ICE with doc comment on for loop

[kayabaNerve]

Code

#![cfg_attr(not(feature = "std"), no_std)]

use ink_lang as ink;

#[ink::contract(env = serai_extension::SeraiEnvironment)]
mod multisig {
  use scale::Encode;

  use ink_storage::{traits::SpreadAllocate, Mapping};
  use ink_env::{hash::Blake2x256, hash_encoded};

  /// A contract which tracks the current multisig keys.
  #[ink(storage)]
  #[derive(SpreadAllocate)]
  pub struct Multisig {
    /// Validator set currently holding the multisig.
    validator_set: [u8; 32],
    /// Mapping from a curve's index to the multisig's current public key for it.
    // This is a mapping due to ink's eager loading. Considering we're right now only considering
    // secp256k1 and Ed25519, it may be notably more efficient to use a Vec here.
    keys: Mapping<u8, Vec<u8>>,
    /// Voter + Keys -> Voted already or not
    voted: Mapping<(AccountId, [u8; 32]), ()>,
    /// Validator Set + Keys -> Vote Count
    votes: Mapping<([u8; 32], [u8; 32]), u16>,
  }

  /// Event emitted when a new set of multisig keys is voted on. Only for the first vote on a set
  // of keys will they be present in this event.
  #[ink(event)]
  pub struct Vote {
    /// Validator who issued the vote.
    #[ink(topic)]
    validator: AccountId,
    /// Validator set for which keys are being generated.
    #[ink(topic)]
    validator_set: [u8; 32],
    /// Hash of the keys voted on.
    #[ink(topic)]
    hash: [u8; 32],
    /// Keys voted on.
    keys: Option<Vec<Vec<u8>>>,
  }

  /// Event emitted when the new keys are fully generated for all curves, having been fully voted
  /// on.
  #[ink(event)]
  pub struct KeyGen {
    #[ink(topic)]
    hash: [u8; 32],
  }

  /// The Multisig error types.
  #[derive(Debug, PartialEq, Eq, scale::Encode, scale::Decode)]
  #[cfg_attr(feature = "std", derive(scale_info::TypeInfo))]
  pub enum Error {
    /// Returned if a curve index doesn't have a key registered for it.
    NonExistentCurve,
    /// Returned if a non-validator is voting.
    NotValidator,
    /// Returned if this validator set already generated keys.
    AlreadyGeneratedKeys,
    /// Returned if this validator has already voted for these keys.
    AlreadyVoted,
  }

  /// The Multisig result type.
  pub type Result<T> = core::result::Result<T, Error>;

  impl Multisig {
    /// Deploys the Multisig contract.
    #[ink(constructor)]
    pub fn new() -> Self {
      ink_lang::utils::initialize_contract(|_| {})
    }

    /// Validator set currently holding the multisig.
    #[ink(message)]
    pub fn validator_set(&self) -> [u8; 32] {
      self.validator_set
    }

    /// Returns the key currently in-use for a given curve ID. This is then bound to a given chain
    /// by applying a personalized additive offset, as done by the processor. Each chain then has
    /// its own way of receiving funds to these keys, leaving this not for usage by wallets, nor
    /// the processor which is expected to track events for this information. This is really solely
    /// for debugging purposes.
    #[ink(message)]
    pub fn key(&self, curve: u8) -> Result<Vec<u8>> {
      self.keys.get(curve).ok_or(Error::NonExistentCurve)
    }

    // TODO: voted
    // TODO: votes

    fn hash<T: Encode>(value: &T) -> [u8; 32] {
      let mut output = [0; 32];
      hash_encoded::<Blake2x256, _>(value, &mut output);
      output
    }

    /// Vote for a given set of keys.
    #[ink(message)]
    pub fn vote(&mut self, keys: Vec<Vec<u8>>) -> Result<()> {
      if keys.len() > 256 {
        Err(Error::NonExistentCurve)?;
      }

      let validator = self.env().caller();
      if !self.env().extension().is_active_validator(&validator) {
        Err(Error::NotValidator)?;
      }

      let validator_set = self.env().extension().validator_set_id();
      if self.validator_set == validator_set {
        Err(Error::AlreadyGeneratedKeys)?;
      }

      let keys_hash = Self::hash(&keys);
      if self.voted.get((validator, keys_hash)).is_some() {
        Err(Error::AlreadyVoted)?;
      }
      self.voted.insert((validator, keys_hash), &());

      let votes = if let Some(votes) = self.votes.get((validator_set, keys_hash)) {
        self.env().emit_event(Vote { validator, validator_set, hash: keys_hash, keys: None });
        votes + 1
      } else {
        self.env().emit_event(Vote {
          validator,
          validator_set,
          hash: keys_hash,
          keys: Some(keys.clone()),
        });
        1
      };
      // We could skip writing this if we've reached consensus, yet best to keep our ducks in a row
      self.votes.insert((validator_set, keys_hash), &votes);

      // If we've reached consensus, action this.
      if votes == self.env().extension().active_validators_len() {
        self.validator_set = validator_set;
        for (k, key) in keys.iter().enumerate() {
          self.keys.insert(u8::try_from(k).unwrap(), key);
        }
        self.env().emit_event(KeyGen { hash: keys_hash });
      }

      Ok(())
    }
  }

  #[cfg(test)]
  mod tests {
    use std::sync::Mutex;

    use lazy_static::lazy_static;

    use ink_env::{
      hash::{CryptoHash, Blake2x256},
      AccountId,
      topics::PrefixedValue,
    };
    use ink_lang as ink;

    use serai_extension::{test_validators, test_register};

    use super::*;

    type Event = <Multisig as ::ink_lang::reflect::ContractEventBase>::Type;

    lazy_static! {
      static ref keys: Vec<Vec<u8>> = vec![vec![0, 1], vec![2, 3]];
    }

    fn hash_prefixed<T: scale::Encode>(prefixed: PrefixedValue<T>) -> [u8; 32] {
      let encoded = prefixed.encode();
      let mut hash = [0; 32];
      if encoded.len() < 32 {
        hash[.. encoded.len()].copy_from_slice(&encoded);
      } else {
        Blake2x256::hash(&encoded, &mut hash);
      }
      hash
    }

    fn assert_vote(
      event: &ink_env::test::EmittedEvent,
      expected_validator: AccountId,
      expected_validator_set: [u8; 32],
      expected_keys: Option<()>,
    ) {
      let mut expected_hash = [0; 32];
      ink_env::hash_encoded::<Blake2x256, _>(&*keys, &mut expected_hash);

      let decoded_event = <Event as scale::Decode>::decode(&mut &event.data[..])
        .expect("encountered invalid contract event data buffer");

      if let Event::Vote(Vote { validator, validator_set, hash, keys: actual_keys }) = decoded_event
      {
        assert_eq!(validator, expected_validator);
        assert_eq!(validator_set, expected_validator_set);
        assert_eq!(hash, expected_hash);
        assert_eq!(actual_keys.as_ref(), expected_keys.map(|_| &*keys));
      } else {
        panic!("invalid Vote event")
      }

      let expected_topics = vec![
        hash_prefixed(PrefixedValue { prefix: b"", value: b"Multisig::Vote" }),
        hash_prefixed(PrefixedValue {
          prefix: b"Multisig::Vote::validator",
          value: &expected_validator,
        }),
        hash_prefixed(PrefixedValue {
          prefix: b"Multisig::Vote::validator_set",
          value: &expected_validator_set,
        }),
        hash_prefixed(PrefixedValue { prefix: b"Multisig::Vote::hash", value: &expected_hash }),
      ];

      for (n, (actual_topic, expected_topic)) in
        event.topics.iter().zip(expected_topics).enumerate()
      {
        assert_eq!(actual_topic, &expected_topic, "encountered invalid topic at {}", n);
      }
    }

    /// The default constructor does its job.
    #[ink::test]
    fn new() {
      let multisig = Multisig::new();
      assert_eq!(multisig.validator_set(), [0; 32]);
    }

    /// Non-existent curves error accordingly.
    #[ink::test]
    fn non_existent_curve() {
      assert_eq!(Multisig::new().key(0), Err(Error::NonExistentCurve));
    }

    #[ink::test]
    fn success() {
      test_register();
      let mut multisig = Multisig::new().try_lock().unwrap();

      /// Test voting on keys works without issue, emitting the keys for the first vote
      for (i, validator) in test_validators().iter().enumerate() {
        ink_env::test::set_caller::<ink_env::DefaultEnvironment>(test_validators()[i]);
        multisig.vote(keys.clone()).unwrap();

        let emitted_events = ink_env::test::recorded_events().collect::<Vec<_>>();
        assert_eq!(emitted_events.len(), i + 1);
        assert_vote(
          &emitted_events[i],
          AccountId::from([2; 32]),
          [0xff; 32],
          // Only the first event for this hash should have the keys
          Some(()).filter(|_| i == 0),
        );
      }
    }
  }
}

Absolutely not minimal, sorry, yet the relevant section is the doc comment on the for loop. This is not an ICE when I remove one of the slashes.

Meta

rustc --version --verbose:

rustc 1.64.0-nightly (c2f428d2f 2022-07-14)
binary: rustc
commit-hash: c2f428d2f3340a0e7d995f4726223db91b93704c
commit-date: 2022-07-14
host: x86_64-unknown-linux-gnu
release: 1.64.0-nightly
LLVM version: 14.0.6

Error output

warning: unused doc comment
   --> contracts/multisig/lib.rs:247:7
    |
247 |         /// Test voting on keys works without issue, emitting the keys for the first vote
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
248 | /       for (i, validator) in test_validators().iter().enumerate() {
249 | |         ink_env::test::set_caller::<ink_env::DefaultEnvironment>(test_validators()[i]);
250 | |         multisig.vote(keys.clone()).unwrap();
251 | |
...   |
260 | |         );
261 | |       }
    | |_______- rustdoc does not generate documentation for expressions
    |
    = note: `#[warn(unused_doc_comments)]` on by default
    = help: use `//` for a plain comment

thread 'rustc' panicked at 'internal error: entered unreachable code: in literal form when lowering mac args eq: Lit { token: Lit { kind: Str, symbol: " Test voting on keys works without issue, emitting the keys for the first vote", suffix: None }, kind: Str(" Test voting on keys works without issue, emitting the keys for the first vote", Cooked), span: contracts/multisig/lib.rs:247:7: 247:88 (#0) }', compiler/rustc_ast_lowering/src/lib.rs:914:17

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 1.64.0-nightly (c2f428d2f 2022-07-14) running on x86_64-unknown-linux-gnu

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

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

query stack during panic:
#0 [hir_crate] get the crate HIR
#1 [entry_fn] looking up the entry function of a crate
#2 [analysis] running analysis passes on this crate
end of query stack

Backtrace

``` stack backtrace: 0: 0x7fb68e4a2950 - std::backtrace_rs::backtrace::libunwind::trace::heeafe1f1ea6b4c2f at /rustc/c2f428d2f3340a0e7d995f4726223db91b93704c/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5 1: 0x7fb68e4a2950 - std::backtrace_rs::backtrace::trace_unsynchronized::hf08684e78cd6c167 at /rustc/c2f428d2f3340a0e7d995f4726223db91b93704c/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5 2: 0x7fb68e4a2950 - std::sys_common::backtrace::_print_fmt::had9e99c2c8763a1e at /rustc/c2f428d2f3340a0e7d995f4726223db91b93704c/library/std/src/sys_common/backtrace.rs:66:5 3: 0x7fb68e4a2950 - ::fmt::h1b4c432d2a1e6303 at /rustc/c2f428d2f3340a0e7d995f4726223db91b93704c/library/std/src/sys_common/backtrace.rs:45:22 4: 0x7fb68e4fbf2c - core::fmt::write::h87085de871a99231 at /rustc/c2f428d2f3340a0e7d995f4726223db91b93704c/library/core/src/fmt/mod.rs:1198:17 5: 0x7fb68e494015 - std::io::Write::write_fmt::h7635d2f423aa55dc at /rustc/c2f428d2f3340a0e7d995f4726223db91b93704c/library/std/src/io/mod.rs:1672:15 6: 0x7fb68e4a55e1 - std::sys_common::backtrace::_print::hc003bc1c22b7967b at /rustc/c2f428d2f3340a0e7d995f4726223db91b93704c/library/std/src/sys_common/backtrace.rs:48:5 7: 0x7fb68e4a55e1 - std::sys_common::backtrace::print::h1baa1ab7758e52b0 at /rustc/c2f428d2f3340a0e7d995f4726223db91b93704c/library/std/src/sys_common/backtrace.rs:35:9 8: 0x7fb68e4a55e1 - std::panicking::default_hook::{{closure}}::he2f5e84c6ab77817 at /rustc/c2f428d2f3340a0e7d995f4726223db91b93704c/library/std/src/panicking.rs:295:22 9: 0x7fb68e4a52b3 - std::panicking::default_hook::h3f96069db270c68f at /rustc/c2f428d2f3340a0e7d995f4726223db91b93704c/library/std/src/panicking.rs:314:9 10: 0x7fb68ed49de4 - rustc_driver[1ce26eb46f30f4d]::DEFAULT_HOOK::{closure#0}::{closure#0} 11: 0x7fb68e4a5db6 - std::panicking::rust_panic_with_hook::hed0c1597bbc695a6 at /rustc/c2f428d2f3340a0e7d995f4726223db91b93704c/library/std/src/panicking.rs:702:17 12: 0x7fb68e4a5c07 - std::panicking::begin_panic_handler::{{closure}}::h0fc9e6b3154da131 at /rustc/c2f428d2f3340a0e7d995f4726223db91b93704c/library/std/src/panicking.rs:588:13 13: 0x7fb68e4a2e34 - std::sys_common::backtrace::__rust_end_short_backtrace::hb9c2240a67931ff9 at /rustc/c2f428d2f3340a0e7d995f4726223db91b93704c/library/std/src/sys_common/backtrace.rs:138:18 14: 0x7fb68e4a5932 - rust_begin_unwind at /rustc/c2f428d2f3340a0e7d995f4726223db91b93704c/library/std/src/panicking.rs:584:5 15: 0x7fb68e469c33 - core::panicking::panic_fmt::h6bda1b0556b509cd at /rustc/c2f428d2f3340a0e7d995f4726223db91b93704c/library/core/src/panicking.rs:142:14 16: 0x7fb6902a91eb - as core[32c218dbf3427c26]::iter::traits::collect::Extend>::extend::, ::lower_attrs::{closure#0}>> 17: 0x7fb6902d1c1e - ::alloc_from_iter::, ::lower_attrs::{closure#0}>> 18: 0x7fb6902780e4 - ::expr 19: 0x7fb69111de78 - ::lower_expr_for 20: 0x7fb690271b64 - ::lower_expr_mut 21: 0x7fb69026d9fe - ::lower_block_noalloc 22: 0x7fb690270c1d - ::lower_expr_mut 23: 0x7fb69026d9fe - ::lower_block_noalloc 24: 0x7fb690270c1d - ::lower_expr_mut 25: 0x7fb69026e1d2 - ::lower_block_noalloc 26: 0x7fb690270c1d - ::lower_expr_mut 27: 0x7fb69026d9fe - ::lower_block_noalloc 28: 0x7fb690270c1d - ::lower_expr_mut 29: 0x7fb69111b5e1 - ::lower_expr_closure 30: 0x7fb69027170c - ::lower_expr_mut 31: 0x7fb69027044d - ::lower_expr_mut 32: 0x7fb690270770 - ::lower_expr_mut 33: 0x7fb69026dfa7 - ::lower_block_noalloc 34: 0x7fb69027f9d4 - ::lower_maybe_async_body 35: 0x7fb6902797fa - ::lower_item_kind 36: 0x7fb69029bb59 - ::with_hir_id_owner::<::with_lctx<::lower_item::{closure#0}>::{closure#0}> 37: 0x7fb6902acffd - ::lower_node 38: 0x7fb690289278 - rustc_ast_lowering[3f3b0ef9be439d1a]::lower_to_hir 39: 0x7fb691413bec - >::with_task:: 40: 0x7fb69147ef02 - rustc_query_system[688aca7ce0d190ff]::query::plumbing::try_execute_query::> 41: 0x7fb68f75a12f - rustc_query_system[688aca7ce0d190ff]::query::plumbing::force_query:: 42: 0x7fb68f7367a6 - rustc_query_impl[e840a35d18f93fd8]::query_callbacks::hir_crate::force_from_dep_node 43: 0x7fb690ddf7f1 - ::try_force_from_dep_node 44: 0x7fb69088b316 - >::try_mark_previous_green:: 45: 0x7fb69088ab96 - >::try_mark_previous_green:: 46: 0x7fb69088a420 - >::try_mark_green:: 47: 0x7fb6914d8cbc - rustc_query_system[688aca7ce0d190ff]::query::plumbing::try_load_from_disk_and_cache_in_memory::> 48: 0x7fb6914ac124 - rustc_query_system[688aca7ce0d190ff]::query::plumbing::try_execute_query::>> 49: 0x7fb69150a9c0 - rustc_query_system[688aca7ce0d190ff]::query::plumbing::get_query:: 50: 0x7fb6914564d2 - ::entry_fn 51: 0x7fb690f5608d - ::time::, rustc_interface[694c7ab70a1d38bc]::passes::analysis::{closure#0}::{closure#0}::{closure#0}> 52: 0x7fb690f59a60 - ::time::<(), rustc_interface[694c7ab70a1d38bc]::passes::analysis::{closure#0}> 53: 0x7fb690f44e4e - rustc_interface[694c7ab70a1d38bc]::passes::analysis 54: 0x7fb69141206c - >::with_task::> 55: 0x7fb6914acd1b - rustc_query_system[688aca7ce0d190ff]::query::plumbing::try_execute_query::>> 56: 0x7fb69150a74e - rustc_query_system[688aca7ce0d190ff]::query::plumbing::get_query:: 57: 0x7fb690f2841e - ::enter::> 58: 0x7fb690f0c09e - ::enter::, rustc_errors[3b3e5bcd1e9c2834]::ErrorGuaranteed>> 59: 0x7fb690f081ff - rustc_span[717885ec7c6cd182]::with_source_map::, rustc_interface[694c7ab70a1d38bc]::interface::create_compiler_and_run, rustc_driver[1ce26eb46f30f4d]::run_compiler::{closure#1}>::{closure#1}> 60: 0x7fb690f244b0 - rustc_interface[694c7ab70a1d38bc]::interface::create_compiler_and_run::, rustc_driver[1ce26eb46f30f4d]::run_compiler::{closure#1}> 61: 0x7fb690f385b2 - >::set::, rustc_driver[1ce26eb46f30f4d]::run_compiler::{closure#1}>::{closure#0}, core[32c218dbf3427c26]::result::Result<(), rustc_errors[3b3e5bcd1e9c2834]::ErrorGuaranteed>> 62: 0x7fb690f0a78f - std[167b23ae759531ff]::sys_common::backtrace::__rust_begin_short_backtrace::, rustc_driver[1ce26eb46f30f4d]::run_compiler::{closure#1}>::{closure#0}, core[32c218dbf3427c26]::result::Result<(), rustc_errors[3b3e5bcd1e9c2834]::ErrorGuaranteed>>::{closure#0}, core[32c218dbf3427c26]::result::Result<(), rustc_errors[3b3e5bcd1e9c2834]::ErrorGuaranteed>> 63: 0x7fb690f24909 - <::spawn_unchecked_, rustc_driver[1ce26eb46f30f4d]::run_compiler::{closure#1}>::{closure#0}, core[32c218dbf3427c26]::result::Result<(), rustc_errors[3b3e5bcd1e9c2834]::ErrorGuaranteed>>::{closure#0}, core[32c218dbf3427c26]::result::Result<(), rustc_errors[3b3e5bcd1e9c2834]::ErrorGuaranteed>>::{closure#1} as core[32c218dbf3427c26]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0} 64: 0x7fb68e4af803 - as core::ops::function::FnOnce>::call_once::h86b1834fb0da834b at /rustc/c2f428d2f3340a0e7d995f4726223db91b93704c/library/alloc/src/boxed.rs:1934:9 65: 0x7fb68e4af803 - as core::ops::function::FnOnce>::call_once::h124d05192aaf60e0 at /rustc/c2f428d2f3340a0e7d995f4726223db91b93704c/library/alloc/src/boxed.rs:1934:9 66: 0x7fb68e4af803 - std::sys::unix::thread::Thread::new::thread_start::h01e8d05fb6e030ea at /rustc/c2f428d2f3340a0e7d995f4726223db91b93704c/library/std/src/sys/unix/thread.rs:108:17 67: 0x7fb68e08c54d - 68: 0x7fb68e111874 - clone 69: 0x0 - ```

[jieyouxu]

Hi @kayabaNerve is this still an issue on latest stable/nightly?