'rustc' panicked at 'internal error: entered unreachable code', src/libsyntax/ast.rs:668:6 while bootstrapping

[matthiaskrgr]

git checkout 02f5786
./x.py build
git checkout f492693
./x.py build
=> ICE'd

Click for build log and stack trace

Updating only changed submodules
Submodules updated in 0.02 seconds
    Finished dev [unoptimized] target(s) in 0.28s
Building stage0 std artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
    Finished release [optimized] target(s) in 0.34s
Copying stage0 std from stage0 (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu / x86_64-unknown-linux-gnu)
Building stage0 test artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
    Finished release [optimized] target(s) in 0.28s
Copying stage0 test from stage0 (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu / x86_64-unknown-linux-gnu)
Building stage0 compiler artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
    Finished release [optimized] target(s) in 0.33s
Copying stage0 rustc from stage0 (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu / x86_64-unknown-linux-gnu)
Building stage0 codegen artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu, llvm)
    Finished release [optimized] target(s) in 0.30s
Assembling stage1 compiler (x86_64-unknown-linux-gnu)
Building stage1 std artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
    Finished release [optimized] target(s) in 0.39s
Copying stage1 std from stage1 (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu / x86_64-unknown-linux-gnu)
Building stage1 test artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
    Finished release [optimized] target(s) in 0.39s
Copying stage1 test from stage1 (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu / x86_64-unknown-linux-gnu)
Building stage1 compiler artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
   Compiling serde_json v1.0.33
   Compiling syn v0.15.22
   Compiling rls-data v0.19.0
   Compiling rustc-rayon v0.2.0
   Compiling rand v0.6.1
   Compiling parking_lot_core v0.4.0
   Compiling tempfile v3.0.5
thread 'rustc' panicked at 'internal error: entered unreachable code', src/libsyntax/ast.rs:668:66ore, tempfile
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
   1: std::sys_common::backtrace::print
   2: std::panicking::default_hook::{{closure}}
   3: std::panicking::default_hook
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
   6: std::panicking::begin_panic
   7: serialize::serialize::Decoder::read_struct
   8: serialize::serialize::Decoder::read_enum
   9: serialize::serialize::Decoder::read_struct
  10: <alloc::boxed::Box<T> as serialize::serialize::Decodable>::decode
  11: serialize::serialize::Decoder::read_enum
  12: serialize::serialize::Decoder::read_seq
  13: <rustc::mir::TerminatorKind as serialize::serialize::Decodable>::decode::{{closure}}::{{closure}}
  14: serialize::serialize::Decoder::read_struct
  15: serialize::serialize::Decoder::read_option
  16: serialize::serialize::Decoder::read_struct
  17: serialize::serialize::Decoder::read_seq
  18: <rustc::mir::Mir as serialize::serialize::Decodable>::decode::{{closure}}
  19: rustc_metadata::decoder::<impl rustc_metadata::schema::Lazy<T>>::decode
  20: rustc_metadata::cstore_impl::provide_extern::optimized_mir
  21: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::optimized_mir>::compute
  22: rustc::dep_graph::graph::DepGraph::with_task_impl
  23: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  24: rustc_mir::monomorphize::collector::collect_items_rec
  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_mir::monomorphize::collector::collect_items_rec
  29: rustc_mir::monomorphize::collector::collect_crate_mono_items::{{closure}}
  30: rustc::util::common::time
  31: rustc_mir::monomorphize::collector::collect_crate_mono_items
  32: rustc::util::common::time
  33: rustc_mir::monomorphize::partitioning::collect_and_partition_mono_items
  34: rustc::ty::query::__query_compute::collect_and_partition_mono_items
  35: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::collect_and_partition_mono_items>::compute
  36: rustc::dep_graph::graph::DepGraph::with_task_impl
  37: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  38: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_utils::codegen_backend::CodegenBackend>::codegen_crate
  39: rustc::util::common::time
  40: rustc_interface::passes::start_codegen
  41: rustc::ty::context::tls::enter_global
  42: rustc_interface::passes::BoxedGlobalCtxt::access::{{closure}}
  43: rustc_interface::passes::create_global_ctxt::{{closure}}
  44: rustc_interface::passes::BoxedGlobalCtxt::enter
  45: rustc_interface::queries::Query<T>::compute
  46: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::ongoing_codegen
  47: rustc_interface::interface::run_compiler_in_existing_thread_pool
  48: std::thread::local::LocalKey<T>::with
  49: scoped_tls::ScopedKey<T>::set
  50: syntax::with_globals
query stack during panic:
#0 [optimized_mir] processing `<proc_macro2::stable::Ident as std::cmp::PartialEq<T>>::eq`
#1 [collect_and_partition_mono_items] collect_and_partition_mono_items
end of query stack

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 1.36.0-dev running on x86_64-unknown-linux-gnu

note: compiler flags: -Z unstable-options -Z force-unstable-if-unmarked -C opt-level=2 -C debuginfo=0 --crate-type lib

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

error: Could not compile `syn`.
warning: build failed, waiting for other jobs to finish...
error: build failed
command did not execute successfully: "/home/matthias/vcs/github/rust/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "build" "--target" "x86_64-unknown-linux-gnu" "-j" "4" "--release" "--features" "" "--manifest-path" "/home/matthias/vcs/github/rust/src/rustc/Cargo.toml" "--message-format" "json"
expected success, got: exit code: 101
failed to run: /home/matthias/vcs/github/rust/build/bootstrap/debug/bootstrap build
Build completed unsuccessfully in 0:00:15

config.toml:

[llvm]
[build]
submodules = true
extended = true
tools = ["cargo", "rls", "clippy", "rustfmt", "analysis", "src"]
sanitizers = true
profiler = true
low-priority = true
[install]
[rust]
[target.x86_64-unknown-linux-gnu]
[dist]

[matthiaskrgr]

I retried the recipe with a clean build now and could not reproduce... :/
Could this be a another incremental compilation related bug?

[hellow554]

This sounds like a incremental bug, but I can't see that you are using incremental compiling (neither incremental = true in your config.toml, nor the -i switch in your x.py build), so I guess it isn't. Must be something else?!

[pnkfelix]

@hellow554 Isn't incremental turned on by default at this point? (Is that only for debug builds? We do not know from this bug report whether this is a debug build or not... oh, they included their config.toml at the bottom, and it does not have debug = true ... so I would assume that there is no incremental compilation involved here. Odd...)

[pnkfelix]

hmm, re-reading #60228, it seems like that has the same config.toml that is being used here.

Am I simply incorrect about (or more charitably, "mis-remembering") when our rustbuild bootstrap process will use incremental compilation?

[pnkfelix]

triage: Not sure there is any action we can take here, given that this bug might not be readily reproducible.

I'm going to assign priority P-medium and assign to self, with intent to close as not-reproducible if I cannot reproduce it within a week or so.

[matthiaskrgr]

Well, I hit these "ICE while bootstrapping, but x.py clean ; x.py build makes it disappear" bugs almost daily :/

[pnkfelix]

@matthiaskrgr right, I understand that (and inferred as much from your bug report history).

To be clear, I am planning to leave open the bugs where we have enough information to actually reproduce the issue at hand, such as #60228.

[pnkfelix]

@matthiaskrgr or is your response regarding the priority assignment of P-medium? I suppose I could mark it P-high with the same intent to close...

[pnkfelix]

Okay I talked myself into marking as P-high just so I don't let this slide too long.

[pnkfelix]

I tried to reproduce locally, and like @matthiaskrgr , I was not able to do so on a clean build. Presumably the problem stems from something with old build artifacts.

Closing as non-reproducible. We should instead focus our efforts on either resolving the issues where we have enough information to reproduce (like #60228), or on finding a replacement for rustbuild.