RA doesn't properly resolve _relative_ env vars from `.cargo/config.toml`

rust-analyzer version: rust-analyzer version: 0.3.2112-standalone (94b526fc8 2024-09-15) [/Users/greg/.vscode/extensions/rust-lang.rust-analyzer-0.3.2112-darwin-arm64/server/rust-analyzer]

rustc version: rustc 1.81.0 (eeb90cda1 2024-09-04)

editor or extension: vscode v0.3.2112

relevant settings:

Any .cargo/config.toml setting a relative env var. For example: https://github.com/rust-lang/rust-analyzer/blob/990c48cb0df6cd6aed2c584dfaa6940406abc28b/.cargo/config.toml#L12-L13

repository link (if public, optional):

code snippet to reproduce:

The [env] table in .cargo/config.toml allows for values to specified as relative paths, in which case they should be resolved to absolute paths that are relative to the .cargo dir. See https://doc.rust-lang.org/cargo/reference/config.html#env. An example is:

[env]
FOO = { value = ".", relative = true }

Rust-Analyzer does not convert this to a proper absolute path.

The relevant code is here:

https://github.com/rust-lang/rust-analyzer/blob/990c48cb0df6cd6aed2c584dfaa6940406abc28b/crates/project-model/src/env.rs#L72-L113

We an see that RA runs a command like: cargo -Zunstable-options config get env, which will output something like the following, assuming the example toml snippet above:

env.FOO.relative = true
env.FOO.value = "."

We can see that RA strips the .value suffix

https://github.com/rust-lang/rust-analyzer/blob/990c48cb0df6cd6aed2c584dfaa6940406abc28b/crates/project-model/src/env.rs#L106

and ignores the .relative field.

A Fix

One way to fix this would be to compute the absolute path by joining the relative path with the config file's path.

Start in crates/project-model/src/env.rs, especially the environment parsing around the cargo config output described in the issue. Reproduce the cargo -Zunstable-options config get env output with an [env] value marked relative = true, then trace how the .value and .relative fields are handled. Done means relative values resolve against the .cargo directory as absolute paths.