feat(rust): expression graph, typed IR, evaluator and forward-mode AD

.github/scripts/run_cargo.py

@@ -0,0 +1,26 @@
+"""Run `cargo` with the given arguments, or skip where no Rust toolchain is installed.
+
+The cargo pre-commit hooks go through this so that `pre-commit run --all-files` works
+without Rust; CI installs Rust, so the `style` job still runs them.
+"""
+
+from __future__ import annotations
+
+import shutil
+import subprocess
+import sys
+
+
+def main() -> int:
+    cargo = shutil.which("cargo")
+    if cargo is None:
+        print(
+            "cargo is not on PATH, so this Rust hook is skipped; install Rust "
+            "(https://rustup.rs) to run it."
+        )
+        return 0
+    return subprocess.call([cargo, *sys.argv[1:]])
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())

.github/workflows/codeql.yml

@@ -25,7 +25,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        language: [python, c-cpp]
+        language: [python, c-cpp, rust]
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with:

.github/workflows/test_on_push.yml

@@ -59,6 +59,7 @@ jobs:
               - '.github/workflows/_build_solver_wheels.yml'
             pybamm:
               - 'packages/pybamm/**'
+              - 'packages/pybamm-rust/**'
               - 'pyproject.toml'
               - 'uv.lock'
               - 'noxfile.py'
@@ -103,6 +104,50 @@ jobs:
             echo "macos_runners=$macos"
           } >> "$GITHUB_OUTPUT"
 
+  rust_msrv:
+    needs: changes
+    if: ${{ github.event_name == 'push' || needs.changes.outputs.pybamm == 'true' }}
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+    name: Rust MSRV (1.89)
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+      - name: Install the MSRV toolchain
+        run: rustup toolchain install 1.89 --profile minimal --no-self-update
+      - uses: Swatinem/rust-cache@c19371144df3bb44fab255c43d04cbc2ab54d1c4 # v2.9.1
+        with:
+          workspaces: packages/pybamm-rust
+          key: msrv-1.89
+          save-if: ${{ github.ref == 'refs/heads/main' }}
+      - name: Check against the declared MSRV
+        run: >
+          cargo +1.89 check --manifest-path packages/pybamm-rust/Cargo.toml
+          --locked --all-targets --all-features
+
+  rust_tests:
+    needs: changes
+    if: ${{ github.event_name == 'push' || needs.changes.outputs.pybamm == 'true' }}
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+    name: Rust tests
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+      - uses: Swatinem/rust-cache@c19371144df3bb44fab255c43d04cbc2ab54d1c4 # v2.9.1
+        with:
+          workspaces: packages/pybamm-rust
+          key: tests
+          save-if: ${{ github.ref == 'refs/heads/main' }}
+      - name: Run the Rust test suite
+        run: >
+          cargo test --manifest-path packages/pybamm-rust/Cargo.toml
+          --locked --workspace --all-features
+
   style:
     runs-on: ubuntu-latest
     permissions:
@@ -125,6 +170,15 @@ jobs:
         with:
           python-version: 3.12
 
+      # Pinned, as each Rust release adds pedantic and nursery lints that `-D warnings` fails on.
+      - name: Install the pinned Rust toolchain
+        run: |
+          rustup toolchain install 1.99.1 --profile minimal --component clippy,rustfmt --no-self-update
+          rustup default 1.99.1
+      - uses: Swatinem/rust-cache@c19371144df3bb44fab255c43d04cbc2ab54d1c4 # v2.9.1
+        with:
+          workspaces: packages/pybamm-rust
+          save-if: ${{ github.ref == 'refs/heads/main' }}
       - uses: astral-sh/setup-uv@1c37ad07a6a961277cf70c0d37d6f313000f5884 # v10.3.0
         with:
           version: "latest"
@@ -355,6 +409,8 @@ jobs:
     needs:
       - changes
       - style
+      - rust_msrv
+      - rust_tests
       - build_solver
       - run_unit_tests
       - run_coverage

.pre-commit-config.yaml

@@ -2,8 +2,8 @@ ci:
   autoupdate_commit_msg: "chore: update pre-commit hooks"
   autofix_commit_msg: "style: pre-commit fixes"
   autoupdate_schedule: "weekly"
-  # No base ref here, so comment-slop would scan nothing; `style` gates it.
-  skip: [comment-slop]
+  # No base ref or Rust toolchain here; the `style` CI job gates these.
+  skip: [comment-slop, cargo-fmt, cargo-clippy]
 
 repos:
   - repo: https://github.com/astral-sh/ruff-pre-commit
@@ -83,3 +83,19 @@ repos:
         additional_dependencies: [pyyaml]
         files: ^\.github/(workflows/test_on_push\.yml|scripts/check_ci_gate\.py)$
         pass_filenames: false
+      # Skipped, saying so, where cargo is not installed.
+      - id: cargo-fmt
+        name: cargo fmt
+        entry: python .github/scripts/run_cargo.py fmt --manifest-path packages/pybamm-rust/Cargo.toml --all
+        language: python
+        types: [rust]
+        pass_filenames: false
+        verbose: true
+      - id: cargo-clippy
+        name: cargo clippy
+        entry: python .github/scripts/run_cargo.py clippy --quiet --manifest-path packages/pybamm-rust/Cargo.toml --all-targets --all-features
+        language: python
+        types: [rust]
+        pass_filenames: false
+        verbose: true
+        args: ["--", "-D", "warnings"]

CHANGELOG.md

@@ -8,6 +8,8 @@
 ## Features
 
 - Replaced Codacy with open checks that also run locally. Ruff's `flake8-bandit` (`S`) rules replace Bandit, and CodeQL scans the Python and C++ code. `nox -s type-check` runs Pyrefly over `pybamm`, which now type-checks cleanly, and a new type error fails CI. clang-tidy reports solver findings to code scanning as an advisory check. ([#5974](https://github.com/pybamm-team/PyBaMM/pull/5974))
+- Added `pybamm-core` (`packages/pybamm-rust`), a Rust expression compiler: an arena DAG with simplification, CSE and zero propagation, a typed IR, scalar and lane-batched interpreters, and forward-mode AD. CI runs `cargo test`, an MSRV check, `cargo fmt`, `cargo clippy` and CodeQL. ([#5956](https://github.com/pybamm-team/PyBaMM/pull/5956))
+- `pybamm-core` evaluates transcendentals through the platform C library, as CasADi does: bitwise identical across evaluation paths, last-bit differences across platforms. `pow` is exact for exponents `0`, `1`, `2` and `-1`; `erf`, `asinh` and IEEE 754-2019 `minimum`/`maximum` use `libm`. ([#5956](https://github.com/pybamm-team/PyBaMM/pull/5956))
 
 ## Bug fixes
 

packages/pybamm-rust/.gitignore

@@ -0,0 +1,7 @@
+/target/
+*/target/
+*.so
+*.dylib
+*.pyd
+.venv/
+uv.lock