Project discovery does not create a valid sysroot

[cameron-martin]

When using rust-analyzer's project discovery, configured very similarly to in the docs, the sysroot that is output does not exist. The only configuration difference is using --output_user_root instead of --output_base, but I doubt this makes a difference.

This is the offending JSON:

"project":{"sysroot":"/home/cameron/.cache/bazel_ra/03e18a5a406e1c59abeb6ec9d1cd7005/external/rules_rust++rust+rust_analyzer_1.86.0_tools","sysroot_src":"/home/cameron/.cache/bazel_ra/03e18a5a406e1c59abeb6ec9d1cd7005/external/rules_rust++rust+rust_analyzer_1.86.0_tools/lib/rustlib/src/library",

Either this sysroot is incorrect, or the project discovery has failed to make bazel fetch this repository.

[cameron-martin]

It seems the sysroot is correct, but the fetch doesn't happen. I currently have a workaround where my discover_bazel_rust_project.sh looks like this:

#!/usr/bin/bash

set -euo pipefail

# Workaround for https://github.com/bazelbuild/rules_rust/issues/3447
bazel --output_user_root=~/.cache/bazel_ra fetch --repo=@@rules_rust++rust+rust_analyzer_1.86.0_tools 2>/dev/null

bazel \
    run \
    @rules_rust//tools/rust_analyzer:discover_bazel_rust_project -- \
    --bazel_startup_option=--output_user_root=~/.cache/bazel_ra \
    --bazel_arg=--watchfs \
    ${1:+"$1"} 2>/dev/null

The most obvious solution here is to make @rules_rust//tools/rust_analyzer:discover_bazel_rust_project run a bazel fetch, but maybe there's a cleverer way to do it during aspect execution.