Rust: Preinstall extractor toolchain in tests

Install the fixed toolchain used by the extractor before parallel
integration and QL tests start. This avoids concurrent rustup
auto-installation races.

Author: paldepind

rust/ql/integration-tests/conftest.py

@@ -5,6 +5,16 @@
 import tomllib
 
 
+def pytest_configure(config):
+    # Install the fixed toolchain used by the extractor before xdist starts its
+    # workers to avoid concurrent rustup downloads. The version here should
+    # match `FIXED_RUST_TOOLCHAIN`.
+    if not hasattr(config, "workerinput"):
+        commands.run(
+            "rustup toolchain install 1.97.0 --profile minimal --component rust-src"
+        )
+
+
 @pytest.fixture(params=[2018, 2021, 2024])
 def rust_edition(request):
     return request.param

rust/ql/test/setup.sh

@@ -8,6 +8,9 @@ set -euo pipefail
 
 # no need to install rust-src explicitly, it's listed in both toolchains
 cd "$(dirname "$0")"
+# Install the fixed toolchain used by the extractor. The version here should
+# match `FIXED_RUST_TOOLCHAIN`.
+rustup toolchain install 1.97.0 --profile minimal --component rust-src
 pushd ../../extractor/src/nightly-toolchain
 rustup install
 popd