ICE(broken MIR and no errors despite delay_span_bug) when existential type alias is used as closure return value causing type error #74280
Description
Code
#![feature(min_type_alias_impl_trait)] #![feature(type_alias_impl_trait)] type Test = impl Copy; fn test() -> Test { let y = || -> Test { () }; 7 }Meta
rustc --version --verbose:
rustc 1.46.0-nightly (346aec9b0 2020-07-11) binary: rustc commit-hash: 346aec9b02f3c74f3fce97fd6bda24709d220e49 commit-date: 2020-07-11 host: x86_64-unknown-linux-gnu release: 1.46.0-nightly LLVM version: 10.0 Error output
warning: unused variable: `y` --> rust-ice.rs:6:9 | 6 | let y = || -> Test { () }; | ^ help: if this is intentional, prefix it with an underscore: `_y` | = note: `#[warn(unused_variables)]` on by default warning: type alias is never used: `Test` --> rust-ice.rs:3:1 | 3 | type Test = impl Copy; | ^^^^^^^^^^^^^^^^^^^^^^ | = note: `#[warn(dead_code)]` on by default warning: function is never used: `test` --> rust-ice.rs:5:4 | 5 | fn test() -> Test { | ^^^^ warning: 3 warnings emitted error: internal compiler error: broken MIR in DefId(0:5 ~ rust_ice[317d]::test[0]) (bb0[0]): equate_inputs_and_outputs: `impl std::marker::Copy==i32` failed with `NoSolution` --> rust-ice.rs:8:2 | 8 | } | ^ | = note: delayed at src/librustc_mir/borrow_check/type_check/mod.rs:258:27 Backtrace
thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', src/librustc_errors/lib.rs:367:17 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:217 10: rustc_driver::report_ice 11: std::panicking::rust_panic_with_hook at src/libstd/panicking.rs:530 12: std::panicking::begin_panic 13: <rustc_errors::HandlerInner as core::ops::drop::Drop>::drop 14: core::ptr::drop_in_place 15: <alloc::rc::Rc<T> as core::ops::drop::Drop>::drop 16: core::ptr::drop_in_place 17: rustc_span::with_source_map 18: rustc_interface::interface::create_compiler_and_run 19: scoped_tls::ScopedKey<T>::set note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace. 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 1.46.0-nightly (346aec9b0 2020-07-11) running on x86_64-unknown-linux-gnu query stack during panic: end of query stack