Rustc panic when building bobbin-sdk

[N5FPP]

While attempting to build the current bobbin-sdk under Ubuntu 18.04 using rust 1.34.0-nightly (02c4c28 2019-02-26) I get a panic in rustc.

$ RUST_BACKTRACE=1 make
...
cargo build
   Compiling bobbin-hz v0.1.0 (/home/pascal/Workspaces/Rust/STM32/bobbin-sdk/lib/bobbin-hz)
thread 'rustc' panicked at 'called `Option::unwrap()` on a `None` value', src/libcore/option.rs:345:21
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:39
   1: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:70
   2: std::panicking::default_hook::{{closure}}
             at src/libstd/sys_common/backtrace.rs:58
             at src/libstd/panicking.rs:200
   3: std::panicking::default_hook
             at src/libstd/panicking.rs:215
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:482
   6: std::panicking::continue_panic_fmt
             at src/libstd/panicking.rs:385
   7: rust_begin_unwind
             at src/libstd/panicking.rs:312
   8: core::panicking::panic_fmt
             at src/libcore/panicking.rs:85
   9: core::panicking::panic
             at src/libcore/panicking.rs:49
  10: rustc_mir::interpret::place::<impl rustc_mir::interpret::eval_context::EvalContext<'a, 'mir, 'tcx, M>>::ref_to_mplace
  11: rustc_mir::interpret::place::<impl rustc_mir::interpret::eval_context::EvalContext<'a, 'mir, 'tcx, M>>::deref_operand
  12: rustc_mir::interpret::place::<impl rustc_mir::interpret::eval_context::EvalContext<'a, 'mir, 'tcx, M>>::place_projection
  13: rustc_mir::interpret::place::<impl rustc_mir::interpret::eval_context::EvalContext<'a, 'mir, 'tcx, M>>::eval_place
  14: rustc_mir::interpret::step::<impl rustc_mir::interpret::eval_context::EvalContext<'a, 'mir, 'tcx, M>>::run
  15: rustc_mir::const_eval::eval_body_using_ecx
  16: rustc_mir::const_eval::const_eval_raw_provider
  17: rustc::ty::query::__query_compute::const_eval_raw
  18: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::const_eval_raw<'tcx>>::compute
  19: rustc::dep_graph::graph::DepGraph::with_task_impl
  20: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
  21: rustc_mir::const_eval::const_eval_provider
  22: rustc::ty::query::__query_compute::const_eval
  23: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::const_eval<'tcx>>::compute
  24: rustc::dep_graph::graph::DepGraph::with_task_impl
  25: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
  26: rustc_mir::const_eval::const_eval_provider
  27: rustc::ty::query::__query_compute::const_eval
  28: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::const_eval<'tcx>>::compute
  29: rustc::dep_graph::graph::DepGraph::with_task_impl
  30: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
  31: rustc_mir::monomorphize::collector::collect_items_rec
  32: rustc_mir::monomorphize::collector::collect_crate_mono_items::{{closure}}
  33: rustc::util::common::time
  34: rustc_mir::monomorphize::collector::collect_crate_mono_items
  35: rustc::util::common::time
  36: rustc_mir::monomorphize::partitioning::collect_and_partition_mono_items
  37: rustc::ty::query::__query_compute::collect_and_partition_mono_items
  38: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::collect_and_partition_mono_items<'tcx>>::compute
  39: rustc::dep_graph::graph::DepGraph::with_task_impl
  40: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
  41: rustc_codegen_ssa::back::symbol_export::exported_symbols_provider_local
  42: rustc::ty::query::__query_compute::exported_symbols
  43: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::exported_symbols<'tcx>>::compute
  44: rustc::dep_graph::graph::DepGraph::with_task_impl
  45: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
  46: rustc_metadata::encoder::encode_metadata
  47: rustc_metadata::cstore_impl::<impl rustc::middle::cstore::CrateStore for rustc_metadata::cstore::CStore>::encode_metadata
  48: rustc::ty::context::TyCtxt::encode_metadata
  49: rustc_codegen_llvm::base::write_metadata
  50: rustc::util::common::time
  51: rustc_codegen_ssa::base::codegen_crate
  52: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_utils::codegen_backend::CodegenBackend>::codegen_crate
  53: rustc::util::common::time
  54: rustc_driver::driver::phase_4_codegen
  55: rustc_driver::driver::compile_input::{{closure}}
  56: <std::thread::local::LocalKey<T>>::with
  57: rustc::ty::context::TyCtxt::create_and_enter
  58: rustc_driver::driver::compile_input
  59: rustc_driver::run_compiler_with_pool
  60: <scoped_tls::ScopedKey<T>>::set
  61: rustc_driver::run_compiler
  62: syntax::with_globals
  63: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:87
  64: <F as alloc::boxed::FnBox<A>>::call_box
  65: std::sys::unix::thread::Thread::new::thread_start
             at /rustc/02c4c28920ddfdb43e68a363b7fe59ac4c92399c/src/liballoc/boxed.rs:759
             at src/libstd/sys_common/thread.rs:14
             at src/libstd/sys/unix/thread.rs:81
  66: start_thread
  67: __clone
query stack during panic:
#0 [const_eval_raw] const-evaluating `Hz::as_u32`
#1 [const_eval] const-evaluating + checking `Hz::as_u32`
#2 [const_eval] const-evaluating + checking `Hz::as_u32`
#3 [collect_and_partition_mono_items] collect_and_partition_mono_items
#4 [exported_symbols] exported_symbols
end of query stack

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 1.34.0-nightly (02c4c2892 2019-02-26) running on x86_64-unknown-linux-gnu

note: compiler flags: -C debuginfo=2 -C incremental --crate-type lib

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

error: Could not compile `bobbin-hz`.

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

[Centril]

cc @oli-obk

[oli-obk]

Minimal repro:

pub struct Hz;

impl Hz {
    pub const fn num(&self) -> u32 {
        42
    }
    pub const fn normalized(&self) -> Hz {
        Hz
    }

    pub const fn as_u32(&self) -> u32 {
        self.normalized().num()
    }
}

you need both the self, a method call .normalized, and a method call on the result of that in order to trigger promotion. It seems like self.normalized() is promoted to make a &Hz for the call to num

[oli-obk]

Ok, so promotion is indeed screwing up. The MIR is promoting the self argument.

4c4
< // disambiguator = before
---
> // disambiguator = after
14,24c14
<         StorageLive(_3);                 // bb0[1]: scope 0 at src/lib.rs:12:9: 12:26
<         StorageLive(_4);                 // bb0[2]: scope 0 at src/lib.rs:12:9: 12:13
<         _4 = &(*_1);                     // bb0[3]: scope 0 at src/lib.rs:12:9: 12:13
<         _3 = const Hz::normalized(move _4) -> [return: bb2, unwind: bb1]; // bb0[4]: scope 0 at src/lib.rs:12:9: 12:26
<                                          // ty::Const
<                                          // + ty: for<'r> fn(&'r Hz) -> Hz {Hz::normalized}
<                                          // + val: Scalar(Bits { size: 0, bits: 0 })
<                                          // mir::Constant
<                                          // + span: src/lib.rs:12:14: 12:24
<                                          // + ty: for<'r> fn(&'r Hz) -> Hz {Hz::normalized}
<                                          // + literal: Evaluated(Const { ty: for<'r> fn(&'r Hz) -> Hz {Hz::normalized}, val: Scalar(Bits { size: 0, bits: 0 }) })
---
>         goto -> bb2;                     // bb0[1]: scope 0 at src/lib.rs:12:9: 12:26
32,34c22,23
<         _2 = &_3;                        // bb2[0]: scope 0 at src/lib.rs:12:9: 12:26
<         StorageDead(_4);                 // bb2[1]: scope 0 at src/lib.rs:12:25: 12:26
<         _0 = const Hz::num(move _2) -> [return: bb3, unwind: bb1]; // bb2[2]: scope 0 at src/lib.rs:12:9: 12:32
---
>         _2 = &(promoted[0]: Hz);         // bb2[0]: scope 0 at src/lib.rs:12:9: 12:26
>         _0 = const Hz::num(move _2) -> [return: bb3, unwind: bb1]; // bb2[1]: scope 0 at src/lib.rs:12:9: 12:32
46,47c35
<         StorageDead(_3);                 // bb3[1]: scope 0 at src/lib.rs:13:5: 13:6
<         return;                          // bb3[2]: scope 0 at src/lib.rs:13:6: 13:6
---
>         return;                          // bb3[1]: scope 0 at src/lib.rs:13:6: 13:6

[pnkfelix]

triage: P-high. Looks under control.

[N5FPP]

Just to confirm, this has not made it out to the nightly, correct? As of today I am still seeing the same error when attempting to build bobbin-hz as part of bobbin-sdk.

[oli-obk]

No, #58784 is still open, I'll bump its priority