`extern crate self as core` in libcore is an ICE

[jyn514]

I tried this code:

// Allow using [`core::u16`], etc. in intra-doc links.
#[allow(unused_extern_crates)]
extern crate self as core;

I expected to see this happen: Either the crate compiles successfully or gives a reasonable error.

Instead, this happened:

$ x.py check
    Checking core v0.0.0 (/home/joshua/src/rust/src/libcore)
error: internal compiler error: src/librustc_middle/hir/map/mod.rs:499: couldn't find hir id HirId { owner: DefId(0:0 ~ core[3620]), local_id: 0 } in the HIR map

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:907:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Found while working on #73445.

Meta

build/x86_64-unknown-linux-gnu/stage0/bin/rustc --version -v:

rustc 1.45.0-beta.3359 (b7dc83a3f 2020-06-03)
binary: rustc
commit-hash: b7dc83a3f6ca9746fb3d121761c3605477b77d90
commit-date: 2020-06-03
host: x86_64-unknown-linux-gnu
release: 1.45.0-beta.3359
LLVM version: 10.0

Backtrace

error: internal compiler error: src/librustc_middle/hir/map/mod.rs:499: couldn't find hir id HirId { owner: DefId(0:0 ~ core[3620]), local_id: 0 } in the HIR map

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:907:9
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:218
  10: rustc_driver::report_ice
  11: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:490
  12: std::panicking::begin_panic
  13: rustc_errors::HandlerInner::bug
  14: rustc_errors::Handler::bug
  15: rustc_middle::util::bug::opt_span_bug_fmt::{{closure}}
  16: rustc_middle::ty::context::tls::with_opt::{{closure}}
  17: rustc_middle::ty::context::tls::with_opt
  18: rustc_middle::util::bug::opt_span_bug_fmt
  19: rustc_middle::util::bug::bug_fmt
  20: rustc_middle::hir::map::Map::get::{{closure}}
  21: rustc_middle::hir::map::Map::get
  22: rustc_privacy::def_id_visibility
  23: rustc_privacy::EmbargoVisitor::update_macro_reachable
  24: <rustc_privacy::EmbargoVisitor as rustc_hir::intravisit::Visitor>::visit_macro_def
  25: rustc_privacy::privacy_access_levels
  26: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::privacy_access_levels>::compute
  27: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  28: rustc_data_structures::stack::ensure_sufficient_stack
  29: rustc_query_system::query::plumbing::get_query_impl
  30: rustc_query_system::query::plumbing::ensure_query_impl
  31: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
  32: rustc_session::utils::<impl rustc_session::session::Session>::time
  33: rustc_interface::passes::analysis
  34: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::analysis>::compute
  35: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  36: rustc_query_system::query::plumbing::get_query_impl
  37: rustc_middle::ty::context::tls::enter_global
  38: rustc_interface::interface::run_compiler_in_existing_thread_pool
  39: rustc_ast::attr::with_globals
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

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 1.45.0-beta.3359 (b7dc83a3f 2020-06-03) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z macro-backtrace -Z binary-dep-depinfo -Z force-unstable-if-unmarked -C opt-level=3 -C embed-bitcode=no -C codegen-units=8 -C debuginfo=1 -C link-args=-Wl,-rpath,$ORIGIN/../lib -C prefer-dynamic -C debug-assertions=y --crate-type lib

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

query stack during panic:
#0 [privacy_access_levels] privacy access levels
#1 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to previous error

[jyn514]

@rustbot modify labels: I-ICE

[jyn514]

This now works!