Rustc panics(in some cases) when repr(aligned) struct is used in struct with repr(packed) attribute

[inseo-oh]

I was writing some code that does some x86 page table configuration, but then I noticed that Rust compiler started to panic with this code:

extern crate x86_64;

fn main() {
    use x86_64::structures::paging::page_table::PageTable;

    #[repr(C, packed)]
    struct SomeStruct {
        page_table: PageTable,
    }
}

And I did realize that I cannot use packed in SomeStruct since PageTable has align(4096) attribute. If I rewrite the above code without x86_64 crate:

fn main() {
    //use x86_64::structures::paging::page_table::PageTable;

    #[repr(transparent)]
    struct PageTableEntry {
        entry: u64,
    }

    #[repr(align(4096))]
    #[repr(C)]
    struct PageTable {
        entries: [PageTableEntry; 512],
    }

    #[repr(C, packed)]
    struct SomeStruct {
        page_table: PageTable,
    }
}

(Note that this is basically same thing as x86_64's PageTable struct)

This compiler error is displayed, which is normal:

   Compiling tester v0.1.0 (/home/pi/dandelion/tester)
error[E0588]: packed type cannot transitively contain a `#[repr(align)]` type
  --> src/main.rs:17:5
   |
17 | /     struct SomeStruct {
18 | |         page_table: PageTable,
19 | |     }
   | |_____^
   |
note: `PageTable` has a `#[repr(align)]` attribute
  --> src/main.rs:12:5
   |
12 | /     struct PageTable {
13 | |         entries: [PageTableEntry; 512],
14 | |     }
   | |_____^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0588`.
error: could not compile `tester`.

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

And here's output from RUST_BACKTRACE=1 cargo build --verbose(In this case, I'm trying to compile the first code):

       Fresh bit_field v0.9.0
       Fresh bitflags v1.2.1
       Fresh x86_64 v0.11.0
   Compiling tester v0.1.0 (/home/pi/dandelion/tester)
     Running `rustc --crate-name tester --edition=2018 src/main.rs --error-format=json --json=diagnostic-rendered-ansi --crate-type bin --emit=dep-info,link -Cembed-bitcode=no -C debuginfo=2 -C metadata=3bcfa379acd4179e -C extra-filename=-3bcfa379acd4179e --out-dir /home/pi/dandelion/tester/target/debug/deps -C incremental=/home/pi/dandelion/tester/target/debug/incremental -L dependency=/home/pi/dandelion/tester/target/debug/deps --extern x86_64=/home/pi/dandelion/tester/target/debug/deps/libx86_64-a59195eee3b7016f.rlib`
thread 'rustc' panicked at 'DefId::expect_local: `DefId(15:482 ~ x86_64[835c]::structures[0]::paging[0]::page_table[0]::PageTable[0])` isn't local', /rustc/0262de554b4c4c5af346137bbb1664a3f6cf4df2/src/libstd/macros.rs:16:9
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/git.luolix.top-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/libunwind.rs:86
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/git.luolix.top-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:1076
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1537
   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:481
  12: rust_begin_unwind
             at src/libstd/panicking.rs:385
  13: std::panicking::begin_panic_fmt
             at src/libstd/panicking.rs:339
  14: rustc_span::def_id::DefId::expect_local::{{closure}}
  15: rustc_typeck::check::check_packed
  16: rustc_typeck::check::check_item_type
  17: rustc_middle::hir::map::Map::visit_item_likes_in_module
  18: rustc_typeck::check::check_mod_item_types
  19: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::check_mod_item_types>::compute
  20: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  21: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  22: rustc_data_structures::stack::ensure_sufficient_stack
  23: rustc_query_system::query::plumbing::get_query_impl
  24: rustc_query_system::query::plumbing::ensure_query_impl
  25: rustc_typeck::check_crate
  26: rustc_interface::passes::analysis
  27: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::analysis>::compute
  28: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  29: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  30: rustc_query_system::query::plumbing::get_query_impl
  31: rustc_middle::ty::context::tls::enter_global
  32: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  33: rustc_span::with_source_map
  34: rustc_interface::interface::run_compiler_in_existing_thread_pool
  35: scoped_tls::ScopedKey<T>::set
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 1.46.0-nightly (0262de554 2020-06-07) running on armv7-unknown-linux-gnueabihf

note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental --crate-type bin

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

query stack during panic:
#0 [check_mod_item_types] checking item types in top-level module
#1 [analysis] running analysis passes on this crate
end of query stack
error: could not compile `tester`.

Caused by:
  process didn't exit successfully: `rustc --crate-name tester --edition=2018 src/main.rs --error-format=json --json=diagnostic-rendered-ansi --crate-type bin --emit=dep-info,link -Cembed-bitcode=no -C debuginfo=2 -C metadata=3bcfa379acd4179e -C extra-filename=-3bcfa379acd4179e --out-dir /home/pi/dandelion/tester/target/debug/deps -C incremental=/home/pi/dandelion/tester/target/debug/incremental -L dependency=/home/pi/dandelion/tester/target/debug/deps --extern x86_64=/home/pi/dandelion/tester/target/debug/deps/libx86_64-a59195eee3b7016f.rlib` (exit code: 101)

Looking at the backtrace, there's check_packed function and expect_local:

  14: rustc_span::def_id::DefId::expect_local::{{closure}}
  15: rustc_typeck::check::check_packed

While there's no line number(since the compiler is installed using rustup), thankfully there are only two calls to expect_local inside check_packed. And it seems like the first one is panicking since normal output has nothing more than note: `PageTable` has a `#[repr(align)]` attribute, but I might be wrong.

rust/src/librustc_typeck/check/mod.rs

Line 2480 in 9c1857f

let hir_id = hir.as_local_hir_id(def_spans[0].0.expect_local());

I ran rustup update about five minutes ago before submitting this issue, but result was the same.

BTW: I initially found this bug in Clippy, but then I noticed that Rustc was doing the same thing.

Version

pi@miz:~/dandelion/tester $ rustc --version --verbose
rustc 1.46.0-nightly (0262de554 2020-06-07)
binary: rustc
commit-hash: 0262de554b4c4c5af346137bbb1664a3f6cf4df2
commit-date: 2020-06-07
host: armv7-unknown-linux-gnueabihf
release: 1.46.0-nightly
LLVM version: 10.0

[LeSeulArtichaut]

Assigning P-medium as discussed as part of the Prioritization WG procedure.

[fanninpm]

I can't reproduce this in the Playground. Would you please try this again for us?

[inseo-oh]

I can't reproduce this in the Playground. Would you please try this again for us?

The second one is one that does not panic rustc(The code that panics rustc is the first one). It is very similar to the first one except that it does not use external crate, and compiling it shows the error I was expecting.

Also, the second code was one of my attempts to reproduce the same panic without external crate, but for some reason, it didn't panic the compiler. Only the first code does.