Description
openedon Nov 18, 2021
Problem
I first reported this with rust-analyzer at rust-lang/rust-analyzer#10792: when running cargo metadata on a read-only file system, it fails saying
rust-analyzer failed to load workspace: Failed to read Cargo metadata for Rust sources: Failed to run `cargo metadata --manifest-path /home/r/.rustup/toolchains/miri/lib/rustlib/rustc-src/rust/compiler/rustc/Cargo.toml`: `cargo metadata` exited with an error: Updating crates.io index
error: failed to write /home/r/.rustup/toolchains/miri/lib/rustlib/rustc-src/rust/compiler/rustc/Cargo.lock
Caused by:
failed to open: /home/r/.rustup/toolchains/miri/lib/rustlib/rustc-src/rust/compiler/rustc/Cargo.lock
Caused by:
Read-only file system (os error 30)
rust-analyzer failed to load workspace: Failed to read Cargo metadata for Rust sources: Failed to run `cargo metadata --manifest-path /home/r/.rustup/toolchains/miri/lib/rustlib/rustc-src/rust/compiler/rustc/Cargo.toml`: `cargo metadata` exited with an error: Updating crates.io index
error: failed to write /home/r/.rustup/toolchains/miri/lib/rustlib/rustc-src/rust/compiler/rustc/Cargo.lock
Caused by:
failed to open: /home/r/.rustup/toolchains/miri/lib/rustlib/rustc-src/rust/compiler/rustc/Cargo.lock
Caused by:
Read-only file system (os error 30)
However, the action RA is trying to perform is fundamentally a read-only operation (querying for information about the rustc compiler crates).
I don't think the currently available flags provide any way to make this work on a read-only file system either (I tried --frozen but as expected it refuses to download required crates from the network). Even if my toolchain was on a read-write file system I would not want RA's cargo metadata to change toolchain files, after all.
Proposed Solution
cargo metadata should either handle read-only file systems by falling back to not creating/updating the lock file -- or (IMO the right fix) it should not even attempt to mutate the workspace when what it is doing is a read-only operation like just determining the metadata.
Notes
No response