Rust: ICE with incorrect turbofish

[cramertj]

struct A{}
struct B{}

impl From<A> for B {
    fn from(a: A) -> B {
        B{}
    }
}

fn main() {
    let c1 = A{};
    let c2: B = c1::<Into<B>>.into();
    let _ = c2;
}

gives

error: internal compiler error: src/librustc_typeck/check/mod.rs:2456: no type for node 48: type B (hir_id=HirId { owner: DefIndex(16), local_id: 13 }) in fcx 0x7f3fb3fec990

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:637:9
note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
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 1.36.0-nightly (6afcb5628 2019-05-19) running on x86_64-unknown-linux-gnu

note: compiler flags: -C codegen-units=1 -C debuginfo=2 --crate-type bin

[estebank]

Prior output:

error[E0109]: type arguments are not allowed on this entity
  --> <source>:12:22
   |
12 |     let c2: B = c1::<Into<B>>.into();
   |                      ^^^^^^^ type argument not allowed

[Centril]

Possibly related to const generics? cc @varkor

With backtrace:

error: internal compiler error: src/librustc_typeck/check/mod.rs:2456: no type for node 48: type B (hir_id=HirId { owner: DefIndex(16), local_id: 13 }) in fcx 0x7f82da7ec990

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:637:9
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 src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:39
   1: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:71
   2: std::panicking::default_hook::{{closure}}
             at src/libstd/sys_common/backtrace.rs:59
             at src/libstd/panicking.rs:197
   3: std::panicking::default_hook
             at src/libstd/panicking.rs:211
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:478
   6: std::panicking::begin_panic
   7: rustc_errors::Handler::bug
   8: rustc::util::bug::opt_span_bug_fmt::{{closure}}
   9: rustc::ty::context::tls::with_opt::{{closure}}
  10: rustc::ty::context::tls::with_context_opt
  11: rustc::ty::context::tls::with_opt
  12: rustc::util::bug::opt_span_bug_fmt
  13: rustc::util::bug::bug_fmt
  14: rustc_typeck::check::FnCtxt::node_ty
  15: <rustc_typeck::check::writeback::WritebackCx as rustc::hir::intravisit::Visitor>::visit_ty
  16: rustc::hir::intravisit::walk_path
  17: rustc::hir::intravisit::walk_ty
  18: <rustc_typeck::check::writeback::WritebackCx as rustc::hir::intravisit::Visitor>::visit_ty
  19: rustc::hir::intravisit::walk_path
  20: <rustc_typeck::check::writeback::WritebackCx as rustc::hir::intravisit::Visitor>::visit_expr
  21: rustc::hir::intravisit::walk_expr
  22: <rustc_typeck::check::writeback::WritebackCx as rustc::hir::intravisit::Visitor>::visit_expr
  23: <rustc_typeck::check::writeback::WritebackCx as rustc::hir::intravisit::Visitor>::visit_local
  24: rustc::hir::intravisit::walk_expr
  25: <rustc_typeck::check::writeback::WritebackCx as rustc::hir::intravisit::Visitor>::visit_expr
  26: rustc_typeck::check::writeback::<impl rustc_typeck::check::FnCtxt>::resolve_type_vars_in_body
  27: rustc::ty::context::GlobalCtxt::enter_local
  28: rustc_typeck::check::typeck_tables_of
  29: rustc::ty::query::__query_compute::typeck_tables_of
  30: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::typeck_tables_of>::compute
  31: rustc::dep_graph::graph::DepGraph::with_task_impl
  32: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  33: rustc::ty::<impl rustc::ty::context::TyCtxt>::par_body_owners
  34: rustc_typeck::check::typeck_item_bodies
  35: rustc::ty::query::__query_compute::typeck_item_bodies
  36: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::typeck_item_bodies>::compute
  37: rustc::dep_graph::graph::DepGraph::with_task_impl
  38: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  39: rustc::util::common::time
  40: rustc_typeck::check_crate
  41: rustc_interface::passes::analysis
  42: rustc::ty::query::__query_compute::analysis
  43: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::analysis>::compute
  44: rustc::dep_graph::graph::DepGraph::with_task_impl
  45: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  46: rustc::ty::context::tls::enter_global
  47: rustc_interface::passes::BoxedGlobalCtxt::access::{{closure}}
  48: rustc_interface::passes::create_global_ctxt::{{closure}}
  49: rustc_interface::interface::run_compiler_in_existing_thread_pool
  50: std::thread::local::LocalKey<T>::with
  51: scoped_tls::ScopedKey<T>::set
  52: syntax::with_globals
query stack during panic:
#0 [typeck_tables_of] processing `main`
#1 [typeck_item_bodies] type-checking all item bodies
#2 [analysis] running analysis passes on this crate
end of query stack
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 1.36.0-nightly (6afcb5628 2019-05-19) running on x86_64-unknown-linux-gnu

note: compiler flags: -C codegen-units=1 -C debuginfo=2 --crate-type bin

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

error: Could not compile `playground`.

[hellow554]

Regression in 2c8bbf50db0ef90a33f986ba8fc2e1fe129197ff

[pietroalbini]

cc @rust-lang/release

[pnkfelix]

triage: P-high. Leaving I-nominated to discuss at triage meeting in terms of how quickly we might address this.

[pietroalbini]

Manually bisected (by building rustc a few times) locally, the cause is https://github.com/rust-lang/rust/pull/59025.
cc @varkor @rust-lang/compiler

[pnkfelix]

triage: discussed at compiler team meeting. We're seeing what we come up with in short term. Removing nomination tag.

[Centril]

Slight reduction:

struct A {}
struct B {}

impl From<A> for B {}

fn main() {
    let c1 = A {};
    c1::<Into<B>>;
}

[Centril]

Maximal reduction:

fn main() {
    let c1 = ();
    c1::<()>;
}

[estebank]

The stable backport #61085 will land soon, will still need to be addressed in master _and_ beta.

[pietroalbini]

As I wrote in https://github.com/rust-lang/rust/pull/61085#issuecomment-495358876 this didn't make in 1.35.0. Someone needs to forward-port the change to master and beta-nominate it.

[oli-obk]

I'll create the appropriate PRs over the weekend

[czipperz]

Is there a test case that makes sure this minimal example compiles? This seems like a good regression test to add. @Centril

[oli-obk]

There is one in the fix PR: https://github.com/rust-lang/rust/pull/61189/files#diff-94ce7caf137efdc57471092222a49b4c that covers both cases of the examples in this issue

[czipperz]

I guess I missed it when scrolling through the diff

[czipperz]

How the heck did this pass through tests? Was turbo fish completely untested? Or is this behavior specific to when it is a value and not a function call being turbo fished?

[Centril]

@czipperz Our conclusion from the compiler team meeting is that we simply are to reactive with testing and that we don't generally have sufficient test coverage. Let's try to change that moving forward.

[jonas-schievink]

@czipperz The ICE doesn't occur on all uses of the turbofish. If you look at the example provided here, it shouldn't actually have compiled. Getting an ICE instead of a compiler error is still bad, of course, but not nearly as bad as having all uses of the turbofish syntax result in an ICE.

[czipperz]

@Centril Thanks. Is there a code coverage tool that supports utilities like line coverage?

@jonas-schievink Yeah it's really hard to test every invalid case is handled correctly.

[czipperz]

Does someone want to maybe set up kcov to run with continuous integration?

[oli-obk]

Is there a code coverage tool that supports utilities like line coverage?

Some are linked in https://github.com/rust-lang/rfcs/issues/646#issuecomment-427644574

Does someone want to maybe set up kcov to run with continuous integration?

That's an independent topic to this issue, if you want you can open a separate issue for it, but we should keep this issue targeted to the ICE at hand.

[estebank]

ICE no longer reproduces.

[varkor]

This issue already has a test (https://github.com/rust-lang/rust/blob/master/src/test/ui/issues/issue-60989.rs), so I think it can just be closed.