Const generics: Clippy: "expected bits of usize, got Const"

[andre-richter]

I ran into this error

error: internal compiler error: src/librustc/ty/sty.rs:2355: expected bits of usize, got Const {
    ty: usize,
    val: Param(
        NUM_SPECIAL_RANGES/#0,
    ),
}

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:931:9

Steps to repro:

1. Install Rust nightly
2. cargo install xbuild
3. git clone git@github.com:rust-embedded/rust-raspi3-OS-tutorials.git
4. cd rust-raspi3-OS-tutorials/11_virtual_memory
5. make clippy

It might be about this code:

pub struct KernelVirtualLayout<const NUM_SPECIAL_RANGES: usize> {
    max_virt_addr_inclusive: usize,
    inner: [RangeDescriptor; NUM_SPECIAL_RANGES],
}

impl<const NUM_SPECIAL_RANGES: usize> KernelVirtualLayout<{ NUM_SPECIAL_RANGES }> {
    pub const fn new(max: usize, layout: [RangeDescriptor; NUM_SPECIAL_RANGES]) -> Self {
        Self {
            max_virt_addr_inclusive: max,
            inner: layout,
        }
    }

Meta

rustc 1.40.0-nightly (2477e2493 2019-11-04)
binary: rustc
commit-hash: 2477e2493e67527fc282c7239e019f7ebd513a1a
commit-date: 2019-11-04
host: x86_64-unknown-linux-gnu
release: 1.40.0-nightly
LLVM version: 9.0

Backtrace:

 RUST_BACKTRACE=1 make clippy
cargo xclippy --target=aarch64-unknown-none-softfloat --features bsp_rpi3
    Checking kernel v0.1.0 (/home/arichter/repos/rust-raspi3-OS-tutorials/11_virtual_memory)
error: internal compiler error: src/librustc/ty/sty.rs:2355: expected bits of usize, got Const {
    ty: usize,
    val: Param(
        NUM_SPECIAL_RANGES/#0,
    ),
}

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:931:9
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.40/src/backtrace/libunwind.rs:88
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.40/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print_fmt
             at src/libstd/sys_common/backtrace.rs:77
   3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
             at src/libstd/sys_common/backtrace.rs:61
   4: core::fmt::write
             at src/libcore/fmt/mod.rs:1028
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1412
   6: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:65
   7: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:50
   8: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:188
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:205
  10: rustc_driver::report_ice
  11: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:468
  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_context_opt
  18: rustc::ty::context::tls::with_opt
  19: rustc::util::bug::opt_span_bug_fmt
  20: rustc::util::bug::bug_fmt
  21: rustc::ty::sty::Const::eval_bits::{{closure}}
  22: clippy_lints::loops::check_for_loop
  23: <clippy_lints::loops::Loops as rustc::lint::LateLintPass>::check_expr
  24: <rustc::lint::context::LateLintPassObjects as rustc::lint::LateLintPass>::check_expr
  25: <rustc::lint::context::LateContextAndPass<T> as rustc::hir::intravisit::Visitor>::visit_expr
  26: <rustc::lint::context::LateContextAndPass<T> as rustc::hir::intravisit::Visitor>::visit_expr
  27: rustc::hir::intravisit::walk_block
  28: rustc::hir::intravisit::walk_expr
  29: <rustc::lint::context::LateContextAndPass<T> as rustc::hir::intravisit::Visitor>::visit_expr
  30: <rustc::lint::context::LateContextAndPass<T> as rustc::hir::intravisit::Visitor>::visit_nested_body
  31: <rustc::lint::context::LateContextAndPass<T> as rustc::hir::intravisit::Visitor>::visit_fn
  32: rustc::hir::intravisit::walk_impl_item
  33: rustc::hir::intravisit::Visitor::visit_nested_impl_item
  34: rustc::hir::intravisit::walk_item
  35: rustc::hir::intravisit::Visitor::visit_nested_item
  36: rustc::hir::intravisit::walk_item
  37: rustc::hir::intravisit::Visitor::visit_nested_item
  38: rustc::hir::intravisit::walk_crate
  39: rustc::lint::context::late_lint_pass_crate
  40: rustc::lint::context::late_lint_crate
  41: rustc::util::common::time
  42: rustc::util::common::time
  43: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:78
  44: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
  45: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:78
  46: rustc_interface::passes::analysis::{{closure}}
  47: rustc_interface::passes::analysis
  48: rustc::ty::query::__query_compute::analysis
  49: rustc::dep_graph::graph::DepGraph::with_task_impl
  50: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  51: rustc_interface::passes::BoxedGlobalCtxt::access::{{closure}}
  52: rustc_interface::passes::create_global_ctxt::{{closure}}
  53: rustc_interface::passes::BoxedGlobalCtxt::enter
  54: rustc_interface::interface::run_compiler_in_existing_thread_pool
  55: std::thread::local::LocalKey<T>::with
  56: scoped_tls::ScopedKey<T>::set
  57: syntax::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 1.40.0-nightly (2477e2493 2019-11-04) 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

query stack during panic:
#0 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to previous error

error: could not compile `kernel`.

To learn more, run the command again with --verbose.
Makefile:115: recipe for target 'clippy' failed
make: *** [clippy] Error 101

[Centril]

cc @rust-lang/clippy -- this could probably be transferred to Clippy?

[flip1995]

Here is a minimal reproducer:

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

pub struct ArrayWrapper<const N: usize>([usize; N]);

impl<const N: usize> ArrayWrapper<{ N }> {
    pub fn ice(&self) {
        for i in self.0.iter() {
            println!("{}", i);
        }
    }
}

Playground

[flip1995]

Relevant (debug) backtrace for this:

  21: rustc::ty::sty::Const::eval_bits::{{closure}}
             at /rustc/3f0e16473de5ec010f44290a8c3ea1d90e0ad7a2/src/librustc/macros.rs:44
  22: core::option::Option<T>::unwrap_or_else
             at /rustc/3f0e16473de5ec010f44290a8c3ea1d90e0ad7a2/src/libcore/option.rs:419
  23: rustc::ty::sty::Const::eval_bits
             at /rustc/3f0e16473de5ec010f44290a8c3ea1d90e0ad7a2/src/librustc/ty/sty.rs:2354
  24: rustc::ty::sty::Const::eval_usize
             at /rustc/3f0e16473de5ec010f44290a8c3ea1d90e0ad7a2/src/librustc/ty/sty.rs:2360
  25: clippy_lints::loops::is_iterable_array
             at clippy_lints/src/loops.rs:1996

It tries to call eval_usize on a generic parameter. This is currently not supported. See
https://github.com/rust-lang/rust/blob/3f0e16473de5ec010f44290a8c3ea1d90e0ad7a2/src/librustc/mir/interpret/value.rs#L69-L80

and the ConstValue documentation

---

I think just bailing out, when eval_usize fails is the best thing to do here right now.

[c410-f3r]

Issue still happens in this repository.

error: internal compiler error: src/librustc/ty/sty.rs:2522: expected bits of usize, got Const {
    ty: usize,
    val: Param(
        N/#1,
    ),
}

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:881:9
stack backtrace:
   0:     0x7f8276766644 - backtrace::backtrace::libunwind::trace::h9d5fa1647efe1ab1
                               at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.44/src/backtrace/libunwind.rs:86
   1:     0x7f8276766644 - backtrace::backtrace::trace_unsynchronized::h86fb9c5f1eca30ef
                               at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.44/src/backtrace/mod.rs:66
   2:     0x7f8276766644 - std::sys_common::backtrace::_print_fmt::he9ba33a8eb3eb9ee
                               at src/libstd/sys_common/backtrace.rs:78
   3:     0x7f8276766644 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h5b9c1af25ae7c717
                               at src/libstd/sys_common/backtrace.rs:59
   4:     0x7f827679f7ec - core::fmt::write::h307eb561be2a404c
                               at src/libcore/fmt/mod.rs:1052
   5:     0x7f8276757fa7 - std::io::Write::write_fmt::h9f10c0557c95103f
                               at src/libstd/io/mod.rs:1428
   6:     0x7f827676b435 - std::sys_common::backtrace::_print::h9ba9ae783f57eedf
                               at src/libstd/sys_common/backtrace.rs:62
   7:     0x7f827676b435 - std::sys_common::backtrace::print::hfc2586ace23d36ac
                               at src/libstd/sys_common/backtrace.rs:49
   8:     0x7f827676b435 - std::panicking::default_hook::{{closure}}::hae11ef594f739717
                               at src/libstd/panicking.rs:204
   9:     0x7f827676b176 - std::panicking::default_hook::h91a2179e24328404
                               at src/libstd/panicking.rs:224
  10:     0x563c96f7b591 - clippy_driver::report_clippy_ice::h00b78117f8199052
  11:     0x7f827676bb65 - std::panicking::rust_panic_with_hook::h5394bdfc184d7cc7
                               at src/libstd/panicking.rs:474
  12:     0x7f82795865d3 - std::panicking::begin_panic::h586c0171fbdab168
  13:     0x7f82795c2a10 - rustc_errors::HandlerInner::bug::hca42a38f4a7f5b9a
  14:     0x7f82795c1860 - rustc_errors::Handler::bug::he56a55254aefe7ac
  15:     0x7f82792b2d29 - rustc::util::bug::opt_span_bug_fmt::{{closure}}::hcf8a9328b7d9651c
  16:     0x7f82792a90bb - rustc::ty::context::tls::with_opt::{{closure}}::hc97cc9e8bd8ae5d8
  17:     0x7f82792a9062 - rustc::ty::context::tls::with_opt::hc754df500ae2375b
  18:     0x7f82792b2c38 - rustc::util::bug::opt_span_bug_fmt::h7906b53d89b4c2e1
  19:     0x7f82792b2ba2 - rustc::util::bug::bug_fmt::hd3ba947be3f6a8df
  20:     0x563c96f9f47f - rustc::ty::sty::Const::eval_bits::{{closure}}::he6bca075ade2f14a
  21:     0x563c96fb1f47 - <clippy_lints::indexing_slicing::IndexingSlicing as rustc_lint::passes::LateLintPass>::check_expr::hc5e15fc7d2e672c0
  22:     0x7f8278973e43 - <rustc_lint::late::LateLintPassObjects as rustc_lint::passes::LateLintPass>::check_expr::hf6d54270d843a380
  23:     0x7f827702c6e2 - <rustc_lint::late::LateContextAndPass<T> as rustc_hir::intravisit::Visitor>::visit_expr::h9f4179d7d857c919
  24:     0x7f8276fc6686 - rustc_hir::intravisit::walk_expr::he754354f137a537e
  25:     0x7f827702c6ed - <rustc_lint::late::LateContextAndPass<T> as rustc_hir::intravisit::Visitor>::visit_expr::h9f4179d7d857c919
  26:     0x7f8276fc6882 - rustc_hir::intravisit::walk_expr::he754354f137a537e
  27:     0x7f827702c6ed - <rustc_lint::late::LateContextAndPass<T> as rustc_hir::intravisit::Visitor>::visit_expr::h9f4179d7d857c919
  28:     0x7f8276fc4bf4 - rustc_hir::intravisit::walk_fn::h3ff39dabd4ec61b9
  29:     0x7f827702d8a8 - <rustc_lint::late::LateContextAndPass<T> as rustc_hir::intravisit::Visitor>::visit_fn::hbb0b96ca91285ee7
  30:     0x7f8276fc226b - rustc_hir::intravisit::walk_impl_item::h598229146e9414df
  31:     0x7f827702ed5a - rustc_hir::intravisit::Visitor::visit_nested_impl_item::hdf4d97b76cbfda60
  32:     0x7f8276fc79d0 - rustc_hir::intravisit::walk_item::h44e80ad5b6277e08
  33:     0x7f827702e470 - rustc_hir::intravisit::Visitor::visit_nested_item::h290b2b9ac183f311
  34:     0x7f8276fc706e - rustc_hir::intravisit::walk_item::h44e80ad5b6277e08
  35:     0x7f827702e470 - rustc_hir::intravisit::Visitor::visit_nested_item::h290b2b9ac183f311
  36:     0x7f8276fc126e - rustc_hir::intravisit::walk_crate::h68de15a1d07fe82c
  37:     0x7f827701fecd - rustc_lint::late::late_lint_pass_crate::he7676702f03bb31a
  38:     0x7f827701f6eb - rustc_lint::late::late_lint_crate::h303b0802dd8c9a09
  39:     0x7f8276fde60b - rustc_data_structures::sync::join::hf5650324bb2ed613
  40:     0x7f8277020c9b - std::panicking::try::do_call::he8ffa9e7e95783d2
  41:     0x7f827677d457 - __rust_maybe_catch_panic
                               at src/libpanic_unwind/lib.rs:86
  42:     0x7f8276fd9413 - <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once::hf6c4f0787ce2bd29
  43:     0x7f827677d457 - __rust_maybe_catch_panic
                               at src/libpanic_unwind/lib.rs:86
  44:     0x7f8276fdc60a - rustc_session::utils::<impl rustc_session::session::Session>::time::h7249262b0ade9d94
  45:     0x7f827705aa36 - rustc_interface::passes::analysis::h63a5c50615a3546c
  46:     0x7f8276df5616 - rustc::ty::query::__query_compute::analysis::h7f7df2982d90698a
  47:     0x7f8276e5cc21 - rustc::dep_graph::graph::DepGraph::with_task_impl::h3547b6b631c468ed
  48:     0x7f8276e327d0 - rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query::hc2385fc085b423d4
  49:     0x7f8276e6c577 - rustc::ty::context::tls::enter_global::h8350ae2f23d40602
  50:     0x7f8276e3ed97 - rustc_interface::interface::run_compiler_in_existing_thread_pool::hc7ccb7d92618cd77
  51:     0x7f8276df0394 - std::sys_common::backtrace::__rust_begin_short_backtrace::h4e648e17f1d26b8c
  52:     0x7f827677d457 - __rust_maybe_catch_panic
                               at src/libpanic_unwind/lib.rs:86
  53:     0x7f8276e40796 - core::ops::function::FnOnce::call_once{{vtable.shim}}::h34b4c1a65012f088
  54:     0x7f827674832f - <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once::h558ce43155c9780d
                               at /rustc/436494b8f8008b600d64b3951f63c2bb0ea81673/src/liballoc/boxed.rs:1017
  55:     0x7f827677bd60 - <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once::hb6d9c1adc82281fd
                               at /rustc/436494b8f8008b600d64b3951f63c2bb0ea81673/src/liballoc/boxed.rs:1017
  56:     0x7f827677bd60 - std::sys_common::thread::start_thread::hcd78bb6c3dec167d
                               at src/libstd/sys_common/thread.rs:13
  57:     0x7f827677bd60 - std::sys::unix::thread::Thread::new::thread_start::h1c16950397532ea6
                               at src/libstd/sys/unix/thread.rs:80
  58:     0x7f82766ce669 - start_thread
  59:     0x7f82765dc323 - clone
  60:                0x0 - <unknown>

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 (8fbb23f 2020-02-21)

query stack during panic:
#0 [analysis] running analysis passes on this crate
end of query stack

[flip1995]

That is another ICE. Can you open a separate issue?

[c410-f3r]

Sure