use std::mem::MaybeUninit;
const N: usize = 2;
trait CollectArray<A>: Iterator<Item=A> {
fn inner_array(&mut self) -> [A; N];
fn collect_array(&mut self) -> [A; N] {
let result = self.inner_array();
assert!(self.next().is_none());
result
}
}
impl<A, I: ?Sized> CollectArray<A> for I where I: Iterator<Item=A> {
fn inner_array(&mut self) -> [A; N] {
let mut result: [MaybeUninit<A>; N] = unsafe {
MaybeUninit::uninit().assume_init()
};
for (dest, item) in result.iter_mut().zip(self) {
*dest = MaybeUninit::new(item);
}
let temp_ptr: *const [MaybeUninit<A>; N] = &result;
unsafe { std::ptr::read(temp_ptr as *const [A; N]) }
}
}
fn main() {
[[1, 2], [3, 4]]
.iter()
.map(|row| row.iter().collect_array())
.collect_array();
}Compiled with: rustc -Z mir-opt-level=2
Gives:
error: internal compiler error: compiler\rustc_traits\src\normalize_erasing_regions.rs:37:32: could not fully normalize `<&mut I as std::iter::IntoIterator>::IntoIter`
thread 'rustc' panicked at 'Box<Any>', compiler\rustc_errors\src\lib.rs:945:9
stack backtrace:
0: std::panicking::begin_panic
1: rustc_errors::HandlerInner::bug
2: rustc_errors::Handler::bug
3: rustc_middle::util::bug::opt_span_bug_fmt::{{closure}}
4: rustc_middle::ty::context::tls::with_opt::{{closure}}
5: rustc_middle::ty::context::tls::with_opt
6: rustc_middle::util::bug::opt_span_bug_fmt
7: rustc_middle::util::bug::bug_fmt
8: rustc_infer::infer::InferCtxtBuilder::enter
9: rustc_traits::normalize_erasing_regions::normalize_generic_arg_after_erasing_regions
10: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
11: rustc_data_structures::stack::ensure_sufficient_stack
12: rustc_query_system::query::plumbing::get_query_impl
13: rustc_middle::ty::normalize_erasing_regions::<impl rustc_middle::ty::context::TyCtxt>::normalize_erasing_regions
14: <rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt> as rustc_target::abi::LayoutOf>::layout_of
15: rustc_mir::transform::inline::Inliner::run_pass
16: <rustc_mir::transform::inline::Inline as rustc_mir::transform::MirPass>::run_pass
17: rustc_mir::transform::run_passes
18: rustc_mir::transform::run_optimization_passes
19: rustc_mir::transform::optimized_mir
20: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
21: rustc_data_structures::stack::ensure_sufficient_stack
22: rustc_query_system::query::plumbing::get_query_impl
23: rustc_middle::ty::<impl rustc_middle::ty::context::TyCtxt>::instance_mir
24: rustc_mir::monomorphize::collector::collect_neighbours
25: rustc_mir::monomorphize::collector::collect_items_rec
26: rustc_mir::monomorphize::collector::collect_items_rec
27: rustc_mir::monomorphize::collector::collect_items_rec
28: rustc_session::utils::<impl rustc_session::session::Session>::time
29: rustc_mir::monomorphize::collector::collect_crate_mono_items
30: rustc_mir::monomorphize::partitioning::collect_and_partition_mono_items
31: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::collect_and_partition_mono_items>::compute
32: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
33: rustc_data_structures::stack::ensure_sufficient_stack
34: rustc_query_system::query::plumbing::get_query_impl
35: rustc_codegen_ssa::base::codegen_crate
36: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::CodegenBackend>::codegen_crate
37: rustc_interface::passes::QueryContext::enter
38: rustc_interface::queries::Queries::ongoing_codegen
39: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
40: rustc_span::with_source_map
41: rustc_interface::interface::create_compiler_and_run
42: scoped_tls::ScopedKey<T>::set
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/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md
note: rustc 1.49.0-nightly (beb5ae474 2020-10-04) running on x86_64-pc-windows-gnu
note: compiler flags: -Z mir-opt-level=2
query stack during panic:
#0 [normalize_generic_arg_after_erasing_regions] normalizing `<&mut I as std::iter::IntoIterator>::IntoIter`
#1 [optimized_mir] optimizing MIR for `<I as CollectArray<A>>::inner_array`
#2 [collect_and_partition_mono_items] collect_and_partition_mono_items
end of query stack
error: aborting due to previous error
Compiled with: rustc -Z mir-opt-level=2
Gives: