ICE(stable): thread 'rustc' panicked at 'called `Option::unwrap()` on a `None` value', compiler/rustc_middle/src/ty/instance.rs:434:85

[fominok]

Code

EDIT: MCVE is here.

use core::fmt::Debug;
use futures::future::BoxFuture;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let dependency = "dependency".to_owned();
    let storage = InMemoryStorage;
    run(&dependency, storage).await;
    Ok(())
}

pub(crate) struct InMemoryStorage;

struct User<'dep> {
    name: String,
    dep: &'dep str,
}

impl<'a> StorageRequest<InMemoryStorage> for SaveUser<'a> {
    fn execute(
        &self,
        storage: &InMemoryStorage,
    ) -> BoxFuture<
        Result<<Self as StorageRequestReturnType>::Output, <InMemoryStorage as Storage>::Error>,
    > {
        todo!()
    }
}

trait Storage {
    type Error;
}

impl Storage for InMemoryStorage {
    type Error = String;
}

trait StorageRequestReturnType {
    type Output;
}

trait StorageRequest<S: Storage>: StorageRequestReturnType {
    fn execute(
        &self,
        storage: &S,
    ) -> BoxFuture<Result<<Self as StorageRequestReturnType>::Output, <S as Storage>::Error>>;
}

struct SaveUser<'a> {
    name: &'a str,
}

impl<'a> StorageRequestReturnType for SaveUser<'a> {
    type Output = ();
}

impl<'dep> User<'dep> {
    async fn new<S>(storage: &S, dep: &'dep str) -> User<'dep>
    where
        S: Storage,
    {
        User {
            dep,
            name: "Joe".to_owned(),
        }
    }

    async fn save<S>(mut self, storage: &S)
    where
        S: Storage,
        for<'a> SaveUser<'a>: StorageRequest<S>,
        <S as Storage>::Error: Debug,
    {
        SaveUser { name: &self.name }
            .execute(storage)
            .await
            .unwrap();
    }
}

async fn run<S>(dep: &'_ str, storage: S)
where
    S: Storage,
    <S as Storage>::Error: Debug,
    for<'a> SaveUser<'a>: StorageRequest<S>,
{
    let user = User::new(&storage, dep).await;
    user.save(&storage).await;
}

Meta

Also reproducible on beta and nightly;

rustc --version --verbose:

rustc 1.49.0 (e1884a8e3 2020-12-29)
binary: rustc
commit-hash: e1884a8e3c3e813aada8254edfa120e85bf5ffca
commit-date: 2020-12-29
host: x86_64-unknown-linux-gnu
release: 1.49.0

Error output

thread 'rustc' panicked at 'called `Option::unwrap()` on a `None` value', compiler/rustc_middle/src/ty/instance.rs:434:85
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/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.49.0 (e1884a8e3 2020-12-29) running on x86_64-unknown-linux-gnu

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 [collect_and_partition_mono_items] collect_and_partition_mono_items
end of query stack

Backtrace

thread 'rustc' panicked at 'called `Option::unwrap()` on a `None` value', compiler/rustc_middle/src/ty/instance.rs:434:85
stack backtrace:
   0: rust_begin_unwind
             at /rustc/e1884a8e3c3e813aada8254edfa120e85bf5ffca/library/std/src/panicking.rs:495:5
   1: core::panicking::panic_fmt
             at /rustc/e1884a8e3c3e813aada8254edfa120e85bf5ffca/library/core/src/panicking.rs:92:14
   2: core::panicking::panic
             at /rustc/e1884a8e3c3e813aada8254edfa120e85bf5ffca/library/core/src/panicking.rs:50:5
   3: rustc_middle::ty::instance::Instance::resolve_drop_in_place
   4: <rustc_mir::monomorphize::collector::MirNeighborCollector as rustc_middle::mir::visit::Visitor>::visit_terminator
   5: rustc_mir::monomorphize::collector::collect_neighbours
   6: rustc_mir::monomorphize::collector::collect_items_rec
   7: rustc_mir::monomorphize::collector::collect_items_rec
   8: rustc_mir::monomorphize::collector::collect_items_rec
   9: rustc_mir::monomorphize::collector::collect_items_rec
  10: rustc_mir::monomorphize::collector::collect_items_rec
  11: rustc_mir::monomorphize::collector::collect_items_rec
  12: rustc_mir::monomorphize::collector::collect_items_rec
  13: rustc_mir::monomorphize::collector::collect_items_rec
  14: rustc_mir::monomorphize::collector::collect_items_rec
  15: rustc_mir::monomorphize::collector::collect_items_rec
  16: rustc_mir::monomorphize::collector::collect_items_rec
  17: rustc_mir::monomorphize::collector::collect_items_rec
  18: rustc_mir::monomorphize::collector::collect_items_rec
  19: rustc_mir::monomorphize::collector::collect_items_rec
  20: rustc_mir::monomorphize::collector::collect_items_rec
  21: rustc_mir::monomorphize::collector::collect_items_rec
  22: rustc_mir::monomorphize::collector::collect_items_rec
  23: rustc_mir::monomorphize::collector::collect_items_rec
  24: rustc_mir::monomorphize::collector::collect_items_rec
  25: rustc_session::utils::<impl rustc_session::session::Session>::time
  26: rustc_mir::monomorphize::collector::collect_crate_mono_items
  27: rustc_mir::monomorphize::partitioning::collect_and_partition_mono_items
  28: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::collect_and_partition_mono_items>::compute
  29: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  30: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  31: rustc_data_structures::stack::ensure_sufficient_stack
  32: rustc_query_system::query::plumbing::get_query_impl
  33: rustc_codegen_ssa::base::codegen_crate
  34: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::CodegenBackend>::codegen_crate
  35: rustc_interface::passes::QueryContext::enter
  36: rustc_interface::queries::Queries::ongoing_codegen
  37: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  38: rustc_span::with_source_map
  39: rustc_interface::interface::create_compiler_and_run
  40: rustc_span::with_session_globals
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/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.49.0 (e1884a8e3 2020-12-29) running on x86_64-unknown-linux-gnu

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 [collect_and_partition_mono_items] collect_and_partition_mono_items
end of query stack

[jyn514]

Slightly smaller:

use futures::future::BoxFuture;

fn main() {
    f();
}

#[tokio::main]
async fn f() {
    run("dependency").await;
}

struct InMemoryStorage;

struct User<'dep> {
    dep: &'dep str,
}

impl<'a> StorageRequest<InMemoryStorage> for SaveUser<'a> {
    fn execute(&self) -> BoxFuture<Result<(), String>> {
        todo!()
    }
}

trait Storage {
    type Error;
}

impl Storage for InMemoryStorage {
    type Error = String;
}

trait StorageRequestReturnType {
    type Output;
}

trait StorageRequest<S: Storage>: StorageRequestReturnType {
    fn execute(
        &self,
    ) -> BoxFuture<Result<<Self as StorageRequestReturnType>::Output, <S as Storage>::Error>>;
}

struct SaveUser<'a> {
    name: &'a str,
}

impl<'a> StorageRequestReturnType for SaveUser<'a> {
    type Output = ();
}

impl<'dep> User<'dep> {
    async fn save<S>(self)
    where
        S: Storage,
        for<'a> SaveUser<'a>: StorageRequest<S>,
    {
        SaveUser { name: "Joe" }
            .execute()
            .await;
    }
}

async fn run<S>(dep: &str)
where
    S: Storage,
    for<'a> SaveUser<'a>: StorageRequest<S>,
{
    User { dep }.save().await;
}

There are a few strange things about this:

1. If you remove .await from async fn f(), or if you remove tokio::main, it gives a different ICE:

error: internal compiler error: compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs:228:13: debuginfo: Trying to create type name for unexpected type: <SaveUser as StorageRequestReturnType>::Output

thread 'rustc' panicked at 'Box<Any>', compiler/rustc_errors/src/lib.rs:958:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Backtrace

error: internal compiler error: compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs:228:13: debuginfo: Trying to create type name for unexpected type: <SaveUser as StorageRequestReturnType>::Output

thread 'rustc' panicked at 'Box<Any>', compiler/rustc_errors/src/lib.rs:958:9
stack backtrace:
   0: std::panicking::begin_panic
   1: rustc_errors::HandlerInner::bug
   2: rustc_errors::Handler::bug
   3: rustc_middle::ty::context::tls::with_opt
   4: rustc_middle::util::bug::opt_span_bug_fmt
   5: rustc_middle::util::bug::bug_fmt
   6: rustc_codegen_ssa::debuginfo::type_names::push_debuginfo_type_name
   7: rustc_codegen_ssa::debuginfo::type_names::push_debuginfo_type_name::push_type_params
   8: rustc_codegen_ssa::debuginfo::type_names::compute_debuginfo_type_name
   9: rustc_codegen_llvm::debuginfo::metadata::prepare_enum_metadata
  10: rustc_codegen_llvm::debuginfo::metadata::type_metadata
  11: rustc_codegen_llvm::debuginfo::<impl rustc_codegen_ssa::traits::debuginfo::DebugInfoMethods for rustc_codegen_llvm::context::CodegenCx>::create_dbg_var
  12: rustc_codegen_ssa::mir::codegen_mir
  13: rustc_codegen_ssa::base::codegen_instance
  14: <rustc_middle::mir::mono::MonoItem as rustc_codegen_ssa::mono_item::MonoItemExt>::define
  15: rustc_codegen_llvm::base::compile_codegen_unit::module_codegen
  16: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  17: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task
  18: rustc_codegen_llvm::base::compile_codegen_unit
  19: rustc_codegen_ssa::base::codegen_crate
  20: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::CodegenBackend>::codegen_crate
  21: rustc_session::utils::<impl rustc_session::session::Session>::time
  22: rustc_interface::passes::QueryContext::enter
  23: rustc_interface::queries::Queries::ongoing_codegen
  24: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  25: rustc_span::with_source_map
  26: rustc_interface::interface::create_compiler_and_run
  27: rustc_span::with_session_globals
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

query stack during panic:
end of query stack

2. If you make any of the functions unreachable, it compiles fine. Presumably the compiler notices they're unused and don't need to be monomorphized.
3. If you change the trait definition of fn execute to remove the associated items and return Result<(), String> instead, it compiles fine.
4. If you remove async fn run and manually inline it into f, it compiles fine.

[jyn514]

Relevant code:

rust/compiler/rustc_middle/src/ty/instance.rs

Line 434 in 9919ad6

Instance::resolve(tcx, ty::ParamEnv::reveal_all(), def_id, substs).unwrap().unwrap()

rust/compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs

Lines 221 to 233 in 9919ad6

	ty::Error(_)
	| ty::Infer(_)
	| ty::Placeholder(..)
	| ty::Projection(..)
	| ty::Bound(..)
	| ty::Opaque(..)
	| ty::GeneratorWitness(..) => {
	bug!(
	"debuginfo: Trying to create type name for \
	unexpected type: {:?}",
	t
	);
	}

[fominok]

Removing 'dep still gives ICE, that's weird as I left it intentionally because previously it was required to reproduce; anyway it can be removed now to simplify the example

Edit: Should it be labeled with some priority as it is an ICE on Stable?

[jyn514]

@fominok can you remove 'dep and post the new code? I don't have time right now.

Edit: Should it be labeled with some priority as it is an ICE on Stable?

Normally issues aren't prioritized unless they're regressions or unsound, but I can make an exception since you asked nicely :)

[fominok]

@jyn514 it's up to you, but many thanks anyway!

I just tried to remove 'dep for a simplified example you posted and it compiles, but it doesn't compile for a snippet I posted first, so here is a version that sill larger than yours, but without lifetime parameter for a User struct:

use core::fmt::Debug;
use futures::future::BoxFuture;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let storage = InMemoryStorage;
    run(storage).await;
    Ok(())
}

pub(crate) struct InMemoryStorage;

struct User {
    name: String,
}

impl<'a> StorageRequest<InMemoryStorage> for SaveUser<'a> {
    fn execute(
        &self,
        storage: &InMemoryStorage,
    ) -> BoxFuture<
        Result<<Self as StorageRequestReturnType>::Output, <InMemoryStorage as Storage>::Error>,
    > {
        todo!()
    }
}

trait Storage {
    type Error;
}

impl Storage for InMemoryStorage {
    type Error = String;
}

trait StorageRequestReturnType {
    type Output;
}

trait StorageRequest<S: Storage>: StorageRequestReturnType {
    fn execute(
        &self,
        storage: &S,
    ) -> BoxFuture<Result<<Self as StorageRequestReturnType>::Output, <S as Storage>::Error>>;
}

struct SaveUser<'a> {
    name: &'a str,
}

impl<'a> StorageRequestReturnType for SaveUser<'a> {
    type Output = ();
}

impl User {
    async fn new<S>(storage: &S) -> User
    where
        S: Storage,
    {
        User {
            name: "Joe".to_owned(),
        }
    }

    async fn save<S>(mut self, storage: &S)
    where
        S: Storage,
        for<'a> SaveUser<'a>: StorageRequest<S>,
        <S as Storage>::Error: Debug,
    {
        SaveUser { name: &self.name }
            .execute(storage)
            .await
            .unwrap();
    }
}

async fn run<S>(storage: S)
where
    S: Storage,
    <S as Storage>::Error: Debug,
    for<'a> SaveUser<'a>: StorageRequest<S>,
{
    let user = User::new(&storage).await;
    user.save(&storage).await;
}

[SNCPlay42]

Turns out this is a regression: the code works on 1.47 and ICEs on 1.48.

searched nightlies: from nightly-2020-08-24 to nightly-2020-11-14
regressed nightly: nightly-2020-11-09
searched commits: from b2d115f to 1773f60
regressed commit: 87a0997 (#78410, backported to 1.48 in #78783)

bisected with cargo-bisect-rustc v0.6.0

Host triple: x86_64-unknown-linux-gnu
Reproduce with:

cargo bisect-rustc --preserve --start=2020-08-24 --end=2020-11-14 -- build 

@rustbot label regression-from-stable-to-stable

also, since no-one's posted a reduction without the use of async/await:

@rustbot label A-async-await