ICE: Failed to get layout for `[type error]`:

[DutchGhost]

I hit this ice when trying implement #60735.
The ice message looks very similar to #70291, which has been closed already.

Code

#![feature(const_generics)]

trait ConstChunksExactTrait<T> {
    fn const_chunks_exact<const N: usize>(&self) -> ConstChunksExact<'_, T, {N}>;
}

impl <T> ConstChunksExactTrait<T> for [T] {
    fn const_chunks_exact<const N: usize>(&self) -> ConstChunksExact<'_, T, {N}> {

        assert!(N != 0);
        let rem = self.len() % N;
        let len = self.len() - rem;
        let (fst, snd) = self.split_at(len);
        ConstChunksExact { v: fst, rem: snd }
    }
}

struct ConstChunksExact<'a, T: 'a, const N: usize> {
    v: &'a [T],
    rem: &'a [T]
}

impl <'a, T, const N: usize> Iterator for ConstChunksExact<'a, T, {N}> {
    type Item = [&'a T; N];
    
    fn next(&mut self) -> Option<Self::Item> {
        if self.v.len() < N {
            None
        } else {
            let (fst, snd) = self.v.split_at(N);
            
            self.v = snd;
            
            let ptr = fst.as_ptr() as *const _;
            Some(unsafe { *ptr})
        }
    }
}

fn main() {
    let slice = &[1i32, 2, 3, 4, 5, 6, 7, 8, 9, 10];
    
    for a in slice.const_chunks_exact::<{3usize}>() {
        dbg!(a);
    }
}

Meta

rustc --version --verbose:

rustc 1.44.0-nightly (75208942f 2020-03-27)

Backtrace

error: internal compiler error: src/librustc_codegen_llvm/context.rs:854: failed to get layout for `[type error]`: the type `[type error]` has an unknown layout

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:880:9
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/libunwind.rs:86
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.46/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:1069
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1439
   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:198
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:218
  10: rustc_driver::report_ice
  11: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:515
  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_codegen_llvm::context::CodegenCx as rustc_target::abi::LayoutOf>::spanned_layout_of::{{closure}}
  21: <rustc_codegen_llvm::context::CodegenCx as rustc_target::abi::LayoutOf>::spanned_layout_of
  22: rustc_codegen_ssa::mir::analyze::non_ssa_locals
  23: rustc_codegen_ssa::mir::codegen_mir
  24: <rustc::mir::mono::MonoItem as rustc_codegen_ssa::mono_item::MonoItemExt>::define
  25: rustc_codegen_llvm::base::compile_codegen_unit::module_codegen
  26: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task
  27: rustc_codegen_llvm::base::compile_codegen_unit
  28: rustc_codegen_ssa::base::codegen_crate
  29: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::CodegenBackend>::codegen_crate
  30: rustc_interface::passes::start_codegen
  31: rustc::ty::context::tls::enter_global
  32: rustc_interface::queries::Queries::ongoing_codegen
  33: rustc_interface::interface::run_compiler_in_existing_thread_pool
  34: rustc_ast::attr::with_globals
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/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.44.0-nightly (75208942f 2020-03-27) 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

query stack during panic:
end of query stack
error: aborting due to previous error

error: could not compile `playground`.

[steffahn]

When I switch from “Run” to “Build” in the playground, the error changes.

Long error message (collapsed)

   Compiling playground v0.0.1 (/playground)
warning: the feature `const_generics` is incomplete and may cause the compiler to crash
 --> src/lib.rs:1:12
  |
1 | #![feature(const_generics)]
  |            ^^^^^^^^^^^^^^
  |
  = note: `#[warn(incomplete_features)]` on by default

warning: field is never read: `rem`
  --> src/lib.rs:20:5
   |
20 |     rem: &'a [T]
   |     ^^^^^^^^^^^^
   |
   = note: `#[warn(dead_code)]` on by default

warning: function is never used: `main`
  --> src/lib.rs:40:4
   |
40 | fn main() {
   |    ^^^^

error: internal compiler error: unexpected const parent in type_of_def_id(): Expr(Expr { hir_id: HirId { owner: DefId(0:27 ~ playground[7ff2]::main[0]), local_id: 30 }, kind: MethodCall(PathSegment { ident: const_chunks_exact#0, hir_id: Some(HirId { owner: DefId(0:27 ~ playground[7ff2]::main[0]), local_id: 27 }), res: Some(Err), args: Some(GenericArgs { args: [Const(ConstArg { value: AnonConst { hir_id: HirId { owner: DefId(0:27 ~ playground[7ff2]::main[0]), local_id: 23 }, body: BodyId { hir_id: HirId { owner: DefId(0:27 ~ playground[7ff2]::main[0]), local_id: 26 } } }, span: src/lib.rs:43:41: 43:49 })], bindings: [], parenthesized: false }), infer_args: false }, src/lib.rs:43:20: 43:38, [Expr { hir_id: HirId { owner: DefId(0:27 ~ playground[7ff2]::main[0]), local_id: 29 }, kind: Path(Resolved(None, Path { span: src/lib.rs:43:14: 43:19, res: Local(HirId { owner: DefId(0:27 ~ playground[7ff2]::main[0]), local_id: 1 }), segments: [PathSegment { ident: slice#0, hir_id: Some(HirId { owner: DefId(0:27 ~ playground[7ff2]::main[0]), local_id: 28 }), res: Some(Local(HirId { owner: DefId(0:27 ~ playground[7ff2]::main[0]), local_id: 1 })), args: None, infer_args: true }] })), attrs: ThinVec(None), span: src/lib.rs:43:14: 43:19 }]), attrs: ThinVec(None), span: src/lib.rs:43:14: 43:52 })

error: internal compiler error: cat_expr Errd
  --> src/lib.rs:43:41
   |
43 |     for a in slice.const_chunks_exact::<{3usize}>() {
   |                                         ^^^^^^^^

error: internal compiler error: cat_expr Errd
  --> src/lib.rs:40:11
   |
40 |   fn main() {
   |  ___________^
41 | |     let slice = &[1i32, 2, 3, 4, 5, 6, 7, 8, 9, 10];
42 | |     
43 | |     for a in slice.const_chunks_exact::<{3usize}>() {
44 | |         dbg!(a);
45 | |     }
46 | | }
   | |_^

error: internal compiler error: cat_expr Errd
  --> src/lib.rs:43:14
   |
43 |     for a in slice.const_chunks_exact::<{3usize}>() {
   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: internal compiler error: cat_expr Errd
  --> src/lib.rs:43:9
   |
43 |     for a in slice.const_chunks_exact::<{3usize}>() {
   |         ^

error: internal compiler error: cat_expr Errd
  --> src/lib.rs:44:9
   |
44 |         dbg!(a);
   |         ^^^^^^^^
   |
   = note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

error: internal compiler error: cat_expr Errd
  --> src/lib.rs:44:14
   |
44 |         dbg!(a);
   |              ^

error: internal compiler error: cat_expr Errd
  --> src/lib.rs:44:9
   |
44 |         dbg!(a);
   |         ^^^^^^^^
   |
   = note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

error: internal compiler error: cat_expr Errd
  --> src/lib.rs:44:9
   |
44 |         dbg!(a);
   |         ^^^^^^^^
   |
   = note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

error: internal compiler error: cat_expr Errd
  --> src/lib.rs:44:9
   |
44 |         dbg!(a);
   |         ^^^^^^^^
   |
   = note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

error: internal compiler error: cat_expr Errd
  --> src/lib.rs:44:9
   |
44 |         dbg!(a);
   |         ^^^^^^^^
   |
   = note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

error: internal compiler error: cat_expr Errd
  --> src/lib.rs:44:9
   |
44 |         dbg!(a);
   |         ^^^^^^^^
   |
   = note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

error: internal compiler error: cat_expr Errd
  --> src/lib.rs:44:9
   |
44 |         dbg!(a);
   |         ^^^^^^^^
   |
   = note: this error: internal compiler error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

error: internal compiler error: PromoteTemps: MIR had errors
  --> src/lib.rs:40:1
   |
40 | / fn main() {
41 | |     let slice = &[1i32, 2, 3, 4, 5, 6, 7, 8, 9, 10];
42 | |     
43 | |     for a in slice.const_chunks_exact::<{3usize}>() {
44 | |         dbg!(a);
45 | |     }
46 | | }
   | |_^

error: internal compiler error: broken MIR in DefId(0:27 ~ playground[7ff2]::main[0]) ("return type"): bad type [type error]
  --> src/lib.rs:40:1
   |
40 | / fn main() {
41 | |     let slice = &[1i32, 2, 3, 4, 5, 6, 7, 8, 9, 10];
42 | |     
43 | |     for a in slice.const_chunks_exact::<{3usize}>() {
44 | |         dbg!(a);
45 | |     }
46 | | }
   | |_^

error: internal compiler error: broken MIR in DefId(0:27 ~ playground[7ff2]::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: src/lib.rs:40:1: 46:2, scope: scope[0] } }): bad type [type error]
  --> src/lib.rs:40:1
   |
40 | / fn main() {
41 | |     let slice = &[1i32, 2, 3, 4, 5, 6, 7, 8, 9, 10];
42 | |     
43 | |     for a in slice.const_chunks_exact::<{3usize}>() {
44 | |         dbg!(a);
45 | |     }
46 | | }
   | |_^

error: internal compiler error: mir_const_qualif: MIR had errors
  --> src/lib.rs:43:41
   |
43 |     for a in slice.const_chunks_exact::<{3usize}>() {
   |                                         ^^^^^^^^

error: internal compiler error: PromoteTemps: MIR had errors
  --> src/lib.rs:43:41
   |
43 |     for a in slice.const_chunks_exact::<{3usize}>() {
   |                                         ^^^^^^^^

error: internal compiler error: broken MIR in DefId(0:28 ~ playground[7ff2]::main[0]::{{constant}}[0]) ("return type"): bad type [type error]
  --> src/lib.rs:43:41
   |
43 |     for a in slice.const_chunks_exact::<{3usize}>() {
   |                                         ^^^^^^^^

error: internal compiler error: broken MIR in DefId(0:28 ~ playground[7ff2]::main[0]::{{constant}}[0]) (LocalDecl { mutability: Mut, local_info: Other, internal: false, is_block_tail: None, ty: [type error], user_ty: UserTypeProjections { contents: [] }, source_info: SourceInfo { span: src/lib.rs:43:41: 43:49, scope: scope[0] } }): bad type [type error]
  --> src/lib.rs:43:41
   |
43 |     for a in slice.const_chunks_exact::<{3usize}>() {
   |                                         ^^^^^^^^

thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', src/librustc_errors/lib.rs:360:17
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

error: internal compiler error: unexpected panic

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 1.44.0-nightly (75208942f 2020-03-27) running on x86_64-unknown-linux-gnu

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

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

error: could not compile `playground`.

To learn more, run the command again with --verbose.

When I change the call

slice.const_chunks_exact::<{3usize}>()

into

<[i32] as ConstChunksExactTrait<i32>>::const_chunks_exact::<{3usize}>(slice)

the ICE disappears. (The code segfaults though.)

Bisection gives:
searched nightlies: from nightly-2020-03-24 to nightly-2020-03-26
regressed nightly: nightly-2020-03-25
searched commits: from 1edd389 to 02046a5
regressed commit: 342c5f3

[DutchGhost]

On that segfault, thats my own mistake, the Iterator should yield items of type &'a [T; N], rather than [&'a T; N] and the return expression should be Some(unsafe { &*ptr})

[steffahn]

Yeah, that’s what I thought, the segfault being a bug in the unsafe code.

Here’s a smaller example:

#![feature(const_generics)]

struct R;
impl R {
    fn method<const N: u8>(&self) {}
}
fn main() {
    R.method::<1u8>();
}

(Playground)

Errors:

   Compiling playground v0.0.1 (/playground)
warning: the feature `const_generics` is incomplete and may cause the compiler to crash
 --> src/main.rs:1:12
  |
1 | #![feature(const_generics)]
  |            ^^^^^^^^^^^^^^
  |
  = note: `#[warn(incomplete_features)]` on by default

error: internal compiler error: src/librustc_codegen_llvm/context.rs:854: failed to get layout for `[type error]`: the type `[type error]` has an unknown layout

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:880:9
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/libunwind.rs:86
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.46/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:1069
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1439
   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:198
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:218
  10: rustc_driver::report_ice
  11: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:515
  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_codegen_llvm::context::CodegenCx as rustc_target::abi::LayoutOf>::spanned_layout_of::{{closure}}
  21: <rustc_codegen_llvm::context::CodegenCx as rustc_target::abi::LayoutOf>::spanned_layout_of
  22: rustc_codegen_ssa::mir::analyze::non_ssa_locals
  23: rustc_codegen_ssa::mir::codegen_mir
  24: <rustc::mir::mono::MonoItem as rustc_codegen_ssa::mono_item::MonoItemExt>::define
  25: rustc_codegen_llvm::base::compile_codegen_unit::module_codegen
  26: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task
  27: rustc_codegen_llvm::base::compile_codegen_unit
  28: rustc_codegen_ssa::base::codegen_crate
  29: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::CodegenBackend>::codegen_crate
  30: rustc_interface::passes::start_codegen
  31: rustc::ty::context::tls::enter_global
  32: rustc_interface::queries::Queries::ongoing_codegen
  33: rustc_interface::interface::run_compiler_in_existing_thread_pool
  34: rustc_ast::attr::with_globals
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/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.44.0-nightly (75208942f 2020-03-27) 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

query stack during panic:
end of query stack
error: aborting due to previous error

error: could not compile `playground`.

To learn more, run the command again with --verbose.

Edit: This smaller example seems to behave slightly different in that it does produce a (however different) ICE even before nightly-2020-03-25. In the original example when compiling as a library (i.e. “Build” vs “Run”), that other ICE appears before that regression, too.

In other words, the bisection above only applies to the error in this issue’s title – the one that OP got.

Edit2: The error before nightly-2020-03-25 looks a lot like #68596.

For the record:

error before nightly-2020-03-25

warning: the feature `const_generics` is incomplete and may cause the compiler to crash
 --> main.rs:1:12
  |
1 | #![feature(const_generics)]
  |            ^^^^^^^^^^^^^^
  |
  = note: `#[warn(incomplete_features)]` on by default

error: internal compiler error: unexpected const parent in type_of_def_id(): Expr(expr(HirId { owner: DefIndex(8), local_id: 6 }: R.method::<>()))

error: internal compiler error: mir_const_qualif: MIR had errors
 --> main.rs:8:16
  |
8 |     R.method::<1u8>();
  |                ^^^

error: internal compiler error: PromoteTemps: MIR had errors
 --> main.rs:8:16
  |
8 |     R.method::<1u8>();
  |                ^^^

error: internal compiler error: broken MIR in DefId(0:9 ~ main[317d]::main[0]::{{constant}}[0]) ("return type"): bad type [type error]
 --> main.rs:8:16
  |
8 |     R.method::<1u8>();
  |                ^^^

error: internal compiler error: broken MIR in DefId(0:9 ~ main[317d]::main[0]::{{constant}}[0]) (LocalDecl { mutability: Mut, local_info: Other, internal: false, is_block_tail: None, ty: [type error], user_ty: UserTypeProjections { contents: [] }, source_info: SourceInfo { span: main.rs:8:16: 8:19, scope: scope[0] } }): bad type [type error]
 --> main.rs:8:16
  |
8 |     R.method::<1u8>();
  |                ^^^

thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', src\librustc_errors\lib.rs:346:17
stack backtrace:
   0: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
   1: core::fmt::write
   2: <std::io::IoSliceMut as core::fmt::Debug>::fmt
   3: std::panicking::take_hook
   4: std::panicking::take_hook
   5: rustc_driver::report_ice
   6: std::panicking::rust_panic_with_hook
   7: rustc_errors::annotate_snippet_emitter_writer::AnnotateSnippetEmitterWriter::ui_testing
   8: <rustc_errors::HandlerInner as core::ops::drop::Drop>::drop
   9: rustc_driver::pretty::print_after_hir_lowering
  10: rustc_driver::pretty::print_after_hir_lowering
  11: rustc_driver::pretty::print_after_hir_lowering
  12: rustc_driver::pretty::print_after_hir_lowering
  13: <rustc_span::symbol::SymbolStr as core::fmt::Display>::fmt
  14: <env_logger::filter::inner::Filter as core::fmt::Display>::fmt
  15: <env_logger::filter::inner::Filter as core::fmt::Display>::fmt
  16: _rust_maybe_catch_panic
  17: rustc_driver::pretty::print_after_hir_lowering
  18: ZN244_$LT$std..error..$LT$impl$u20$core..convert..From$LT$alloc..string..String$GT$$u20$for$u20$alloc..boxed..Box$LT$dyn$u20$std..error..Error$u2b$core..marker..Sync$u2b$core..marker..Send$GT$$GT$..from..StringError$u20$as$u20$core..fmt..Display$GT$3fmt17
  19: std::sys::windows::thread::Thread::new
  20: BaseThreadInitThunk
  21: RtlUserThreadStart
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

error: internal compiler error: unexpected panic

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 1.42.0-nightly (8a87b945b 2020-01-14) running on x86_64-pc-windows-msvc

query stack during panic:
end of query stack