[ICE] with const generics and specified constant

[leonardo-m]

Related to ER #71387

#![feature(const_generics)]
#![allow(incomplete_features)]

use std::mem::MaybeUninit;

trait CollectSlice<'a>: Iterator {
    fn inner_array<const N: usize>(&mut self) -> [Self::Item; N];

    fn collect_array<const N: usize>(&mut self) -> [Self::Item; N] {
        let result = self.inner_array();
        assert!(self.next().is_none());
        result
    }
}

impl<'a, I: ?Sized> CollectSlice<'a> for I where I: Iterator {
    fn inner_array<const N: usize>(&mut self) -> [Self::Item; N] {
        let mut result: [MaybeUninit<Self::Item>; N] = unsafe {
            MaybeUninit::uninit().assume_init()
        };

        let mut count = 0;
        for (dest, item) in result.iter_mut().zip(self) {
            *dest = MaybeUninit::new(item);
            count += 1;
        }

        assert_eq!(N, count);

        let temp_ptr: *const [MaybeUninit<Self::Item>; N] = &result;
        unsafe { std::ptr::read(temp_ptr as *const [Self::Item; N]) }
    }
}

fn main() {
    let foos = [0_u64; 9].iter().cloned();
    let _bar: [u64; 9] = foos.collect_array::<9_usize>();
}

Gives:

error: internal compiler error: unexpected const parent in type_of_def_id(): Expr(Expr { hir_id: HirId { owner: DefId(0:21 ~ bug[317d]::main[0]), local_id: 23 }, kind: MethodCall(PathSegment { ident: collect_array#0, hir_id: Some(HirId { owner: DefId(0:21 ~ bug[317d]::main[0]), local_id: 20 }), res: Some(Err), args: Some(GenericArgs { args: [Const(ConstArg { value: AnonConst { hir_id: HirId { owner: DefId(0:21 ~ bug[317d]::main[0]), local_id: 18 }, body: BodyId { hir_id: HirId { owner: DefId(0:21 ~ bug[317d]::main[0]), local_id: 19 } } }, span: ...\bug.rs:37:47: 37:54 })], bindings: [], parenthesized: false }), infer_args: false }, ...\bug.rs:37:31: 37:44, [Expr { hir_id: HirId { owner: DefId(0:21 ~ bug[317d]::main[0]), local_id: 22 }, kind: Path(Resolved(None, Path { span: ...\bug.rs:37:26: 37:30, res: Local(HirId { owner: DefId(0:21 ~ bug[317d]::main[0]), local_id: 1 }), segments: [PathSegment { ident: foos#0, hir_id: Some(HirId { owner: DefId(0:21 ~ bug[317d]::main[0]), local_id: 21 }), res: Some(Local(HirId { owner: DefId(0:21 ~ bug[317d]::main[0]), local_id: 1 })), args: None, infer_args: true }] })), attrs: ThinVec(None), span: ...\bug.rs:37:26: 37:30 }]), attrs: ThinVec(None), span: ...\bug.rs:37:26: 37:57 })

error: internal compiler error: Const::from_anon_const: couldn't lit_to_const
  --> ...\bug.rs:37:47
   |
37 |     let _bar: [u64; 9] = foos.collect_array::<9_usize>();
   |                                               ^^^^^^^

error: internal compiler error: `ErrorReported` without an error
  --> ...\bug.rs:37:47
   |
37 |     let _bar: [u64; 9] = foos.collect_array::<9_usize>();
   |                                               ^^^^^^^

error: internal compiler error: cat_expr Errd
  --> ...\bug.rs:35:11
   |
35 |   fn main() {
   |  ___________^
36 | |     let foos = [0_u64; 9].iter().cloned();
37 | |     let _bar: [u64; 9] = foos.collect_array::<9_usize>();
38 | | }
   | |_^

error: internal compiler error: cat_expr Errd
  --> ...\bug.rs:37:26
   |
37 |     let _bar: [u64; 9] = foos.collect_array::<9_usize>();
   |                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: internal compiler error: PromoteTemps: MIR had errors
  --> ...\bug.rs:35:1
   |
35 | / fn main() {
36 | |     let foos = [0_u64; 9].iter().cloned();
37 | |     let _bar: [u64; 9] = foos.collect_array::<9_usize>();
38 | | }
   | |_^

error: internal compiler error: broken MIR in DefId(0:21 ~ bug[317d]::main[0]) ("return type"): bad type [type error]
  --> ...\bug.rs:35:1
   |
35 | / fn main() {
36 | |     let foos = [0_u64; 9].iter().cloned();
37 | |     let _bar: [u64; 9] = foos.collect_array::<9_usize>();
38 | | }
   | |_^

error: internal compiler error: broken MIR in DefId(0:21 ~ bug[317d]::main[0]) (LocalDecl { mutability: Mut, local_info: Other, internal: false, is_block_tail: None, ty: [type error], user_ty: UserTypeProjections { contents: [] }, source_info: SourceInfo { span: ...\bug.rs:35:1: 38:2, scope: scope[0] } }): bad type [type error]
  --> ...\bug.rs:35:1
   |
35 | / fn main() {
36 | |     let foos = [0_u64; 9].iter().cloned();
37 | |     let _bar: [u64; 9] = foos.collect_array::<9_usize>();
38 | | }
   | |_^

error: internal compiler error: mir_const_qualif: MIR had errors
  --> ...\bug.rs:37:47
   |
37 |     let _bar: [u64; 9] = foos.collect_array::<9_usize>();
   |                                               ^^^^^^^

error: internal compiler error: PromoteTemps: MIR had errors
  --> ...\bug.rs:37:47
   |
37 |     let _bar: [u64; 9] = foos.collect_array::<9_usize>();
   |                                               ^^^^^^^

error: internal compiler error: broken MIR in DefId(0:24 ~ bug[317d]::main[0]::{{constant}}[2]) ("return type"): bad type [type error]
  --> ...\bug.rs:37:47
   |
37 |     let _bar: [u64; 9] = foos.collect_array::<9_usize>();
   |                                               ^^^^^^^

error: internal compiler error: broken MIR in DefId(0:24 ~ bug[317d]::main[0]::{{constant}}[2]) (LocalDecl { mutability: Mut, local_info: Other, internal: false, is_block_tail: None, ty: [type error], user_ty: UserTypeProjections { contents: [] }, source_info: SourceInfo { span: ...\bug.rs:37:47: 37:54, scope: scope[0] } }): bad type [type error]
  --> ...\bug.rs:37:47
   |
37 |     let _bar: [u64; 9] = foos.collect_array::<9_usize>();
   |                                               ^^^^^^^

thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', src\librustc_errors\lib.rs:366:17

note: rustc 1.45.0-nightly (7f65393b9 2020-05-01) running on x86_64-pc-windows-gnu

[lcnr]

Probably related to #70507 (comment)

cc @varkor