ICE: src/librustc_lint/types.rs:858: unexpected type in foreign function: T

[Centril]

fn _f<T>() {
    extern "C" {
        static _a: *const T;
    }
}

backtrace:

   Compiling playground v0.0.1 (/playground)
error: internal compiler error: src/librustc_lint/types.rs:858: unexpected type in foreign function: T

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:912:9
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.37/src/backtrace/libunwind.rs:88
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.37/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print_fmt
             at src/libstd/sys_common/backtrace.rs:76
   3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
             at src/libstd/sys_common/backtrace.rs:60
   4: core::fmt::write
             at src/libcore/fmt/mod.rs:1028
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1412
   6: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:64
   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:196
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:210
  10: rustc_driver::report_ice
  11: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:477
  12: std::panicking::begin_panic
  13: rustc_errors::HandlerInner::bug
  14: rustc_errors::Handler::bug
  15: rustc::util::bug::opt_span_bug_fmt::{{closure}}
  16: rustc::ty::context::tls::with_opt::{{closure}}
  17: rustc::ty::context::tls::with_context_opt
  18: rustc::ty::context::tls::with_opt
  19: rustc::util::bug::opt_span_bug_fmt
  20: rustc::util::bug::bug_fmt
  21: rustc_lint::types::ImproperCTypesVisitor::check_type_for_ffi
  22: rustc_lint::types::ImproperCTypesVisitor::check_type_for_ffi
  23: rustc_lint::types::ImproperCTypesVisitor::check_type_for_ffi_and_report_errors
  24: <rustc_lint::types::ImproperCTypes as rustc::lint::LateLintPass>::check_foreign_item
  25: rustc::hir::intravisit::walk_item
  26: rustc::hir::intravisit::Visitor::visit_nested_item
  27: rustc::hir::intravisit::walk_block
  28: rustc::hir::intravisit::walk_body
  29: rustc::hir::intravisit::walk_fn
  30: rustc::hir::intravisit::walk_item
  31: rustc::hir::intravisit::Visitor::visit_nested_item
  32: rustc::lint::context::late_lint_mod
  33: rustc::ty::query::__query_compute::lint_mod
  34: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::lint_mod>::compute
  35: rustc::dep_graph::graph::DepGraph::with_task_impl
  36: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  37: rustc::lint::context::check_crate::{{closure}}::{{closure}}
  38: rustc::util::common::time
  39: rustc::util::common::time
  40: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:80
  41: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
  42: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:80
  43: rustc_interface::passes::analysis::{{closure}}
  44: rustc::util::common::time
  45: rustc_interface::passes::analysis
  46: rustc::ty::query::__query_compute::analysis
  47: rustc::dep_graph::graph::DepGraph::with_task_impl
  48: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  49: rustc_interface::passes::BoxedGlobalCtxt::access::{{closure}}
  50: rustc_interface::passes::create_global_ctxt::{{closure}}
  51: rustc_interface::interface::run_compiler_in_existing_thread_pool
  52: std::thread::local::LocalKey<T>::with
  53: scoped_tls::ScopedKey<T>::set
  54: syntax::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 1.40.0-nightly (702b45e40 2019-10-01) 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

query stack during panic:
#0 [lint_mod] linting top-level module
#1 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to previous error

error: could not compile `playground`.

[Centril]

Related to #65025.

[pnkfelix]

triage: P-medium, removing nomination label.

[Centril]

Curiously, this seems specific to statics... fn items correctly error:

fn _f<T>() {
    extern "C" {
        fn foo(_a: *const T);
    }
}