Index out of bounds panic on "Find all references"

[charlespierce]

On some elements in my code base, running "Find all references" causes a panic with the following message:

Panic context:
> 
version: d15f646ff 2021-08-30 stable
request: textDocument/references ReferenceParams {
    text_document_position: TextDocumentPositionParams {
        text_document: TextDocumentIdentifier {
            uri: Url {
                scheme: "file",
                cannot_be_a_base: false,
                username: "",
                password: None,
                host: None,
                port: None,
                path: "redacted.rs",
                query: None,
                fragment: None,
            },
        },
        position: Position {
            line: 368,
            character: 21,
        },
    },
    work_done_progress_params: WorkDoneProgressParams {
        work_done_token: None,
    },
    partial_result_params: PartialResultParams {
        partial_result_token: None,
    },
    context: ReferenceContext {
        include_declaration: true,
    },
}

thread '<unnamed>' panicked at 'index out of bounds: the len is 1 but the index is 1', /Users/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/chalk-ir-0.70.0/src/lib.rs:2752:10
stack backtrace:
   0: _rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::panicking::panic_bounds_check
   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::Ty<I> as chalk_ir::fold::SuperFold<I>>::super_fold_with
   6: <chalk_ir::Ty<I> as chalk_ir::fold::SuperFold<I>>::super_fold_with
   7: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_method_call
   8: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
   9: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::check_call_arguments
  10: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
  11: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_coerce
  12: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_block
  13: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
  14: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_coerce
  15: hir_ty::infer::infer_query
  16: salsa::runtime::Runtime::execute_query_implementation
  17: salsa::derived::slot::Slot<Q,MP>::read_upgrade
  18: salsa::derived::slot::Slot<Q,MP>::read
  19: <salsa::derived::DerivedStorage<Q,MP> as salsa::plumbing::QueryStorageOps<Q>>::try_fetch
  20: <DB as hir_ty::db::HirDatabase>::infer_query
  21: hir_ty::db::infer_wait
  22: hir::source_analyzer::SourceAnalyzer::new_for_body
  23: hir::semantics::SemanticsImpl::analyze_impl
  24: hir::semantics::SemanticsImpl::descend_into_macros
  25: rowan::utility_types::TokenAtOffset<T>::map
  26: ide_db::search::FindUsages::search
  27: ide::references::find_all_refs
  28: std::panicking::try
  29: rust_analyzer::handlers::handle_references
  30: rust_analyzer::dispatch::RequestDispatcher::on::{{closure}}::{{closure}}
  31: <F as threadpool::FnBox>::call_box
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
[Error - 1:14:23 PM] Request textDocument/references failed.
  Message: server panicked: index out of bounds: the len is 1 but the index is 1
  Code: -32603 

Unfortunately, this is a fairly complicated internal project, so I can't find a minimal reproduction or share the code itself 🙁 That said, one thing I noticed is that this works on an older version of R-A (0.2.702), but started failing on the release after that.

[ghost]

same bug on find-references request

[charlespierce]

If it helps to triage, I just did a git bisect between the two versions and it looks like this commit is where the behavior changes: e89ad9f

Note: The failure mode in that commit appears to be an infinite hang, rather than a panic that gets reported, in later commits it becomes a panic that shows a message.

[maxbrunsfeld]

I'm seeing a similar stack trace, but while editing, instead of while running "find all references".

thread '<unnamed>' panicked at 'index out of bounds: the len is 1 but the index is 1', /Users/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/chalk-ir-0.70.0/src/lib.rs:2752:10
stack backtrace:
   0: _rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::panicking::panic_bounds_check
   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::Ty<I> as chalk_ir::fold::SuperFold<I>>::super_fold_with
   6: <chalk_ir::Ty<I> as chalk_ir::fold::SuperFold<I>>::super_fold_with
   7: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_method_call
   8: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
   9: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_coerce
  10: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_block
  11: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
  12: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr
  13: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
  14: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr
  15: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_block
  16: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
  17: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_coerce
  18: hir_ty::infer::infer_query
  19: salsa::runtime::Runtime::execute_query_implementation
  20: salsa::derived::slot::Slot<Q,MP>::read_upgrade
  21: salsa::derived::slot::Slot<Q,MP>::read
  22: <salsa::derived::DerivedStorage<Q,MP> as salsa::plumbing::QueryStorageOps<Q>>::try_fetch
  23: <DB as hir_ty::db::HirDatabase>::infer_query
  24: hir_ty::db::infer_wait
  25: hir::DefWithBody::diagnostics
  26: hir::Module::diagnostics
  27: ide_diagnostics::diagnostics
  28: ide::Analysis::assists_with_fixes::{{closure}}
  29: std::panicking::try
  30: rust_analyzer::handlers::handle_code_action
  31: rust_analyzer::dispatch::RequestDispatcher::on::{{closure}}::{{closure}}
  32: <F as threadpool::FnBox>::call_box

[maxbrunsfeld]

If it helps to triage, I just did a git bisect between the two versions and it looks like this commit is where the behavior changes: e89ad9f

Thanks @charlespierce. After reverting that commit and building locally, this error has not happened for me.