Description
Description
Expressions involving an adaptor function like skip can cause an internal
compiler error. If a line of code in a submodule uses an undeclared type
or module in an expression using an adaptor, the compiler panics at
\'Box<Any>\', librustc_errors/lib.rs:543:9.
Code in a submodule needs to specify a path relative to the crate root, which
means prefixing :: to a call like std::env::args().
Example
We will use the following two files to demonstrate the issue:
main.rs:
mod lib;
use lib::foo;
fn main() {
let _ = foo();
}lib.rs:
pub fn foo() -> Vec<String> {
std::env::args() // <- [ERROR E0433] This _should_ be `::std::env::args()`.
.skip(1) // <- Compiler does not panic if this line is commented.
.collect()
}Code in a submodule needs to specify a path relative to the crate root, which
means prefixing :: to a call like std::env::args(). If we use
::std::env::args() the program compiles and runs successfully.
As written however, the files above cause this internal compiler error:
error[E0433]: failed to resolve. Use of undeclared type or module `std`
--> src/args.rs:6:5
|
6 | std::env::args()
| ^^^ Use of undeclared type or module `std`
error: internal compiler error: librustc/ich/impls_ty.rs:906: ty::TypeVariants::hash_stable() - Unexpected variant TyInfer(?0).
thread 'rustc' panicked at 'Box<Any>', librustc_errors/lib.rs:543:9
This panic will occur for other adapters, like take(n). After commenting out
the skip(1) line, the compiler does not panic. and only this output is seen
after trying to compile:
error[E0433]: failed to resolve. Use of undeclared type or module `std`
--> src/lib.rs:5:5
|
5 | std::env::args()
| ^^^ Use of undeclared type or module `std`
error: aborting due to previous error
For more information about this error, try `rustc --explain E0433`.
Potential UX Fixes
I ran into this error because the :: error is not required for code in the
crate root. If foo is moved from lib.rc to main.rs, then the internal
compiler error no longer occurs.
If code outside of the crate root causes an error due to the use of an
undeclared type or module, it would be nice if the compiler warning would
mention the possibility of a missing :: prefix, if the name that could not
be resolved was a type or module in the standard library.
When I reviewed the information given by running rustc --explain E0433, it
mostly mentions the possibility of typos being the cause of this error.
Mentioning some other common situations that lead to symbols failing to
resolve might be helpful.
Meta
rustc --version --verbose:
rustc 1.26.0-nightly (5508b2714 2018-03-18)
binary: rustc
commit-hash: 5508b27145cfb82896ae838e6aca0cd48750796f
commit-date: 2018-03-18
host: x86_64-unknown-linux-gnu
release: 1.26.0-nightly
LLVM version: 6.0
Backtrace:
Compiling bug-report v0.1.0 (file:///home/user/Projects/rustc-bug)
error[E0433]: failed to resolve. Use of undeclared type or module `std`
--> src/args.rs:6:5
|
6 | std::env::args()
| ^^^ Use of undeclared type or module `std`
error: internal compiler error: librustc/ich/impls_ty.rs:906: ty::TypeVariants::hash_stable() - Unexpected variant TyInfer(?0).
thread 'rustc' panicked at 'Box<Any>', librustc_errors/lib.rs:543:9
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 libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
1: std::sys_common::backtrace::print
at libstd/sys_common/backtrace.rs:71
at libstd/sys_common/backtrace.rs:59
2: std::panicking::default_hook::{{closure}}
at libstd/panicking.rs:207
3: std::panicking::default_hook
at libstd/panicking.rs:223
4: core::ops::function::Fn::call
5: std::panicking::rust_panic_with_hook
at libstd/panicking.rs:403
6: std::panicking::begin_panic
7: rustc_errors::Handler::bug
8: rustc::session::opt_span_bug_fmt::{{closure}}
9: rustc::ty::context::tls::with_opt::{{closure}}
10: <std::thread::local::LocalKey<T>>::try_with
11: <std::thread::local::LocalKey<T>>::with
12: rustc::ty::context::tls::with
13: rustc::ty::context::tls::with_opt
14: rustc::session::opt_span_bug_fmt
15: rustc::session::bug_fmt
16: rustc::ich::impls_ty::<impl rustc_data_structures::stable_hasher::HashStable<rustc::ich::hcx::StableHashingContext<'a>> for rustc::ty::sty::TypeVariants<'gcx>>::hash_stable
17: <T as rustc::dep_graph::dep_node::DepNodeParams<'a, 'gcx, 'tcx>>::to_fingerprint
18: rustc::dep_graph::dep_node::DepNode::new
19: rustc::ty::maps::<impl rustc::ty::maps::queries::dropck_outlives<'tcx>>::try_get
20: rustc::ty::maps::TyCtxtAt::dropck_outlives
21: rustc::traits::query::dropck_outlives::<impl rustc::infer::at::At<'cx, 'gcx, 'tcx>>::dropck_outlives
22: rustc_typeck::check::dropck::check_safety_of_destructor_if_necessary
23: rustc_typeck::check::regionck::RegionCtxt::check_safety_of_rvalue_destructor_if_necessary
24: <rustc_typeck::check::regionck::RegionCtxt<'a, 'gcx, 'tcx> as rustc::hir::intravisit::Visitor<'gcx>>::visit_expr
25: rustc::hir::intravisit::walk_expr
26: <rustc_typeck::check::regionck::RegionCtxt<'a, 'gcx, 'tcx> as rustc::hir::intravisit::Visitor<'gcx>>::visit_expr
27: rustc::hir::intravisit::walk_expr
28: <rustc_typeck::check::regionck::RegionCtxt<'a, 'gcx, 'tcx> as rustc::hir::intravisit::Visitor<'gcx>>::visit_expr
29: <rustc_typeck::check::regionck::RegionCtxt<'a, 'gcx, 'tcx> as rustc::hir::intravisit::Visitor<'gcx>>::visit_expr
30: rustc_typeck::check::regionck::RegionCtxt::visit_fn_body
31: rustc_typeck::check::regionck::<impl rustc_typeck::check::FnCtxt<'a, 'gcx, 'tcx>>::regionck_fn
32: rustc::ty::context::tls::enter
33: rustc::infer::InferCtxtBuilder::enter
34: rustc_typeck::check::typeck_tables_of
35: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_tables_of<'tcx>>::compute_result
36: rustc::dep_graph::graph::DepGraph::with_task_impl
37: rustc_errors::Handler::track_diagnostics
38: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::cycle_check
39: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_tables_of<'tcx>>::force
40: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_tables_of<'tcx>>::try_get
41: rustc::ty::maps::TyCtxtAt::typeck_tables_of
42: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_tables_of<'tcx>>::ensure
43: rustc::session::Session::track_errors
44: rustc_typeck::check::typeck_item_bodies
45: rustc::dep_graph::graph::DepGraph::with_task_impl
46: rustc_errors::Handler::track_diagnostics
47: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::cycle_check
48: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_item_bodies<'tcx>>::force
49: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_item_bodies<'tcx>>::try_get
50: rustc::ty::maps::TyCtxtAt::typeck_item_bodies
51: rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::typeck_item_bodies
52: rustc_typeck::check_crate
53: <std::thread::local::LocalKey<T>>::with
54: <std::thread::local::LocalKey<T>>::with
55: rustc::ty::context::TyCtxt::create_and_enter
56: rustc_driver::driver::compile_input
57: rustc_driver::run_compiler_impl
58: syntax::with_globals
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 1.26.0-nightly (5508b2714 2018-03-18) running on x86_64-unknown-linux-gnu
note: compiler flags: -C debuginfo=2 -C incremental --crate-type bin
note: some of the compiler flags provided by cargo are hidden
error: Could not compile `bug-report`.
To learn more, run the command again with --verbose.
P.S. I am still somewhat new to Rust, but I would love to help out with this however I can!