`index out of bounds` panic in `chalk_ir::SubstFolder::fold_free_var_ty`

[str4d]

Environment

• VSCode version: 1.59.1, Windows 10 with repo open in WSL remote.
• rust-analyzer version: 996300f 2021-08-23 stable

To reproduce

• Set up VSCode with the rust-analyzer plugin.
• Check out https://github.com/zkcrypto/bellman/tree/2021-08-26-rust-analyzer-multiexp-bug
• Open src/multiexp.rs in VSCode editor window.

Result

rust-analyzer panics twice: once at position 0,0, and again at a position within a line or so of my cursor. Any time I move my cursor (or I think even move my mouse above the multiexp.rs editor pane), another panic is triggered within a second or so.

Panic output

Panic context:
> 
version: 996300f4a 2021-08-23 stable
request: textDocument/codeAction CodeActionParams {
    text_document: TextDocumentIdentifier {
        uri: Url {
            scheme: "file",
            cannot_be_a_base: false,
            username: "",
            password: None,
            host: None,
            port: None,
            path: "/home/str4d/dev/rust/zkcrypto/bellman/src/multiexp.rs",
            query: None,
            fragment: None,
        },
    },
    range: Range {
        start: Position {
            line: 0,
            character: 0,
        },
        end: Position {
            line: 0,
            character: 0,
        },
    },
    context: CodeActionContext {
        diagnostics: [],
        only: None,
    },
    work_done_progress_params: WorkDoneProgressParams {
        work_done_token: None,
    },
    partial_result_params: PartialResultParams {
        partial_result_token: None,
    },
}

thread '<unnamed>' panicked at 'index out of bounds: the len is 1 but the index is 1', /home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/chalk-ir-0.70.0/src/lib.rs:2752:10
stack backtrace:
   0: rust_begin_unwind
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/std/src/panicking.rs:515:5
   1: core::panicking::panic_fmt
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/core/src/panicking.rs:92:14
   2: core::panicking::panic_bounds_check
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/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::Ty<I> as chalk_ir::fold::SuperFold<I>>::super_fold_with
  10: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_method_call
  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_method_call
  14: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
  15: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_coerce
  16: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_block
  17: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
  18: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_coerce
  19: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_block
  20: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
  21: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
  22: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_coerce
  23: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_block
  24: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
  25: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr
  26: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
  27: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_coerce
  28: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_block
  29: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
  30: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_coerce
  31: hir_ty::infer::infer_query
  32: salsa::runtime::Runtime::execute_query_implementation
  33: salsa::derived::slot::Slot<Q,MP>::read_upgrade
  34: salsa::derived::slot::Slot<Q,MP>::read
  35: <salsa::derived::DerivedStorage<Q,MP> as salsa::plumbing::QueryStorageOps<Q>>::try_fetch
  36: <DB as hir_ty::db::HirDatabase>::infer_query
  37: hir_ty::db::infer_wait
  38: hir::Function::diagnostics
  39: hir::Module::diagnostics
  40: ide_diagnostics::diagnostics
  41: ide::Analysis::assists_with_fixes::{{closure}}
  42: std::panicking::try
  43: rust_analyzer::handlers::handle_code_action
  44: rust_analyzer::dispatch::RequestDispatcher::on::{{closure}}::{{closure}}
  45: <F as threadpool::FnBox>::call_box
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
Panic context:
> 
version: 996300f4a 2021-08-23 stable
request: rust-analyzer/inlayHints InlayHintsParams {
    text_document: TextDocumentIdentifier {
        uri: Url {
            scheme: "file",
            cannot_be_a_base: false,
            username: "",
            password: None,
            host: None,
            port: None,
            path: "/home/str4d/dev/rust/zkcrypto/bellman/src/multiexp.rs",
            query: None,
            fragment: None,
        },
    },
}

thread '<unnamed>' panicked at 'index out of bounds: the len is 1 but the index is 1', /home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/chalk-ir-0.70.0/src/lib.rs:2752:10
stack backtrace:
   0: rust_begin_unwind
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/std/src/panicking.rs:515:5
   1: core::panicking::panic_fmt
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/core/src/panicking.rs:92:14
   2: core::panicking::panic_bounds_check
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/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::Ty<I> as chalk_ir::fold::SuperFold<I>>::super_fold_with
  10: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_method_call
  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_method_call
  14: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
  15: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_coerce
  16: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_block
  17: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
  18: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_coerce
  19: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_block
  20: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
  21: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
  22: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_coerce
  23: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_block
  24: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
  25: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr
  26: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
  27: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_coerce
  28: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_block
  29: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
  30: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_coerce
  31: hir_ty::infer::infer_query
  32: salsa::runtime::Runtime::execute_query_implementation
  33: salsa::derived::slot::Slot<Q,MP>::read_upgrade
  34: salsa::derived::slot::Slot<Q,MP>::read
  35: <salsa::derived::DerivedStorage<Q,MP> as salsa::plumbing::QueryStorageOps<Q>>::try_fetch
  36: <DB as hir_ty::db::HirDatabase>::infer_query
  37: hir_ty::db::infer_wait
  38: hir::semantics::SemanticsImpl::analyze_impl
  39: hir::semantics::SemanticsImpl::scope
  40: ide::inlay_hints::inlay_hints
  41: std::panicking::try
  42: rust_analyzer::handlers::handle_inlay_hints
  43: rust_analyzer::dispatch::RequestDispatcher::on::{{closure}}::{{closure}}
  44: <F as threadpool::FnBox>::call_box
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
Panic context:
> 
version: 996300f4a 2021-08-23 stable
request: textDocument/codeAction CodeActionParams {
    text_document: TextDocumentIdentifier {
        uri: Url {
            scheme: "file",
            cannot_be_a_base: false,
            username: "",
            password: None,
            host: None,
            port: None,
            path: "/home/str4d/dev/rust/zkcrypto/bellman/src/multiexp.rs",
            query: None,
            fragment: None,
        },
    },
    range: Range {
        start: Position {
            line: 15,
            character: 18,
        },
        end: Position {
            line: 15,
            character: 18,
        },
    },
    context: CodeActionContext {
        diagnostics: [],
        only: None,
    },
    work_done_progress_params: WorkDoneProgressParams {
        work_done_token: None,
    },
    partial_result_params: PartialResultParams {
        partial_result_token: None,
    },
}

thread '<unnamed>' panicked at 'index out of bounds: the len is 1 but the index is 1', /home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/chalk-ir-0.70.0/src/lib.rs:2752:10
stack backtrace:
   0: rust_begin_unwind
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/std/src/panicking.rs:515:5
   1: core::panicking::panic_fmt
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/core/src/panicking.rs:92:14
   2: core::panicking::panic_bounds_check
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/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::Ty<I> as chalk_ir::fold::SuperFold<I>>::super_fold_with
  10: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_method_call
  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_method_call
  14: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
  15: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_coerce
  16: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_block
  17: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
  18: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_coerce
  19: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_block
  20: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
  21: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
  22: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_coerce
  23: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_block
  24: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
  25: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr
  26: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
  27: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_coerce
  28: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_block
  29: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_inner
  30: hir_ty::infer::expr::<impl hir_ty::infer::InferenceContext>::infer_expr_coerce
  31: hir_ty::infer::infer_query
  32: salsa::runtime::Runtime::execute_query_implementation
  33: salsa::derived::slot::Slot<Q,MP>::read_upgrade
  34: salsa::derived::slot::Slot<Q,MP>::read
  35: <salsa::derived::DerivedStorage<Q,MP> as salsa::plumbing::QueryStorageOps<Q>>::try_fetch
  36: <DB as hir_ty::db::HirDatabase>::infer_query
  37: hir_ty::db::infer_wait
  38: hir::Function::diagnostics
  39: hir::Module::diagnostics
  40: ide_diagnostics::diagnostics
  41: ide::Analysis::assists_with_fixes::{{closure}}
  42: std::panicking::try
  43: rust_analyzer::handlers::handle_code_action
  44: rust_analyzer::dispatch::RequestDispatcher::on::{{closure}}::{{closure}}
  45: <F as threadpool::FnBox>::call_box
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

[Halkcyon]

This looks like the same problem as #5366

I ran into this problem while using rltk::SmallVec<[(usize, f32); 10]>::push; the auto-complete of the method name caused the error to be thrown every time after tying pu.

[lnicola]

If you look at the stack trace, this is unrelated to #5366.

Do you have a repro for either of the problems?

[flodiebold]

Minimized it to the following test:

#[test]
fn bitslice_panic() {
    check_no_mismatches(
        r#"
//- minicore: option, deref

pub trait BitView {
    type Store;
}

pub struct Lsb0;

pub struct BitArray<V: BitView> { }

pub struct BitSlice<T> { }

impl<V: BitView> core::ops::Deref for BitArray<V> {
    type Target = BitSlice<V::Store>;
}

impl<T> BitSlice<T> {
    pub fn split_first(&self) -> Option<(T, &Self)> { loop {} }
}

fn multiexp_inner() {
    let exp: &BitArray<Foo>;
    exp.split_first();
}
        "#,
    );
}