada9930131c
  21:     0x555ec9b1976c - rustdoc::fold::DocFolder::fold_inner_recur::h1ebc268f1a5af5b2
  22:     0x555ec9b26ccd - <rustdoc::passes::collect_trait_impls::SyntheticImplCollector as rustdoc::fold::DocFolder>::fold_item::h09f2b172cfcdd88b
  23:     0x555ec9cece7e - <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T,I>>::from_iter::hcda28ada9930131c
  24:     0x555ec9b1976c - rustdoc::fold::DocFolder::fold_inner_recur::h1ebc268f1a5af5b2
  25:     0x555ec9b26ccd - <rustdoc::passes::collect_trait_impls::SyntheticImplCollector as rustdoc::fold::DocFolder>::fold_item::h09f2b172cfcdd88b
  26:     0x555ec9b249a8 - rustdoc::passes::collect_trait_impls::collect_trait_impls::hb96a767adeb24e06
  27:     0x555ec9b42a5d - rustc::ty::context::tls::enter_global::hbf719a8808dffc33
  28:     0x555ec9d15c61 - rustc_interface::interface::run_compiler_in_existing_thread_pool::hbfb381d6a6b1c5d8
  29:     0x555ec9cc006c - rustdoc::core::run_core::h3e13637dfb5154dd
  30:     0x555ec9b292d0 - <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once::ha269444829893481
  31:     0x555ec9b6457b - std::panicking::try::do_call::h3fc76fb3531c3219
  32:     0x7f0aaae246b7 - __rust_maybe_catch_panic
                               at src/libpanic_unwind/lib.rs:86
  33:     0x555ec9b2a34b - rustc_driver::catch_fatal_errors::h7a280b9cdf28f352
  34:     0x555ec9af56fd - rustdoc::main_options::h42dedd41a78b0329
  35:     0x555ec9b60a57 - scoped_tls::ScopedKey<T>::set::ha6b8c3cc8b8d950f
  36:     0x555ec9cb99e4 - rustc_ast::attr::with_globals::he8fa93d7ebdc5344
  37:     0x555ec9ac5492 - std::sys_common::backtrace::__rust_begin_short_backtrace::h291078985b95d359
  38:     0x7f0aaae246b7 - __rust_maybe_catch_panic
                               at src/libpanic_unwind/lib.rs:86
  39:     0x555ec9b66ca6 - core::ops::function::FnOnce::call_once{{vtable.shim}}::hc250b6ab2be39f01
  40:     0x7f0aaadef64f - <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once::h36e46972b1b7f7b7
                               at /rustc/8d69840ab92ea7f4d323420088dd8c9775f180cd/src/liballoc/boxed.rs:1017
  41:     0x7f0aaae22fbd - <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once::hdde89c32ce6999de
                               at /rustc/8d69840ab92ea7f4d323420088dd8c9775f180cd/src/liballoc/boxed.rs:1017
  42:     0x7f0aaae22fbd - std::sys_common::thread::start_thread::h5ae3fdd4dad03dd5
                               at src/libstd/sys_common/thread.rs:13
  43:     0x7f0aaae22fbd - std::sys::unix::thread::Thread::new::thread_start::h76b2403b2434c4c0
                               at src/libstd/sys/unix/thread.rs:80
  44:     0x7f0aaad4c422 - start_thread
  45:     0x7f0aaac5fb83 - __GI___clone
  46:                0x0 - <unknown>
error: Could not document `glyph_brush_layout`

[hellow554]

somewhat minified:

struct Lines<'a, L>
where
    L: Iterator<Item = &'a ()>,
{
    words: std::iter::Peekable<Words<'a, L>>,
}

struct Words<'a, L> {
    _m: std::marker::PhantomData<&'a L>,
}   

impl<'a, L> Iterator for Words<'a, L>
where
    L: Iterator<Item = &'a ()>,
{
    type Item = ();
    
    fn next(&mut self) -> Option<Self::Item> {
        unimplemented!()
    }
}

[hellow554]

Somewhat interesting:

nightly-2018-01-17 gives me:

 ✗ cargo doc  
 Documenting foo v0.1.0 (file:///tmp/tmp.NxnOdGgulp/foo)
error[E0309]: the parameter type `L` may not live long enough
 --> src/lib.rs:9:5
  |
8 | struct Words<'a, L> {
  |                  - help: consider adding an explicit lifetime bound `L: 'a`...
9 |     _m: std::marker::PhantomData<&'a L>,
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
note: ...so that the reference type `&'a L` does not outlive the data it points at
 --> src/lib.rs:9:5
  |
9 |     _m: std::marker::PhantomData<&'a L>,
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

and cargo check as gives me the same error message.

On nightly-2019-01-17 on the other hand cargo doc panics and cargo check does not complain any more:

✗ cargo check
    Checking foo v0.1.0 (/tmp/tmp.NxnOdGgulp/foo)
warning: struct is never constructed: `Lines`
 --> src/lib.rs:1:1
  |
1 | / struct Lines<'a, L>
2 | | where
3 | |     L: Iterator<Item = &'a ()>,
4 | | {
5 | |     words: std::iter::Peekable<Words<'a, L>>,
6 | | }
  | |_^
  |
  = note: #[warn(dead_code)] on by default

warning: struct is never constructed: `Words`
 --> src/lib.rs:8:1
  |
8 | struct Words<'a, L> {
  | ^^^^^^^^^^^^^^^^^^^

Edit: nightly-2018-12-01 gives me exactly no output. No warning, no ICE. That is weird as well...

[hellow554]

Regression in nightly-2018-12-08 (14997d5...4a45578) (nightly-2018-12-07 is not available)

The "no output" regression (from rejecting the program as such and giving no output at all) is in nightly-2018-09-13 (2f1547c...f2302da)

[jonas-schievink]

The latter is an intended change caused by #53793

[alexheretic]

This is still occurring, the panic seems to come from this line in AutoTraitFinder::find_auto_trait_generics.

Updated info:

rustc --version --verbose:

rustc 1.45.1 (c367798cf 2020-07-26)
binary: rustc
commit-hash: c367798cfd3817ca6ae908ce675d1d99242af148
commit-date: 2020-07-26
host: x86_64-unknown-linux-gnu
release: 1.45.1
LLVM version: 10.0

Error output

thread 'rustc' panicked at 'Unable to fulfill trait DefId(2:1944 ~ core[6c88]::marker[0]::Unpin[0]) for 'lines::Lines<'a, 'b, L, F, S>': [FulfillmentError(Obligation(predicate=Binder(ProjectionPredicate(ProjectionTy { substs: [S], item_def_id: DefId(2:4966 ~ core[6c88]::iter[0]::traits[0]::iterator[0]::Iterator[0]::Item[0]) }, section::SectionText<'_>)), depth=3),Ambiguity)]', /rustc/c367798cfd3817ca6ae908ce675d1d99242af148/src/libstd/macros.rs:16:9

Backtrace

thread 'rustc' panicked at 'Unable to fulfill trait DefId(2:1944 ~ core[6c88]::marker[0]::Unpin[0]) for 'lines::Lines<'a, 'b, L, F, S>': [FulfillmentError(Obligation(predicate=Binder(ProjectionPredicate(ProjectionTy { substs: [S], item_def_id: DefId(2:4966 ~ core[6c88]::iter[0]::traits[0]::iterator[0]::Iterator[0]::Item[0]) }, section::SectionText<'_>)), depth=3),Ambiguity)]', /rustc/c367798cfd3817ca6ae908ce675d1d99242af148/src/libstd/macros.rs:16:9
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/libunwind.rs:86
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print_fmt
             at src/libstd/sys_common/backtrace.rs:78
   3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
             at src/libstd/sys_common/backtrace.rs:59
   4: core::fmt::write
             at src/libcore/fmt/mod.rs:1076
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1537
   6: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:62
   7: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:49
   8: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:198
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:218
  10: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:486
  11: rust_begin_unwind
             at src/libstd/panicking.rs:388
  12: std::panicking::begin_panic_fmt
             at src/libstd/panicking.rs:342
  13: rustc_trait_selection::traits::auto_trait::AutoTraitFinder::find_auto_trait_generics::{{closure}}::{{closure}}
  14: rustc_middle::ty::context::GlobalCtxt::enter_local
  15: rustc_trait_selection::traits::auto_trait::AutoTraitFinder::find_auto_trait_generics
  16: core::ops::function::impls::<impl core::ops::function::FnMut<A> for &mut F>::call_mut
  17: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T,I>>::from_iter
  18: rustdoc::clean::utils::get_auto_trait_and_blanket_impls
  19: <rustdoc::passes::collect_trait_impls::SyntheticImplCollector as rustdoc::fold::DocFolder>::fold_item
  20: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T,I>>::from_iter
  21: rustdoc::fold::DocFolder::fold_inner_recur
  22: <rustdoc::passes::collect_trait_impls::SyntheticImplCollector as rustdoc::fold::DocFolder>::fold_item
  23: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T,I>>::from_iter
  24: rustdoc::fold::DocFolder::fold_inner_recur
  25: <rustdoc::passes::collect_trait_impls::SyntheticImplCollector as rustdoc::fold::DocFolder>::fold_item
  26: rustdoc::passes::collect_trait_impls::collect_trait_impls
  27: rustc_middle::ty::context::tls::enter_global
  28: rustc_interface::interface::run_compiler_in_existing_thread_pool
  29: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
  30: rustc_driver::catch_fatal_errors
  31: rustdoc::main_options
  32: scoped_tls::ScopedKey<T>::set
  33: rustc_ast::attr::with_globals
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
error: Could not document `glyph_brush_layout`.

[spastorino]

Assigning P-high as discussed as part of the Prioritization Working Group procedure and removing I-prioritize.