'called `Option::unwrap()` on a `None` value' when editing KAS GUI applications

[nyanpasu64]

When I clone kas (https://github.com/kas-gui/kas) and open an example file, every edit or lookup triggers a rust-analyzer panic:

Output log and stack trace

Panic context:
> 
version: 009e6ceb1 2021-09-27 stable
request: textDocument/semanticTokens/full/delta SemanticTokensDeltaParams {
    work_done_progress_params: WorkDoneProgressParams {
        work_done_token: None,
    },
    partial_result_params: PartialResultParams {
        partial_result_token: None,
    },
    text_document: TextDocumentIdentifier {
        uri: Url {
            scheme: "file",
            cannot_be_a_base: false,
            username: "",
            password: None,
            host: None,
            port: None,
            path: "/home/nyanpasu64/code/kas/examples/counter.rs",
            query: None,
            fragment: None,
        },
    },
    previous_result_id: "2",
}

thread '<unnamed>' panicked at 'called `Option::unwrap()` on a `None` value', /home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/salsa-0.17.0-pre.1/src/runtime.rs:324:18
stack backtrace:
   0: rust_begin_unwind
             at /rustc/c8dfcfe046a7680554bf4eb612bad840e7631c4b/library/std/src/panicking.rs:515:5
   1: core::panicking::panic_fmt
             at /rustc/c8dfcfe046a7680554bf4eb612bad840e7631c4b/library/core/src/panicking.rs:92:14
   2: core::panicking::panic
             at /rustc/c8dfcfe046a7680554bf4eb612bad840e7631c4b/library/core/src/panicking.rs:50:5
   3: salsa::runtime::Runtime::report_unexpected_cycle
   4: salsa::derived::slot::Slot<Q,MP>::read
   5: <salsa::derived::DerivedStorage<Q,MP> as salsa::plumbing::QueryStorageOps<Q>>::try_fetch
   6: <DB as hir_ty::db::HirDatabase>::generic_predicates_for_param
   7: hir_ty::lower::TyLoweringContext::lower_ty_relative_path
   8: hir_ty::lower::TyLoweringContext::lower_partly_resolved_path
   9: hir_ty::lower::TyLoweringContext::lower_ty_ext
  10: hir_ty::lower::TyLoweringContext::substs_from_path_segment
  11: hir_ty::lower::TyLoweringContext::lower_trait_ref_from_path
  12: hir_ty::lower::TyLoweringContext::lower_type_bound
  13: hir_ty::lower::TyLoweringContext::lower_where_predicate
  14: <core::iter::adapters::flatten::FlatMap<I,U,F> as core::iter::traits::iterator::Iterator>::next
  15: <alloc::vec::Vec<T> as alloc::vec::spec_from_iter::SpecFromIter<T,I>>::from_iter
  16: hir_ty::lower::generic_predicates_for_param_query
  17: salsa::runtime::Runtime::execute_query_implementation
  18: salsa::derived::slot::Slot<Q,MP>::read_upgrade
  19: salsa::derived::slot::Slot<Q,MP>::maybe_changed_since
  20: <salsa::derived::DerivedStorage<Q,MP> as salsa::plumbing::QueryStorageOps<Q>>::maybe_changed_since
  21: salsa::derived::slot::MemoRevisions::validate_memoized_value
  22: salsa::derived::slot::Slot<Q,MP>::read_upgrade
  23: salsa::derived::slot::Slot<Q,MP>::maybe_changed_since
  24: <salsa::derived::DerivedStorage<Q,MP> as salsa::plumbing::QueryStorageOps<Q>>::maybe_changed_since
  25: salsa::derived::slot::MemoRevisions::validate_memoized_value
  26: salsa::derived::slot::Slot<Q,MP>::read_upgrade
  27: salsa::derived::slot::Slot<Q,MP>::maybe_changed_since
  28: <salsa::derived::DerivedStorage<Q,MP> as salsa::plumbing::QueryStorageOps<Q>>::maybe_changed_since
  29: salsa::derived::slot::MemoRevisions::validate_memoized_value
  30: salsa::derived::slot::Slot<Q,MP>::read_upgrade
  31: salsa::derived::slot::Slot<Q,MP>::maybe_changed_since
  32: <salsa::derived::DerivedStorage<Q,MP> as salsa::plumbing::QueryStorageOps<Q>>::maybe_changed_since
  33: salsa::derived::slot::MemoRevisions::validate_memoized_value
  34: salsa::derived::slot::Slot<Q,MP>::read_upgrade
  35: salsa::derived::slot::Slot<Q,MP>::maybe_changed_since
  36: <salsa::derived::DerivedStorage<Q,MP> as salsa::plumbing::QueryStorageOps<Q>>::maybe_changed_since
  37: salsa::derived::slot::MemoRevisions::validate_memoized_value
  38: salsa::derived::slot::Slot<Q,MP>::read_upgrade
  39: salsa::derived::slot::Slot<Q,MP>::read
  40: <salsa::derived::DerivedStorage<Q,MP> as salsa::plumbing::QueryStorageOps<Q>>::try_fetch
  41: <DB as hir_ty::db::HirDatabase>::infer_query
  42: hir_ty::db::infer_wait
  43: hir::source_analyzer::SourceAnalyzer::new_for_body
  44: hir::semantics::SemanticsImpl::analyze_impl
  45: ide_db::defs::NameClass::classify
  46: ide::syntax_highlighting::highlight::element
  47: ide::syntax_highlighting::traverse
  48: ide::syntax_highlighting::highlight
  49: std::panicking::try
  50: rust_analyzer::handlers::handle_semantic_tokens_full_delta
  51: std::panicking::try
  52: <F as threadpool::FnBox>::call_box
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
[Error - 12:41:02 AM] Request textDocument/semanticTokens/full/delta failed.
  Message: server panicked: called `Option::unwrap()` on a `None` value
  Code: -32603 

I think this is related to #5001. I think kas is valid code, but I'm getting report_unexpected_cycle crashes anyway.

The error goes away when I disable rust-analyzer.procMacro.enable or remove all methods from the make_widget! { impl { block.

Currently on vscode 1.60.2 and rust-analyzer extension v0.2.760 (both latest I think).
rust-analyzer version: 009e6ce 2021-09-27 stable

Is there anything that needs to be done to expand macros or minify the test case?

[lnicola]

Can you try with a nightly? I was able to reproduce it before (but not after) #10353, and there was also #10305 touching that code.

CC @SkiFire13 just in case.

Unfortunately, I did get this after #10305:

thread '<unnamed>' panicked at 'index out of bounds: the len is 0 but the index is 0', ~/.cargo/registry/src/github.com-1ecc6299db9ec823/chalk-ir-0.71.0/src/lib.rs:2752:10
stack backtrace:
   0: rust_begin_unwind
             at /rustc/c8dfcfe046a7680554bf4eb612bad840e7631c4b/library/std/src/panicking.rs:515:5
   1: core::panicking::panic_fmt
             at /rustc/c8dfcfe046a7680554bf4eb612bad840e7631c4b/library/core/src/panicking.rs:92:14
   2: core::panicking::panic_bounds_check
             at /rustc/c8dfcfe046a7680554bf4eb612bad840e7631c4b/library/core/src/panicking.rs:69:5
   3: <&chalk_ir::SubstFolder<I,A> as chalk_ir::fold::Folder<I>>::fold_free_var_ty
   4: <chalk_ir::Ty<I> as chalk_ir::fold::SuperFold<I>>::super_fold_with
   5: chalk_ir::fold::boring_impls::<impl chalk_ir::fold::Fold<I> for chalk_ir::GenericArg<I>>::fold_with
   6: <smallvec::SmallVec<A> as core::iter::traits::collect::Extend<<A as smallvec::Array>::Item>>::extend
   7: chalk_ir::fold::boring_impls::<impl chalk_ir::fold::Fold<I> for chalk_ir::Substitution<I>>::fold_with
   8: <chalk_ir::Ty<I> as chalk_ir::fold::SuperFold<I>>::super_fold_with
   9: chalk_ir::fold::boring_impls::<impl chalk_ir::fold::Fold<I> for chalk_ir::GenericArg<I>>::fold_with
  10: <smallvec::SmallVec<A> as core::iter::traits::collect::Extend<<A as smallvec::Array>::Item>>::extend
  11: chalk_ir::fold::boring_impls::<impl chalk_ir::fold::Fold<I> for chalk_ir::Substitution<I>>::fold_with
  12: chalk_ir::_::<impl chalk_ir::fold::Fold<I> for chalk_ir::WhereClause<I>>::fold_with
  13: chalk_ir::_::<impl chalk_ir::fold::Fold<I> for chalk_ir::DomainGoal<I>>::fold_with
  14: chalk_ir::_::<impl chalk_ir::fold::Fold<_I> for chalk_ir::InEnvironment<G>>::fold_with
  15: chalk_solve::infer::InferenceTable<I>::from_canonical
  16: chalk_recursive::solve::SolveIteration::solve_iteration
  17: chalk_recursive::fixed_point::RecursiveContext<K,V>::solve_goal
  18: chalk_recursive::fixed_point::RecursiveContext<K,V>::solve_root_goal
  19: hir_ty::traits::trait_solve_query
  20: salsa::runtime::Runtime::execute_query_implementation
  21: salsa::derived::slot::Slot<Q,MP>::read_upgrade
  22: salsa::derived::slot::Slot<Q,MP>::read
  23: <salsa::derived::DerivedStorage<Q,MP> as salsa::plumbing::QueryStorageOps<Q>>::try_fetch
  24: <DB as hir_ty::db::HirDatabase>::trait_solve_query::__shim
  25: <DB as hir_ty::db::HirDatabase>::trait_solve_query
  26: hir_ty::db::trait_solve_wait
  27: <DB as hir_ty::db::HirDatabase>::trait_solve
  28: hir_ty::autoderef::deref_by_trait
  29: hir_ty::autoderef::deref
  30: <core::iter::adapters::map::Map<I,F> as core::iter::traits::iterator::Iterator>::fold
  31: <hashbrown::map::HashMap<K,V,S,A> as core::iter::traits::collect::Extend<(K,V)>>::extend
  32: ide_db::helpers::import_assets::trait_applicable_items
  33: ide_db::helpers::import_assets::ImportAssets::search_for
  34: ide_db::helpers::import_assets::ImportAssets::search_for_imports
  35: ide_completion::completions::flyimport::import_on_the_fly
  36: ide_completion::completions
  37: std::panicking::try
  38: ide::Analysis::completions
  39: rust_analyzer::handlers::handle_completion
  40: std::panicking::try
  41: <F as threadpool::FnBox>::call_box
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
  103ms - handle_completion
        0   - Semantics::analyze_impl (7 calls)
        3ms - SourceBinder::to_module_def (3 calls)
        0   - crate_def_map:wait (22 calls)
       37ms - descend_into_macros (1 calls)
       12ms - import_on_the_fly (1 calls)
       32ms - iterate_path_candidates (1 calls)
[Error - 13:03:17] Request textDocument/completion failed.
  Message: server panicked: index out of bounds: the len is 0 but the index is 0
  Code: -32603

[dhardy]

The file in question: examples/counter.rs.

Using:

$ rls --version
rls 1.41.0 (a82a052 2021-07-21)
$ kate --version
kate 21.08.0

I don't see this error myself, and the RLS plugin is able to report errors within the macro as well as link some of the symbols (Label<String> and VoidMsg) but not others (row!, TextButton and handle_button, the latter not being at all surprising since linkage is defined by the macro).

[lnicola]

RLS and rust-analyzer are quite unrelated, and I'd generally expect RLS to be more precise when it works.

For the record, I checked in with the calculator example. I got that crash when editing the code inside the make_widget call.

[jonas-schievink]

The salsa bug is salsa-rs/salsa#257

[SkiFire13]

Can you try with a nightly? I was able to reproduce it before (but not after) #10353, and there was also #10305 touching that code.

CC @SkiFire13 just in case.

Unfortunately, I did get this after #10305:

For the record, I checked in with the calculator example. I got that crash when editing the code inside the make_widget call.

Unfortunately I'm not able to reproduce this. Both nightly and a local-built version seem to not trigger even the salsa panic with the calculator example. They still trigger it with the counter example, but it's not the chalk one.

[nyanpasu64]

I've created a minimal test case (place this at "examples/counter-expand.rs"):

use std::marker::PhantomData;

struct AnonWidget<T: kas::Widget> {
    buttons: PhantomData<T>,
}

impl<T: kas::Widget> AnonWidget<T> {
    // removing &self stops crashes
    fn fmt(&self) {
        // type something and press ctrl+space on a new line to trigger panic

    }
}

fn main() {}

This doesn't crash on every keystroke like before, but if you place the cursor on the blank line, then repeatedly type some gibberish and trigger autocomplete, within a few cycles you should get rust-analyzer to start panicking (even if you disable proc macros).

rust.analyzer.kas.panic.mp4

Output log and stack trace:

Panic context:
> 
version: 009e6ceb1 2021-09-27 stable
request: textDocument/completion CompletionParams {
    text_document_position: TextDocumentPositionParams {
        text_document: TextDocumentIdentifier {
            uri: Url {
                scheme: "file",
                cannot_be_a_base: false,
                username: "",
                password: None,
                host: None,
                port: None,
                path: "/home/nyanpasu64/code/kas/examples/counter-expand.rs",
                query: None,
                fragment: None,
            },
        },
        position: Position {
            line: 10,
            character: 9,
        },
    },
    work_done_progress_params: WorkDoneProgressParams {
        work_done_token: None,
    },
    partial_result_params: PartialResultParams {
        partial_result_token: None,
    },
    context: Some(
        CompletionContext {
            trigger_kind: Invoked,
            trigger_character: None,
        },
    ),
}

thread '<unnamed>' panicked at 'called `Option::unwrap()` on a `None` value', /home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/salsa-0.17.0-pre.1/src/runtime.rs:324:18
stack backtrace:
   0: rust_begin_unwind
             at /rustc/c8dfcfe046a7680554bf4eb612bad840e7631c4b/library/std/src/panicking.rs:515:5
   1: core::panicking::panic_fmt
             at /rustc/c8dfcfe046a7680554bf4eb612bad840e7631c4b/library/core/src/panicking.rs:92:14
   2: core::panicking::panic
             at /rustc/c8dfcfe046a7680554bf4eb612bad840e7631c4b/library/core/src/panicking.rs:50:5
   3: salsa::runtime::Runtime::report_unexpected_cycle
   4: salsa::derived::slot::Slot<Q,MP>::read
   5: <salsa::derived::DerivedStorage<Q,MP> as salsa::plumbing::QueryStorageOps<Q>>::try_fetch
   6: <DB as hir_ty::db::HirDatabase>::generic_predicates_for_param
   7: hir_ty::lower::TyLoweringContext::lower_ty_relative_path
   8: hir_ty::lower::TyLoweringContext::lower_partly_resolved_path
   9: hir_ty::lower::TyLoweringContext::lower_ty_ext
  10: hir_ty::lower::TyLoweringContext::substs_from_path_segment
  11: hir_ty::lower::TyLoweringContext::lower_trait_ref_from_path
  12: hir_ty::lower::TyLoweringContext::lower_type_bound
  13: hir_ty::lower::TyLoweringContext::lower_where_predicate
  14: <core::iter::adapters::flatten::FlatMap<I,U,F> as core::iter::traits::iterator::Iterator>::next
  15: <alloc::vec::Vec<T> as alloc::vec::spec_from_iter::SpecFromIter<T,I>>::from_iter
  16: hir_ty::lower::generic_predicates_for_param_query
  17: salsa::runtime::Runtime::execute_query_implementation
  18: salsa::derived::slot::Slot<Q,MP>::read_upgrade
  19: salsa::derived::slot::Slot<Q,MP>::maybe_changed_since
  20: <salsa::derived::DerivedStorage<Q,MP> as salsa::plumbing::QueryStorageOps<Q>>::maybe_changed_since
  21: salsa::derived::slot::MemoRevisions::validate_memoized_value
  22: salsa::derived::slot::Slot<Q,MP>::read_upgrade
  23: salsa::derived::slot::Slot<Q,MP>::maybe_changed_since
  24: <salsa::derived::DerivedStorage<Q,MP> as salsa::plumbing::QueryStorageOps<Q>>::maybe_changed_since
  25: salsa::derived::slot::MemoRevisions::validate_memoized_value
  26: salsa::derived::slot::Slot<Q,MP>::read_upgrade
  27: salsa::derived::slot::Slot<Q,MP>::maybe_changed_since
  28: <salsa::derived::DerivedStorage<Q,MP> as salsa::plumbing::QueryStorageOps<Q>>::maybe_changed_since
  29: salsa::derived::slot::MemoRevisions::validate_memoized_value
  30: salsa::derived::slot::Slot<Q,MP>::read_upgrade
  31: salsa::derived::slot::Slot<Q,MP>::maybe_changed_since
  32: <salsa::derived::DerivedStorage<Q,MP> as salsa::plumbing::QueryStorageOps<Q>>::maybe_changed_since
  33: salsa::derived::slot::MemoRevisions::validate_memoized_value
  34: salsa::derived::slot::Slot<Q,MP>::read_upgrade
  35: salsa::derived::slot::Slot<Q,MP>::read
  36: <salsa::derived::DerivedStorage<Q,MP> as salsa::plumbing::QueryStorageOps<Q>>::try_fetch
  37: <DB as hir_ty::db::HirDatabase>::trait_solve_query::__shim
  38: <DB as hir_ty::db::HirDatabase>::trait_solve_query
  39: hir_ty::db::trait_solve_wait
  40: <DB as hir_ty::db::HirDatabase>::trait_solve
  41: hir_ty::method_resolution::iterate_trait_method_candidates
  42: hir_ty::method_resolution::iterate_method_candidates_by_receiver
  43: hir_ty::method_resolution::iterate_method_candidates_dyn
  44: hir::Type::iterate_method_candidates_dyn
  45: hir::Type::iterate_method_candidates
  46: ide_completion::completions::dot::complete_undotted_self::{{closure}}
  47: hir::semantics::SemanticsScope::process_all_names
  48: ide_completion::completions::dot::complete_dot
  49: ide_completion::completions
  50: std::panicking::try
  51: rust_analyzer::handlers::handle_completion
  52: std::panicking::try
  53: <F as threadpool::FnBox>::call_box
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
[Error - 1:46:13 PM] Request textDocument/completion failed.
  Message: server panicked: called `Option::unwrap()` on a `None` value
  Code: -32603 

The interesting thing I noticed is that kas::Widget is a child of an absurdly long chain of trait single inheritance, ending with pub trait WidgetCore: Any + fmt::Debug. If necessary, I can try to further minimize this by removing the dependence on kas::Widget.

I also get a Salsa crash on "rust-analyzer version: 533ca58 2021-09-28 nightly" (output log and stack trace).

[tmandry]

Unfortunately, I did get this after #10305:

Me too. Filed #10390 for this.

[nyanpasu64]

The full chain of traits is:

• kas::Widget
• kas::event::SendEvent
• kas::event::Handler
• kas::WidgetConfig
• kas::Layout
• kas::WidgetChildren
• kas::WidgetCore
• Any + Debug

with some of these traits being re-exports.

I found that all child traits including kas::event::Handler crash, while all parent traits not including it do not crash. And that pub trait Handler { type Msg: 'static; } is sufficient to induce the crash.

This should be a highly minimal test case. It crashes on completion, including when I restart rust-analyzer or vscode. Unfortunately, I can't reproduce the crash when I move Handler into the same file, either inline with AnonWidget or in a child module.

Is there some local state in my target directory or elsewhere, which could "prime" rust-analyzer to break on certain types, when it wouldn't break on a fresh clone? I haven't tested reproducing this on a fresh clone, but I'm working under the assumption that rust-analyzer has no memory saved across restarts, and this crash isn't related to cached state.

---

Sometimes clearing out my code stops the crashes, sometimes rust-analyzer even crashes on an empty file and I have to restart RA or vscode to stop the panics.

I found that switching Handler to pub trait Handler { type Msg2: 'static; } still reproduces the crash, but renaming Handler (in event/handler.rs and/or event/mod.rs) stops the crash. I suspect the crash is caused by the usages of this trait (impl Handler for T or impl Trait for Handler), not the trait itself.

[nyanpasu64]

I found that stubbing out the entire kas-widgets crate fixed the crash. While searching through kas-widgets, I found my stripped-down version of mod single_view's struct SingleView was necessary and sufficient to reproduce the crash, if most other modules were stubbed out (kas_widgets was reduced to pub mod view; and kas_widgets::view was reduced to pub mod single_view; pub mod driver; pub use driver::Driver;). I can upload my cut-down git repository if needed. (There may be other sources for similar crashes, which I have not tried to identify.)

https://github.com/kas-gui/kas/blob/986d013171aa92741b03d64696b83d8bd91daaf4/crates/kas-widgets/src/view/single_view.rs#L30-L33

struct SingleView has 2 type parameters, each with a trait bound constrained by the other type parameter's associated type. This is consistent with the original crash message mentioning report_unexpected_cycle.

Note that T::Item is defined in SingleData and not UpdHandler, so in one sense it's not a cycle. rust-analyzer crashes whether I include SingleData or not in the trait list. I don't know if this code should be valid or not, but I think it compiles fine in rustc.

EDIT: Even in source files where there's truly a cycle, salsa should report an error and not panic.

[lnicola]

This doesn't crash on every keystroke like before, but if you place the cursor on the blank line, then repeatedly type some gibberish and trigger autocomplete, within a few cycles you should get rust-analyzer to start panicking (even if you disable proc macros).

Okay, it looks a bit different from yours but I still get a panic on b21f15a23767c8d06ab5da60f59b8b197c45831a with that test case:

thread '<unnamed>' panicked at 'called `Option::unwrap()` on a `None` value', ~/.cargo/registry/src/github.com-1ecc6299db9ec823/salsa-0.17.0-pre.1/src/runtime.rs:324:18
stack backtrace:
   0: rust_begin_unwind
             at /rustc/c8dfcfe046a7680554bf4eb612bad840e7631c4b/library/std/src/panicking.rs:515:5
   1: core::panicking::panic_fmt
             at /rustc/c8dfcfe046a7680554bf4eb612bad840e7631c4b/library/core/src/panicking.rs:92:14
   2: core::panicking::panic
             at /rustc/c8dfcfe046a7680554bf4eb612bad840e7631c4b/library/core/src/panicking.rs:50:5
   3: salsa::runtime::Runtime::report_unexpected_cycle
   4: salsa::derived::slot::Slot<Q,MP>::read
   5: <salsa::derived::DerivedStorage<Q,MP> as salsa::plumbing::QueryStorageOps<Q>>::try_fetch
   6: <DB as hir_ty::db::HirDatabase>::generic_predicates_for_param::__shim
   7: hir_ty::lower::associated_type_shorthand_candidates
   8: hir_ty::lower::TyLoweringContext::lower_ty_relative_path
   9: hir_ty::lower::TyLoweringContext::lower_partly_resolved_path
  10: hir_ty::lower::TyLoweringContext::lower_ty_ext
  11: hir_ty::lower::TyLoweringContext::substs_from_path_segment
  12: hir_ty::lower::TyLoweringContext::lower_trait_ref_from_path
  13: hir_ty::lower::TyLoweringContext::lower_type_bound
  14: hir_ty::lower::TyLoweringContext::lower_where_predicate
  15: <core::iter::adapters::flatten::FlatMap<I,U,F> as core::iter::traits::iterator::Iterator>::next
  16: <alloc::vec::Vec<T> as alloc::vec::spec_from_iter::SpecFromIter<T,I>>::from_iter
  17: hir_ty::lower::generic_predicates_for_param_query
  18: salsa::runtime::Runtime::execute_query_implementation
  19: salsa::derived::slot::Slot<Q,MP>::read_upgrade
  20: salsa::derived::slot::Slot<Q,MP>::maybe_changed_since
  21: <salsa::derived::DerivedStorage<Q,MP> as salsa::plumbing::QueryStorageOps<Q>>::maybe_changed_since
  22: salsa::derived::slot::MemoRevisions::validate_memoized_value
  23: salsa::derived::slot::Slot<Q,MP>::read_upgrade
  24: salsa::derived::slot::Slot<Q,MP>::maybe_changed_since
  25: <salsa::derived::DerivedStorage<Q,MP> as salsa::plumbing::QueryStorageOps<Q>>::maybe_changed_since
  26: salsa::derived::slot::MemoRevisions::validate_memoized_value
  27: salsa::derived::slot::Slot<Q,MP>::read_upgrade
  28: salsa::derived::slot::Slot<Q,MP>::maybe_changed_since
  29: <salsa::derived::DerivedStorage<Q,MP> as salsa::plumbing::QueryStorageOps<Q>>::maybe_changed_since
  30: salsa::derived::slot::MemoRevisions::validate_memoized_value
  31: salsa::derived::slot::Slot<Q,MP>::read_upgrade
  32: salsa::derived::slot::Slot<Q,MP>::maybe_changed_since
  33: <salsa::derived::DerivedStorage<Q,MP> as salsa::plumbing::QueryStorageOps<Q>>::maybe_changed_since
  34: salsa::derived::slot::MemoRevisions::validate_memoized_value
  35: salsa::derived::slot::Slot<Q,MP>::read_upgrade
  36: salsa::derived::slot::Slot<Q,MP>::read
  37: <salsa::derived::DerivedStorage<Q,MP> as salsa::plumbing::QueryStorageOps<Q>>::try_fetch
  38: <DB as hir_ty::db::HirDatabase>::trait_solve_query::__shim
  39: <DB as hir_ty::db::HirDatabase>::trait_solve_query
  40: hir_ty::db::trait_solve_wait
  41: <DB as hir_ty::db::HirDatabase>::trait_solve
  42: hir_ty::method_resolution::iterate_trait_method_candidates
  43: hir_ty::method_resolution::iterate_method_candidates_by_receiver
  44: hir_ty::method_resolution::iterate_method_candidates_dyn
  45: hir::Type::iterate_method_candidates_dyn
  46: hir::Type::iterate_method_candidates
  47: ide_completion::completions::dot::complete_methods
  48: ide_completion::completions::dot::complete_undotted_self::{{closure}}
  49: hir::semantics::SemanticsScope::process_all_names
  50: ide_completion::completions::dot::complete_dot
  51: ide_completion::completions
  52: std::panicking::try
  53: ide::Analysis::completions
  54: rust_analyzer::handlers::handle_completion
  55: std::panicking::try
  56: <F as threadpool::FnBox>::call_box

---

By the way, what version are you on?

I also get a Salsa crash on "rust-analyzer version: 533ca58 2021-09-28 nightly" (output log and stack trace).

But in your log there's:

version: 009e6ceb1 2021-09-27 stable