rustdoc: ICE: synthetic auto trait impls: `no region_name found` involving user-written impl that applies to higher-ranked lifetimes

[fmease]

Reproducer

pub struct Outer<'a>(Local<fn(&'a ())>);

struct Local<T>(T);

impl std::marker::Unpin for Local<for<'a> fn(&'a ())> {}

Compiler Output

thread 'rustc' panicked at src/librustdoc/clean/auto_trait.rs:222:52:
no region_name found
stack backtrace:
   0:     0x7f08e138bfa5 - std::backtrace_rs::backtrace::libunwind::trace::h78f4e9a1eb03772b
                               at /rustc/85e449a3237e82c9ade8936a82bd4fc64cfe1057/library/std/src/../../backtrace/src/backtrace/libunwind.rs:105:5
   1:     0x7f08e138bfa5 - std::backtrace_rs::backtrace::trace_unsynchronized::h3a38e307e09f41a8
                               at /rustc/85e449a3237e82c9ade8936a82bd4fc64cfe1057/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f08e138bfa5 - std::sys_common::backtrace::_print_fmt::he3d0e690b8551c2a
                               at /rustc/85e449a3237e82c9ade8936a82bd4fc64cfe1057/library/std/src/sys_common/backtrace.rs:68:5
   3:     0x7f08e138bfa5 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h1fad2a971ec36506
                               at /rustc/85e449a3237e82c9ade8936a82bd4fc64cfe1057/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f08e13dcfeb - core::fmt::rt::Argument::fmt::h7012a9e731998987
                               at /rustc/85e449a3237e82c9ade8936a82bd4fc64cfe1057/library/core/src/fmt/rt.rs:142:9
   5:     0x7f08e13dcfeb - core::fmt::write::h93b67068392b644b
                               at /rustc/85e449a3237e82c9ade8936a82bd4fc64cfe1057/library/core/src/fmt/mod.rs:1153:17
   6:     0x7f08e1380d3f - std::io::Write::write_fmt::he9d9e4eda6dbe3e6
                               at /rustc/85e449a3237e82c9ade8936a82bd4fc64cfe1057/library/std/src/io/mod.rs:1843:15
   7:     0x7f08e138bd7e - std::sys_common::backtrace::_print::h476d4a31909fadf9
                               at /rustc/85e449a3237e82c9ade8936a82bd4fc64cfe1057/library/std/src/sys_common/backtrace.rs:47:5
   8:     0x7f08e138bd7e - std::sys_common::backtrace::print::h1fb17543fdb8f09d
                               at /rustc/85e449a3237e82c9ade8936a82bd4fc64cfe1057/library/std/src/sys_common/backtrace.rs:34:9
   9:     0x7f08e138e9f9 - std::panicking::default_hook::{{closure}}::h6fc8d175caf3dd11
  10:     0x7f08e138e763 - std::panicking::default_hook::h29dd20611e406ef6
                               at /rustc/85e449a3237e82c9ade8936a82bd4fc64cfe1057/library/std/src/panicking.rs:292:9
  11:     0x7f08e43ca26f - std[7e22d6a0f2697500]::panicking::update_hook::<alloc[cc0f79cfb0d5dfba]::boxed::Box<rustc_driver_impl[6402987c68c0a870]::install_ice_hook::{closure#0}>>::{closure#0}
  12:     0x7f08e138f150 - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h611aa430b073f4d2
                               at /rustc/85e449a3237e82c9ade8936a82bd4fc64cfe1057/library/alloc/src/boxed.rs:2029:9
  13:     0x7f08e138f150 - std::panicking::rust_panic_with_hook::h1aef15bad4c9dc6b
                               at /rustc/85e449a3237e82c9ade8936a82bd4fc64cfe1057/library/std/src/panicking.rs:783:13
  14:     0x7f08e138eea6 - std::panicking::begin_panic_handler::{{closure}}::h820c595fe343fedf
                               at /rustc/85e449a3237e82c9ade8936a82bd4fc64cfe1057/library/std/src/panicking.rs:657:13
  15:     0x7f08e138c469 - std::sys_common::backtrace::__rust_end_short_backtrace::h5f5dad5c075b596d
                               at /rustc/85e449a3237e82c9ade8936a82bd4fc64cfe1057/library/std/src/sys_common/backtrace.rs:171:18
  16:     0x7f08e138ebd7 - rust_begin_unwind
                               at /rustc/85e449a3237e82c9ade8936a82bd4fc64cfe1057/library/std/src/panicking.rs:645:5
  17:     0x7f08e13d9486 - core::panicking::panic_fmt::hd12a49b253347127
                               at /rustc/85e449a3237e82c9ade8936a82bd4fc64cfe1057/library/core/src/panicking.rs:72:14
  18:     0x7f08e13d963c - core::panicking::panic_display::h5ead28ef6bb2b7dd
                               at /rustc/85e449a3237e82c9ade8936a82bd4fc64cfe1057/library/core/src/panicking.rs:193:5
  19:     0x7f08e13d924c - core::panicking::panic_str::hbc8176a12d958e35
                               at /rustc/85e449a3237e82c9ade8936a82bd4fc64cfe1057/library/core/src/panicking.rs:168:5
  20:     0x7f08e13d924c - core::option::expect_failed::h9309a723997892d7
                               at /rustc/85e449a3237e82c9ade8936a82bd4fc64cfe1057/library/core/src/option.rs:1994:5
  21:     0x55fe23356e96 - <rustc_trait_selection[ba26e62bc53f9bdc]::traits::auto_trait::AutoTraitFinder>::find_auto_trait_generics::<rustdoc[653978f5a7bdea11]::clean::types::Generics, <rustdoc[653978f5a7bdea11]::clean::auto_trait::AutoTraitFinder>::generate_for_trait::{closure#0}>
  22:     0x55fe234b9b50 - <rustdoc[653978f5a7bdea11]::clean::auto_trait::AutoTraitFinder>::generate_for_trait
  23:     0x55fe234d7b81 - rustdoc[653978f5a7bdea11]::clean::utils::get_auto_trait_and_blanket_impls
  24:     0x55fe235e483a - <rustdoc[653978f5a7bdea11]::passes::collect_trait_impls::SyntheticImplCollector as rustdoc[653978f5a7bdea11]::visit::DocVisitor>::visit_item
  25:     0x55fe235e4b7a - <rustdoc[653978f5a7bdea11]::passes::collect_trait_impls::SyntheticImplCollector as rustdoc[653978f5a7bdea11]::visit::DocVisitor>::visit_item
  26:     0x55fe235e133d - rustdoc[653978f5a7bdea11]::passes::collect_trait_impls::collect_trait_impls
  27:     0x55fe2350a9fd - rustdoc[653978f5a7bdea11]::core::run_global_ctxt
  28:     0x55fe2340bcef - <rustc_middle[2a1b38579ffd754c]::ty::context::GlobalCtxt>::enter::<rustdoc[653978f5a7bdea11]::main_args::{closure#1}::{closure#0}::{closure#0}, core[40640d3ebf5fb0ac]::result::Result<(), rustc_span[e4a18c9710c4bc6]::ErrorGuaranteed>>::{closure#0}
  29:     0x55fe23415983 - rustc_interface[de4b62a04c0361df]::interface::run_compiler::<core[40640d3ebf5fb0ac]::result::Result<(), rustc_span[e4a18c9710c4bc6]::ErrorGuaranteed>, rustdoc[653978f5a7bdea11]::main_args::{closure#1}>::{closure#0}
  30:     0x55fe233e1a31 - std[7e22d6a0f2697500]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[de4b62a04c0361df]::util::run_in_thread_with_globals<rustc_interface[de4b62a04c0361df]::util::run_in_thread_pool_with_globals<rustc_interface[de4b62a04c0361df]::interface::run_compiler<core[40640d3ebf5fb0ac]::result::Result<(), rustc_span[e4a18c9710c4bc6]::ErrorGuaranteed>, rustdoc[653978f5a7bdea11]::main_args::{closure#1}>::{closure#0}, core[40640d3ebf5fb0ac]::result::Result<(), rustc_span[e4a18c9710c4bc6]::ErrorGuaranteed>>::{closure#0}, core[40640d3ebf5fb0ac]::result::Result<(), rustc_span[e4a18c9710c4bc6]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[40640d3ebf5fb0ac]::result::Result<(), rustc_span[e4a18c9710c4bc6]::ErrorGuaranteed>>
  31:     0x55fe2341f1c6 - <<std[7e22d6a0f2697500]::thread::Builder>::spawn_unchecked_<rustc_interface[de4b62a04c0361df]::util::run_in_thread_with_globals<rustc_interface[de4b62a04c0361df]::util::run_in_thread_pool_with_globals<rustc_interface[de4b62a04c0361df]::interface::run_compiler<core[40640d3ebf5fb0ac]::result::Result<(), rustc_span[e4a18c9710c4bc6]::ErrorGuaranteed>, rustdoc[653978f5a7bdea11]::main_args::{closure#1}>::{closure#0}, core[40640d3ebf5fb0ac]::result::Result<(), rustc_span[e4a18c9710c4bc6]::ErrorGuaranteed>>::{closure#0}, core[40640d3ebf5fb0ac]::result::Result<(), rustc_span[e4a18c9710c4bc6]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[40640d3ebf5fb0ac]::result::Result<(), rustc_span[e4a18c9710c4bc6]::ErrorGuaranteed>>::{closure#1} as core[40640d3ebf5fb0ac]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  32:     0x7f08e1398919 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hb3b7a92ba6819109
                               at /rustc/85e449a3237e82c9ade8936a82bd4fc64cfe1057/library/alloc/src/boxed.rs:2015:9
  33:     0x7f08e1398919 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hbb9c447d7e0122c8
                               at /rustc/85e449a3237e82c9ade8936a82bd4fc64cfe1057/library/alloc/src/boxed.rs:2015:9
  34:     0x7f08e1398919 - std::sys::pal::unix::thread::Thread::new::thread_start::h7868674606c7eb25
                               at /rustc/85e449a3237e82c9ade8936a82bd4fc64cfe1057/library/std/src/sys/pal/unix/thread.rs:108:17
  35:     0x7f08e10939eb - <unknown>
  36:     0x7f08e11177cc - <unknown>
  37:                0x0 - <unknown>

error: the compiler unexpectedly panicked. this is a bug.

note: it seems that this compiler `1.79.0-nightly (85e449a32 2024-03-22)` is outdated, a newer nightly should have been released in the mean time
  |
  = note: please consider running `rustup update nightly` to update the nightly channel and check if this problem still persists
  = note: if the problem still persists, we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-rustdoc&template=ice.md

note: please attach the file at `/home/fmease/programming/rust2/rustc-ice-2024-03-31T19_57_39-248620.txt` to your bug report

query stack during panic:
end of query stack

Alternative Reproducer

Conceptually simpler but requires the use of unstable features:

#![feature(auto_traits)]

pub struct Outer<'a>(fn(&'a ()));

impl U for for<'a> fn(&'a ()) {}

pub auto trait U {}

Identical compiler output.

Meta

rustdoc -Vv:

rustc 1.79.0-nightly (85e449a32 2024-03-22)
binary: rustc
commit-hash: 85e449a3237e82c9ade8936a82bd4fc64cfe1057
commit-date: 2024-03-22
host: x86_64-unknown-linux-gnu
release: 1.79.0-nightly
LLVM version: 18.1.2

[fmease]

And no, we ought not change region_name(region) to region.get_name(). Better reproducer that would fail even if we did that:

pub struct Outer<'a>(Local<fn(&'a ())>);

struct Local<T>(T);

impl std::marker::Unpin for Local<for<'x> fn(&'x ())> {}