Cannot create local mono-item for DefId

[bobbobbio]

The following scenario used to work fine 1.25.0:

echo '
pub fn hello_world()
{
    println!("hello world");
}
' > bar.rs
echo '
extern crate bar;

pub fn foo()
{
    bar::hello_world();
}
' > foo.rs
rustc --crate-type rlib --emit metadata bar.rs
rustc --crate-type rlib --emit llvm-bc bar.rs
rustc --crate-type rlib --emit llvm-bc foo.rs -L .

This would create two .bc files that could be linked together into a program, but when I try this on 1.26.{0,1,2} the compiler crashes like so:

error: internal compiler error: librustc_mir/monomorphize/collector.rs:746: Cannot create local mono-item for DefId(11/0:3 ~ bar[8787]::hello_world[0])

thread 'rustc' panicked at 'Box<Any>', librustc_errors/lib.rs:543:9
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
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:207
   3: std::panicking::default_hook
             at libstd/panicking.rs:223
   4: core::ops::function::Fn::call
   5: std::panicking::rust_panic_with_hook
             at libstd/panicking.rs:403
   6: std::panicking::begin_panic
   7: rustc_errors::Handler::bug
   8: rustc::session::opt_span_bug_fmt::{{closure}}
   9: rustc::ty::context::tls::with_opt::{{closure}}
  10: <std::thread::local::LocalKey<T>>::try_with
  11: <std::thread::local::LocalKey<T>>::with
  12: rustc::ty::context::tls::with
  13: rustc::ty::context::tls::with_opt
  14: rustc::session::opt_span_bug_fmt
  15: rustc::session::bug_fmt
  16: rustc_mir::monomorphize::collector::should_monomorphize_locally
  17: rustc_mir::monomorphize::collector::visit_instance_use
  18: <rustc_mir::monomorphize::collector::MirNeighborCollector<'a, 'tcx> as rustc::mir::visit::Visitor<'tcx>>::visit_terminator_kind
  19: rustc_mir::monomorphize::collector::collect_items_rec
  20: rustc_mir::monomorphize::collector::collect_crate_mono_items
  21: rustc::util::common::time
  22: rustc_trans::base::collect_and_partition_translation_items
  23: rustc::dep_graph::graph::DepGraph::with_task_impl
  24: rustc_errors::Handler::track_diagnostics
  25: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::cycle_check
  26: rustc::ty::maps::<impl rustc::ty::maps::queries::collect_and_partition_translation_items<'tcx>>::force
  27: rustc::ty::maps::<impl rustc::ty::maps::queries::collect_and_partition_translation_items<'tcx>>::try_get
  28: rustc::ty::maps::TyCtxtAt::collect_and_partition_translation_items
  29: rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::collect_and_partition_translation_items
  30: rustc_trans::base::trans_crate
  31: <rustc_trans::LlvmTransCrate as rustc_trans_utils::trans_crate::TransCrate>::trans_crate
  32: rustc::util::common::time
  33: rustc_driver::driver::phase_4_translate_to_llvm
  34: rustc_driver::driver::compile_input::{{closure}}
  35: <std::thread::local::LocalKey<T>>::with
  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_impl
  40: syntax::with_globals
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 1.26.2 (594fb253c 2018-06-01) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type rlib

[peterhuene]

Possibly dupe/related to #50865?

[oli-obk]

Yea I think this is a dupe, handling over there

[bobbobbio]

The issue you mention seems to have something to do with impl trait (and looks like it goes away when the use is removed?) , whereas the issue I posted here crashes with even the simplest rust code. Are they really the same?

[oli-obk]

Hmm... you're right. I mean impl Trait in the other issue is just the trigger, the cause is in a normal function calling another one, but here you have another crate

[bobbobbio]

I've discovered that if I tell the compiler to emit another type along with metadata like --emit=link,metadata this issue goes away. It makes me suspect this piece of code in librustc/session/config.rs:

    // True if any of the output types require codegen or linking.
    pub fn should_codegen(&self) -> bool {
        self.0.keys().any(|k| match *k {
            OutputType::Bitcode
            | OutputType::Assembly
            | OutputType::LlvmAssembly
            | OutputType::Mir
            | OutputType::Object
            | OutputType::Exe => true,
            OutputType::Metadata | OutputType::DepInfo => false,
        })
    }

I'm wondering if by not running the code-gen or linking when outputting the metadata is causing this.

[estebank]

Triage: still repros:

error: internal compiler error: src/librustc_mir/monomorphize/collector.rs:802: cannot create local mono-item for DefId(15:3 ~ bar[8787]::hello_world[0])

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:892:9
stack backtrace:
   0: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
   1: core::fmt::write
   2: std::io::Write::write_fmt
   3: std::panicking::default_hook::{{closure}}
   4: std::panicking::default_hook
   5: rustc_driver::report_ice
   6: std::panicking::rust_panic_with_hook
   7: std::panicking::begin_panic
   8: rustc_errors::HandlerInner::bug
   9: rustc_errors::Handler::bug
  10: rustc::util::bug::opt_span_bug_fmt::{{closure}}
  11: rustc::ty::context::tls::with_opt::{{closure}}
  12: rustc::ty::context::tls::with_context_opt
  13: rustc::ty::context::tls::with_opt
  14: rustc::util::bug::opt_span_bug_fmt
  15: rustc::util::bug::bug_fmt
  16: rustc_mir::monomorphize::collector::should_monomorphize_locally
  17: rustc_mir::monomorphize::collector::visit_instance_use
  18: <rustc_mir::monomorphize::collector::MirNeighborCollector as rustc::mir::visit::Visitor>::visit_terminator_kind
  19: rustc::mir::visit::Visitor::visit_body
  20: rustc_mir::monomorphize::collector::collect_items_rec
  21: rustc_mir::monomorphize::collector::collect_crate_mono_items::{{closure}}
  22: rustc::util::common::time
  23: rustc_mir::monomorphize::collector::collect_crate_mono_items
  24: rustc::util::common::time
  25: rustc_mir::monomorphize::partitioning::collect_and_partition_mono_items
  26: rustc::ty::query::__query_compute::collect_and_partition_mono_items
  27: rustc::dep_graph::graph::DepGraph::with_task_impl
  28: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  29: rustc_codegen_ssa::back::symbol_export::exported_symbols_provider_local
  30: rustc::ty::query::__query_compute::exported_symbols
  31: rustc::dep_graph::graph::DepGraph::with_task_impl
  32: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  33: rustc_metadata::rmeta::encoder::EncodeContext::encode_crate_root
  34: rustc::ty::context::tls::with_context::{{closure}}
  35: rustc_metadata::rmeta::encoder::encode_metadata
  36: rustc_metadata::rmeta::decoder::cstore_impl::<impl rustc::middle::cstore::CrateStore for rustc_metadata::creader::CStore>::encode_metadata
  37: rustc::ty::context::TyCtxt::encode_metadata
  38: rustc_interface::passes::encode_and_write_metadata
  39: rustc::util::common::time
  40: rustc_interface::passes::start_codegen
  41: rustc::ty::context::tls::enter_global
  42: rustc_interface::queries::Query<T>::compute
  43: rustc_interface::queries::Queries::ongoing_codegen
  44: rustc_interface::interface::run_compiler_in_existing_thread_pool
  45: std::thread::local::LocalKey<T>::with
  46: scoped_tls::ScopedKey<T>::set
  47: syntax::with_globals