rust-analyzer errors out on Nix

[Rua]

Since a few weeks, when running rust-analyzer via vscodium on NixOS, it errors out like this:

[ERROR rust_analyzer::lsp_utils] rust-analyzer failed to load workspace: Failed to read Cargo metadata for Rust sources: Failed to run "cargo" "metadata" "--format-version" "1" "--manifest-path" "/nix/store/3fcjw8dm19ihsxj77ip2w4pnipcv75x9-rust-nightly-with-components-2022-08-08/lib/rustlib/rustc-src/rust/compiler/rustc/Cargo.toml" "--filter-platform" "x86_64-unknown-linux-gnu": cargo metadata exited with an error: Updating crates.io index
error: failed to write /nix/store/3fcjw8dm19ihsxj77ip2w4pnipcv75x9-rust-nightly-with-components-2022-08-08/lib/rustlib/rustc-src/rust/compiler/rustc/Cargo.lock

Caused by:
failed to open: /nix/store/3fcjw8dm19ihsxj77ip2w4pnipcv75x9-rust-nightly-with-components-2022-08-08/lib/rustlib/rustc-src/rust/compiler/rustc/Cargo.lock

Caused by:
Read-only file system (os error 30)

For some reason, it's trying to write to a Cargo.lock file in the Nix store, which is of course not possible.

@cydparser do you also get this?

[kkysen]

We merged #1593 about two weeks ago, which is related to the crates.io index, so maybe that's affecting things?

[cydparser]

I haven't seen that error yet.

[Rua]

I reported it to fenix as well, but they don't think the cause is on their end:
nix-community/fenix#236 (comment)

[Rua]

It seems to be this bug in rust-analyzer/cargo-metadata that got fixed a few years ago: rust-lang/rust-analyzer#10792. But because c2rust is using old nightlies, it doesn't get to profit from that yet. In any case, the problem seems to be related to the rustc-dev component specifically.