ICE in traits using lifetime elision

[OtaK]

Hello,

The compiler panics when using this code:

pub struct TriggerICE<'a>(&'a str);
impl From<String> for TriggerICE<'_> {
    fn from(s: String) -> Self {
        TriggerICE(&s)
    }
}

You can check it out on the playground here: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=75ef6a4515e975e3ffafcd17373aa8b4

Thanks,

Have a good day

Meta

rustc --version --verbose:

rustc 1.31.0 (abe02cefd 2018-12-04)
binary: rustc
commit-hash: abe02cefd6cd1916df62ad7dc80161bea50b72e8
commit-date: 2018-12-04
host: x86_64-apple-darwin
release: 1.31.0
LLVM version: 8.0

Backtrace:

   Compiling playground v0.0.1 (/playground)
error: internal compiler error: librustc/hir/map/mod.rs:816: expected expr, found method from in <TriggerICE<'_> as std::convert::From<std::string::String>>::from (id=28)

thread 'main' panicked at 'Box<Any>', librustc_errors/lib.rs:600:9
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::print
             at libstd/sys_common/backtrace.rs:71
             at libstd/sys_common/backtrace.rs:59
   2: std::panicking::default_hook::{{closure}}
             at libstd/panicking.rs:211
   3: std::panicking::default_hook
             at libstd/panicking.rs:227
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
             at libstd/panicking.rs:480
   6: std::panicking::begin_panic
   7: rustc_errors::Handler::bug
   8: rustc::util::bug::opt_span_bug_fmt::{{closure}}
   9: rustc::ty::context::tls::with_opt::{{closure}}
  10: rustc::ty::context::tls::with_context_opt
  11: rustc::ty::context::tls::with_opt
  12: rustc::util::bug::opt_span_bug_fmt
  13: rustc::util::bug::bug_fmt
  14: rustc::hir::map::Map::expect_expr
  15: rustc_mir::borrow_check::nll::region_infer::error_reporting::region_name::<impl rustc_mir::borrow_check::nll::region_infer::RegionInferenceContext<'tcx>>::give_region_a_name
  16: rustc_mir::borrow_check::nll::region_infer::error_reporting::<impl rustc_mir::borrow_check::nll::region_infer::RegionInferenceContext<'tcx>>::free_region_constraint_info
  17: rustc_mir::borrow_check::nll::explain_borrow::<impl rustc_mir::borrow_check::MirBorrowckCtxt<'cx, 'gcx, 'tcx>>::explain_why_borrow_contains_point
  18: rustc_mir::borrow_check::error_reporting::<impl rustc_mir::borrow_check::MirBorrowckCtxt<'cx, 'gcx, 'tcx>>::report_borrowed_value_does_not_live_long_enough
  19: rustc_mir::borrow_check::path_utils::each_borrow_involving_path
  20: rustc_mir::borrow_check::MirBorrowckCtxt::access_place
  21: <rustc_mir::borrow_check::MirBorrowckCtxt<'cx, 'gcx, 'tcx> as rustc_mir::dataflow::DataflowResultsConsumer<'cx, 'tcx>>::visit_terminator_entry
  22: rustc_mir::borrow_check::do_mir_borrowck
  23: rustc::ty::context::tls::with_related_context
  24: rustc::infer::InferCtxtBuilder::enter
  25: rustc_mir::borrow_check::mir_borrowck
  26: rustc::ty::query::__query_compute::mir_borrowck
  27: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::mir_borrowck<'tcx>>::compute
  28: rustc::dep_graph::graph::DepGraph::with_task_impl
  29: <rustc::ty::query::plumbing::JobOwner<'a, 'tcx, Q>>::start
  30: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
  31: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
  32: rustc::ty::query::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::mir_borrowck
  33: rustc::ty::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::par_body_owners
  34: rustc::util::common::time
  35: rustc::ty::context::tls::enter_context
  36: <std::thread::local::LocalKey<T>>::with
  37: rustc::ty::context::TyCtxt::create_and_enter
  38: rustc_driver::driver::compile_input
  39: rustc_driver::run_compiler_with_pool
  40: rustc_driver::driver::spawn_thread_pool
  41: rustc_driver::run_compiler
  42: <scoped_tls::ScopedKey<T>>::set
  43: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
  44: __rust_maybe_catch_panic
             at libpanic_unwind/lib.rs:102
  45: rustc_driver::run
  46: rustc_driver::main
  47: std::rt::lang_start::{{closure}}
  48: std::panicking::try::do_call
             at libstd/rt.rs:59
             at libstd/panicking.rs:310
  49: __rust_maybe_catch_panic
             at libpanic_unwind/lib.rs:102
  50: std::rt::lang_start_internal
             at libstd/panicking.rs:289
             at libstd/panic.rs:392
             at libstd/rt.rs:58
  51: main
  52: __libc_start_main
  53: <unknown>
query stack during panic:
#0 [mir_borrowck] processing `<TriggerICE<'_> as std::convert::From<std::string::String>>::from`
end of query stack
error: aborting due to previous error


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 1.31.0 (abe02cefd 2018-12-04) running on x86_64-unknown-linux-gnu

note: compiler flags: -C codegen-units=1 -C debuginfo=2 --crate-type lib

note: some of the compiler flags provided by cargo are hidden

error: Could not compile `playground`.

To learn more, run the command again with --verbose.

[QuietMisdreavus]

According to the playground link, it looks like this has been fixed in beta and nightly.

[OtaK]

I should add that this code triggers the correct behavior on stable:

pub struct TriggerICE<'a>(&'a str);
impl<'a> From<String> for TriggerICE<'a> {
    fn from(s: String) -> Self {
        TriggerICE(&s)
    }
}

-->

   Compiling playground v0.0.1 (/playground)
error[E0515]: cannot return value referencing function parameter `s`
 --> src/main.rs:4:9
  |
4 |         TriggerICE(&s)
  |         ^^^^^^^^^^^--^
  |         |          |
  |         |          `s` is borrowed here
  |         returns a value referencing data owned by the current function

error: aborting due to previous error

For more information about this error, try `rustc --explain E0515`.
error: Could not compile `playground`.

To learn more, run the command again with --verbose.

Also, as Q noted above, it has been fixed altogether on beta and nightly channels indeed.

[pnkfelix]

i put "needstest" but actually this might just be a dupe of #55394, which would probably mean that the test added for PR #55822 suffices...

[pnkfelix]

yeah, reviewing PR #55822 and this code, my takeaway is that the test in #55822 suffices.