Rust: refine ql/test/setup.sh

rust/ql/test/setup.sh

@@ -5,13 +5,13 @@ set -euo pipefail
 # This script is run by the CI to set up the test environment for the Rust QL tests
 # We run this as rustup is not meant to be run in parallel, and will this setup will be run by rust-analyzer in the
 # parallel QL tests unless we do the setup prior to launching the tests.
-# We do this for each `rust-toolchain.toml` we use in the tests (and the root one in `rust`)
+# We do this for each `rust-toolchain.toml` we use in the tests (and the root one in `rust` last, so it becomes the
+# default).
+# Notice that we do not need to explicitly add the rust-std component as it's listed in ql/rust/rust-toolchain.toml.
 
 cd "$(dirname "$0")"
 
-rustup install
-rustup component add rust-src
-
 find . -name rust-toolchain.toml \
-  -execdir rustup install \; \
-  -execdir rustup component add rust-src \;
+  -execdir rustup install \;
+
+rustup install