Rust: pin integration test toolchain to 1.94.1

[redsun82]

Pin the Rust toolchain used by integration tests to 1.94.1 to prevent breakage from runner images that ship newer versions.

Changes

• rust/ql/integration-tests/conftest.py:
  • Add autouse _pin_rust_toolchain fixture that writes a rust-toolchain.toml (pinned to 1.94.1 with rust-src component) into each test's working directory
  • Update rust_sysroot_src to use rustc +1.94.1 and explicitly ensure rust-src is installed

No changes to rust/ql/test/rust-toolchain.toml — QL language tests are unaffected.

[Copilot]

Pull request overview

Pins the Rust toolchain used by the Rust integration tests to the version declared in rust/ql/test/rust-toolchain.toml, aiming to make CI test behavior independent of whatever Rust is preinstalled on the runner image.

Changes:

• Bump Rust test toolchain channel from 1.90 to 1.94.1.
• Add an autouse pytest fixture to set RUSTUP_TOOLCHAIN based on the shared rust-toolchain.toml.
• Update sysroot discovery to call rustc +{channel} --print sysroot to ensure the pinned toolchain is used.

Show a summary per file

File	Description
rust/ql/test/rust-toolchain.toml	Updates the pinned Rust channel used by Rust QL tests.
rust/ql/integration-tests/conftest.py	Reads the pinned channel and attempts to enforce it for integration tests via env var + rustc +toolchain.

Copilot's findings

Comments suppressed due to low confidence (1)

rust/ql/integration-tests/conftest.py:20

• This autouse fixture mutates os.environ but never restores the previous value. Since environment variables are process-global, this can leak into later tests outside rust/ql/integration-tests when running a larger pytest suite. Prefer setting the variable via monkeypatch.setenv(...) (auto-restored), or implement a yield fixture that restores/deletes RUSTUP_TOOLCHAIN afterwards (potentially with scope="session" if you only need to set it once).

@pytest.fixture(autouse=True)
def _pin_rust_toolchain(environment):
    """Pin the Rust toolchain to the version specified in ql/test/rust-toolchain.toml.

    Integration tests run from temporary directories, so they don't pick up the
    rust-toolchain.toml file via rustup's file-based resolution. Setting
    RUSTUP_TOOLCHAIN ensures a consistent version regardless of the runner image.
    """
    os.environ["RUSTUP_TOOLCHAIN"] = _toolchain_channel

• Files reviewed: 2/2 changed files
• Comments generated: 1

[redsun82]

No longer needed — toolchain pinning will be handled entirely in the semmle-code prepare action via RUSTUP_TOOLCHAIN env var.