rustc crash for gist 7c50ae4cb0d4169c289cbdeea491a48b

   Compiling playground v0.0.1 (/playground)
error[E0308]: mismatched types
 --> src/lib.rs:3:20
  |
3 |         return Err("c".to_string());
  |                    ^^^^^^^^^^^^^^^ expected struct `failure::error::Error`, found struct `std::string::String`
  |
  = note: expected type `failure::error::Error`
             found type `std::string::String`

error[E0317]: if may be missing an else clause
 --> src/lib.rs:2:5
  |
2 | /     if "a" != "b" {
3 | |         return Err("c".to_string());
4 | |     }
  | |_____^ expected (), found enum `std::result::Result`
  |
  = note: expected type `()`
             found type `std::result::Result<(), failure::error::Error>`
  = note: `if` expressions without `else` evaluate to `()`
  = help: consider adding an `else` block that evaluates to the expected type

error: internal compiler error: src/librustc/ty/context.rs:551: node_type: no type for node `expr { } (hir_id=HirId { owner: DefIndex(12), local_id: 3 })`

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:931:9
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.40/src/backtrace/libunwind.rs:88
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.40/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print_fmt
             at src/libstd/sys_common/backtrace.rs:77
   3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
             at src/libstd/sys_common/backtrace.rs:61
   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:65
   7: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:50
   8: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:188
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:205
  10: rustc_driver::report_ice
  11: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:468
  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::ty::context::TypeckTables::node_type::{{closure}}
  22: rustc::ty::context::TypeckTables::expr_ty
  23: <rustc_typeck::check::generator_interior::InteriorVisitor as rustc::hir::intravisit::Visitor>::visit_expr
  24: rustc::hir::intravisit::walk_expr
  25: <rustc_typeck::check::generator_interior::InteriorVisitor as rustc::hir::intravisit::Visitor>::visit_expr
  26: <rustc_typeck::check::generator_interior::InteriorVisitor as rustc::hir::intravisit::Visitor>::visit_expr
  27: <rustc_typeck::check::generator_interior::InteriorVisitor as rustc::hir::intravisit::Visitor>::visit_expr
  28: <rustc_typeck::check::generator_interior::InteriorVisitor as rustc::hir::intravisit::Visitor>::visit_expr
  29: rustc_typeck::check::generator_interior::resolve_interior
  30: rustc_typeck::check::FnCtxt::resolve_generator_interiors
  31: rustc::ty::context::tls::with_context::{{closure}}
  32: rustc_typeck::check::typeck_tables_of
  33: rustc::ty::query::__query_compute::typeck_tables_of
  34: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::typeck_tables_of>::compute
  35: rustc::dep_graph::graph::DepGraph::with_task_impl
  36: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  37: rustc::ty::query::__query_compute::typeck_tables_of
  38: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::typeck_tables_of>::compute
  39: rustc::dep_graph::graph::DepGraph::with_task_impl
  40: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  41: rustc_typeck::collect::checked_type_of
  42: rustc_typeck::collect::type_of
  43: rustc::ty::query::__query_compute::type_of
  44: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::type_of>::compute
  45: rustc::dep_graph::graph::DepGraph::with_task_impl
  46: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  47: rustc::hir::intravisit::walk_expr
  48: rustc::hir::intravisit::Visitor::visit_fn
  49: rustc::hir::intravisit::walk_item
  50: <rustc_typeck::collect::CollectItemTypesVisitor as rustc::hir::intravisit::Visitor>::visit_item
  51: rustc::hir::map::Map::visit_item_likes_in_module
  52: rustc_typeck::collect::collect_mod_item_types
  53: rustc::ty::query::__query_compute::collect_mod_item_types
  54: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::collect_mod_item_types>::compute
  55: rustc::dep_graph::graph::DepGraph::with_task_impl
  56: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  57: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::ensure_query
  58: rustc_typeck::check_crate::{{closure}}::{{closure}}
  59: rustc::util::common::time
  60: rustc_typeck::check_crate
  61: rustc_interface::passes::analysis
  62: rustc::ty::query::__query_compute::analysis
  63: rustc::dep_graph::graph::DepGraph::with_task_impl
  64: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  65: rustc_interface::passes::BoxedGlobalCtxt::access::{{closure}}
  66: rustc_interface::passes::create_global_ctxt::{{closure}}
  67: rustc_interface::passes::BoxedGlobalCtxt::enter
  68: rustc_interface::interface::run_compiler_in_existing_thread_pool
  69: std::thread::local::LocalKey<T>::with
  70: scoped_tls::ScopedKey<T>::set
  71: 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-beta.1 (76b40532a 2019-11-05) 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 [typeck_tables_of] processing `f`
#1 [typeck_tables_of] processing `f::{{closure}}#0`
#2 [type_of] processing `f::{{closure}}#0`
#3 [collect_mod_item_types] collecting item types in top-level module
#4 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to 3 previous errors

Some errors have detailed explanations: E0308, E0317.
For more information about an error, try `rustc --explain E0308`.
error: could not compile `playground`.

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