Rust toolchain

Rust toolchain for external modules

CREATE MODULE compiles Rust sources through the local toolchain, so every machine that runs queries over external modules needs one. Two code paths in qdb/catalog/external_module.cpp invoke it:

• native modules — rustc <src> --emit llvm-bc, and qdb/utils/rust_std_loader.cpp then dlopens libstd from rustc --print target-libdir;
• wasm64 modules — cargo rustc --target wasm64-unknown-unknown --release -Z build-std=std,panic_abort with RUSTC_BOOTSTRAP=1, because Rust ships no prebuilt wasm64 std.

Two consequences follow. The rust-src component is mandatory (build-std compiles std from source), and the Rust release must match the LLVM the engine links against: LLVM 20 pairs with Rust 1.90.0, the version pinned in .github/workflows/c-cpp.yml. A newer stable emits bitcode LLVM 20 refuses to read.

Packaged service

The service runs as the system user qumirdb with no home of its own, so a per-user rustup install is not there and requests fail with:

rustup could not choose a version of cargo to run, because one wasn't specified
explicitly, and no default is configured

Install the toolchain system-wide instead of into a home directory:

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs -o /tmp/rustup-init.sh
sudo env RUSTUP_HOME=/opt/rust/rustup CARGO_HOME=/opt/rust/cargo \
     sh /tmp/rustup-init.sh -y --no-modify-path --profile minimal \
     --default-toolchain 1.90.0 --component rust-src
sudo chmod -R a+rX /opt/rust

Give the service a writable CARGO_HOME (cargo keeps .package-cache and the registry index there) and point it at the toolchain through a systemd drop-in, leaving the packaged unit untouched:

sudo install -d -o qumirdb -g qumirdb /var/lib/qumirdb-data/cargo
sudo systemctl edit qumirdb-service

[Service]
Environment=RUSTUP_HOME=/opt/rust/rustup
Environment=RUSTUP_TOOLCHAIN=1.90.0
Environment=CARGO_HOME=/var/lib/qumirdb-data/cargo
Environment=PATH=/opt/rust/cargo/bin:/usr/local/bin:/usr/bin:/bin

RUSTUP_TOOLCHAIN pins the version without depending on whose rustup default was configured; PATH matters because the engine execs cargo/rustc directly, and systemd's default PATH does not include /opt/rust/cargo/bin. Add Environment=CARGO_NET_OFFLINE=true on hosts without network access — build-std needs no crates beyond rust-src.

Then restart and verify as the service user:

sudo systemctl daemon-reload
sudo systemctl restart qumirdb-service

sudo -u qumirdb env HOME=/var/lib/qumirdb-data \
     RUSTUP_HOME=/opt/rust/rustup RUSTUP_TOOLCHAIN=1.90.0 \
     CARGO_HOME=/var/lib/qumirdb-data/cargo PATH=/opt/rust/cargo/bin:$PATH \
     sh -c 'rustc --version; cargo --version; rustc --print target-libdir'

It must print rustc 1.90.0, cargo 1.90.0 and an existing target-libdir; the last one is the directory the engine loads libstd from.

Development machines

A normal per-user install is enough — the same pinned release and component:

rustup toolchain install 1.90.0 --profile minimal --component rust-src
export RUSTUP_TOOLCHAIN=1.90.0