ice when running clippy-driver on ./ui/trivial-bounds/trivial-bounds-inconsistent.rs

[matthiaskrgr]

I'm reporting this in the rustc repo because this crash seems to happen in rustc code.
Feel free to move this to the clippy repo if its a clippy bug.

Code

This code is reduced from ./ui/trivial-bounds/trivial-bounds-inconsistent.rs

#![feature(trivial_bounds)]
fn use_for() where i32: Iterator { //~ WARNING trivial_bounds
    for _ in 2i32 {}
}
fn main() {}

Meta

rustc --version --verbose:

rustc 1.43.0-nightly (564758c4c 2020-03-08)
binary: rustc
commit-hash: 564758c4c329e89722454dd2fbb35f1ac0b8b47c
commit-date: 2020-03-08
host: x86_64-unknown-linux-gnu
release: 1.43.0-nightly
LLVM version: 9.0

clippy 0.0.212 (329923e 2020-03-04)

Error output

warning: function is never used: `use_for`
 --> ./ui/trivial-bounds/trivial-bounds-inconsistent.rs:2:4
  |
2 | fn use_for() where i32: Iterator { //~ WARNING trivial_bounds
  |    ^^^^^^^
  |
  = note: `#[warn(dead_code)]` on by default

error: internal compiler error: src/librustc_traits/normalize_erasing_regions.rs:35: could not fully normalize `std::option::Option<<i32 as std::iter::Iterator>::Item>`

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:875:9

Backtrace

warning: function is never used: `use_for`
 --> ./ui/trivial-bounds/trivial-bounds-inconsistent.rs:2:4
  |
2 | fn use_for() where i32: Iterator { //~ WARNING trivial_bounds
  |    ^^^^^^^
  |
  = note: `#[warn(dead_code)]` on by default

error: internal compiler error: src/librustc_traits/normalize_erasing_regions.rs:35: could not fully normalize `std::option::Option<<i32 as std::iter::Iterator>::Item>`

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:875:9
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.44/src/backtrace/libunwind.rs:86
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.44/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:1063
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1428
   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:204
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:224
  10: clippy_driver::report_clippy_ice
  11: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:474
  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_opt
  18: rustc::util::bug::opt_span_bug_fmt
  19: rustc::util::bug::bug_fmt
  20: rustc::ty::context::GlobalCtxt::enter_local
  21: rustc_traits::normalize_erasing_regions::normalize_ty_after_erasing_regions
  22: rustc::ty::query::__query_compute::normalize_ty_after_erasing_regions
  23: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::normalize_ty_after_erasing_regions>::compute
  24: rustc::dep_graph::graph::DepGraph::with_task_impl
  25: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  26: <rustc::ty::normalize_erasing_regions::NormalizeAfterErasingRegionsFolder as rustc::ty::fold::TypeFolder>::fold_ty
  27: rustc::ty::util::<impl rustc::ty::TyS>::needs_drop
  28: rustc_mir::dataflow::drop_flag_effects::on_all_children_bits::on_all_children_bits
  29: <rustc_mir::transform::elaborate_drops::ElaborateDrops as rustc_mir::transform::MirPass>::run_pass
  30: rustc_mir::transform::run_passes
  31: rustc_mir::transform::run_optimization_passes
  32: rustc_mir::transform::optimized_mir
  33: rustc::ty::query::__query_compute::optimized_mir
  34: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::optimized_mir>::compute
  35: rustc::dep_graph::graph::DepGraph::with_task_impl
  36: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  37: <clippy_lints::implicit_return::ImplicitReturn as rustc_lint::passes::LateLintPass>::check_fn
  38: <rustc_lint::late::LateLintPassObjects as rustc_lint::passes::LateLintPass>::check_fn
  39: rustc_hir::intravisit::walk_item
  40: rustc_hir::intravisit::Visitor::visit_nested_item
  41: rustc_hir::intravisit::walk_crate
  42: rustc_lint::late::late_lint_pass_crate
  43: rustc_session::utils::<impl rustc_session::session::Session>::time
  44: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:86
  45: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
  46: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:86
  47: rustc_session::utils::<impl rustc_session::session::Session>::time
  48: rustc_interface::passes::analysis
  49: rustc::ty::query::__query_compute::analysis
  50: rustc::dep_graph::graph::DepGraph::with_task_impl
  51: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  52: rustc::ty::context::tls::enter_global
  53: rustc_interface::interface::run_compiler_in_existing_thread_pool
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-clippy/issues/new

note: Clippy version: clippy 0.0.212 (329923e 2020-03-04)

query stack during panic:
#0 [normalize_ty_after_erasing_regions] normalizing `ParamEnvAnd { param_env: ParamEnv { caller_bounds: [], reveal: All, def_id: None }, value: std::option::Option<<i32 as std::iter::Iterator>::Item> }`
#1 [optimized_mir] processing `use_for`
#2 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to previous error

[sinkuu]

This is indeed an clippy bug. Under trivial_bounds functions may have unsatisfiable predicates, which prohibits instantiating them. implicit_return unconditionally tries to build MIRs for functions, but it should not.