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panicked at crates/rust-analyzer/src/handlers/notification.rs:338:25: index out of bounds: the len is 0 but the index is 0 #21638

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@bjorn3

rust-analyzer version: rust-analyzer version: 0.4.2791-standalone [/home/gh-bjorn3/.vscode-server/extensions/rust-lang.rust-analyzer-0.4.2791-linux-arm64/server/rust-analyzer]

rustc version: Rust toolchain is uninstalled.

editor or extension: VSCode

relevant settings: Fairly standard config for the rust repo.

repository link (if public, optional): https://github.com/rust-lang/rust/

Rust-analyzer panics at some point when working on the rust-analyzer repo. Probably related to the fact that the active toolchain was not installed when rust-analyzer started.

Panic happens at

world.flycheck[0].restart_workspace(saved_file);

rust-analyzer failed to load workspace: Failed to load the project at /home/gh-bjorn3/rust/compiler/rustc_codegen_cranelift/Cargo.toml: Failed to read Cargo metadata from Cargo.toml file /home/gh-bjorn3/rust/compiler/rustc_codegen_cranelift/Cargo.toml, None: Failed to run `cd "/home/gh-bjorn3/rust/compiler/rustc_codegen_cranelift" && RUSTC_BOOTSTRAP="1" RUSTUP_AUTO_INSTALL="0" "/home/gh-bjorn3/.cargo/bin/cargo" "metadata" "--format-version" "1" "--manifest-path" "/home/gh-bjorn3/rust/compiler/rustc_codegen_cranelift/Cargo.toml"`: `cargo metadata` exited with an error: error: toolchain 'nightly-aarch64-unknown-linux-gnu' is not installed
help: run `rustup toolchain install` to install it

rust-analyzer failed to load workspace: Failed to load the project at /home/gh-bjorn3/rust/compiler/rustc_codegen_gcc/Cargo.toml: Failed to read Cargo metadata from Cargo.toml file /home/gh-bjorn3/rust/compiler/rustc_codegen_gcc/Cargo.toml, None: Failed to run `cd "/home/gh-bjorn3/rust/compiler/rustc_codegen_gcc" && RUSTC_BOOTSTRAP="1" RUSTUP_AUTO_INSTALL="0" "/home/gh-bjorn3/.cargo/bin/cargo" "metadata" "--format-version" "1" "--manifest-path" "/home/gh-bjorn3/rust/compiler/rustc_codegen_gcc/Cargo.toml"`: `cargo metadata` exited with an error: error: toolchain 'nightly-aarch64-unknown-linux-gnu' is not installed
help: run `rustup toolchain install` to install it

rust-analyzer failed to load workspace: Failed to load the project at /home/gh-bjorn3/rust/library/Cargo.toml: Failed to read Cargo metadata from Cargo.toml file /home/gh-bjorn3/rust/library/Cargo.toml, None: Failed to run `cd "/home/gh-bjorn3/rust/library" && RUSTC_BOOTSTRAP="1" RUSTUP_AUTO_INSTALL="0" "/home/gh-bjorn3/.cargo/bin/cargo" "metadata" "--format-version" "1" "--manifest-path" "/home/gh-bjorn3/rust/library/Cargo.toml"`: `cargo metadata` exited with an error: error: toolchain 'nightly-aarch64-unknown-linux-gnu' is not installed
help: run `rustup toolchain install` to install it

rust-analyzer failed to load workspace: Failed to load the project at /home/gh-bjorn3/rust/src/bootstrap/Cargo.toml: Failed to read Cargo metadata from Cargo.toml file /home/gh-bjorn3/rust/src/bootstrap/Cargo.toml, None: Failed to run `cd "/home/gh-bjorn3/rust/src/bootstrap" && RUSTC_BOOTSTRAP="1" RUSTUP_AUTO_INSTALL="0" "/home/gh-bjorn3/.cargo/bin/cargo" "metadata" "--format-version" "1" "--manifest-path" "/home/gh-bjorn3/rust/src/bootstrap/Cargo.toml"`: `cargo metadata` exited with an error: error: toolchain 'nightly-aarch64-unknown-linux-gnu' is not installed
help: run `rustup toolchain install` to install it

rust-analyzer failed to load workspace: Failed to load the project at /home/gh-bjorn3/rust/src/tools/miri/Cargo.toml: Failed to read Cargo metadata from Cargo.toml file /home/gh-bjorn3/rust/src/tools/miri/Cargo.toml, None: Failed to run `cd "/home/gh-bjorn3/rust/src/tools/miri" && RUSTC_BOOTSTRAP="1" RUSTUP_AUTO_INSTALL="0" "/home/gh-bjorn3/.cargo/bin/cargo" "metadata" "--format-version" "1" "--manifest-path" "/home/gh-bjorn3/rust/src/tools/miri/Cargo.toml"`: `cargo metadata` exited with an error: error: toolchain 'nightly-aarch64-unknown-linux-gnu' is not installed
help: run `rustup toolchain install` to install it


2026-02-13T10:39:40.252927624Z ERROR should have exactly one flycheck handle when invocation strategy is once

thread 'Worker9' (3966083) panicked at crates/rust-analyzer/src/handlers/notification.rs:338:25:
index out of bounds: the len is 0 but the index is 0
stack backtrace:
   0: __rustc::rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::panicking::panic_bounds_check
   3: core::ops::function::FnOnce::call_once{{vtable.shim}}
   4: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
   5: core::ops::function::FnOnce::call_once{{vtable.shim}}
   6: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
2026-02-13T10:39:40.26494485Z ERROR flycheck task panicked: Any { .. }
2026-02-13T10:39:44.844284722Z ERROR should have exactly one flycheck handle when invocation strategy is once

thread 'Worker14' (3966088) panicked at crates/rust-analyzer/src/handlers/notification.rs:338:25:
index out of bounds: the len is 0 but the index is 0
stack backtrace:
   0: __rustc::rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::panicking::panic_bounds_check
   3: core::ops::function::FnOnce::call_once{{vtable.shim}}
   4: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
   5: core::ops::function::FnOnce::call_once{{vtable.shim}}
   6: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
2026-02-13T10:39:44.844620301Z ERROR flycheck task panicked: Any { .. }

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    A-flycheckissues with flycheck a.k.a. "check on save"C-bugCategory: bugE-easyI-panic

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