chore: Rust-C++ cmake and CI integration (#7034)

.codecov.yml

@@ -1,10 +1,32 @@
 codecov:
   require_ci_to_pass: true
+  # The C++ and Rust uploads land minutes apart; without this gate Codecov
+  # publishes a near-zero total from whichever one arrives first.
+  notify:
+    after_n_builds: 2
+    wait_for_ci: true
 
 comment:
   behavior: default
   layout: reach,diff,flags,tree,reach
-  show_carryforward_flags: false
+  show_carryforward_flags: true
+  after_n_builds: 2
+
+# C++ and Rust coverage upload from independent workflows under the `cpp` and
+# `rust` flags; carryforward keeps one language's total when only the other reran.
+flag_management:
+  default_rules:
+    carryforward: true
+  individual_flags:
+    - name: cpp
+      carryforward: true
+      paths:
+        - include/
+        - src/
+    - name: rust
+      carryforward: true
+      paths:
+        - crates/
 
 coverage:
   range: "70..85"

.cspell.config.yaml

@@ -318,6 +318,7 @@ words:
   - summands
   - superpeer
   - superpeers
+  - Swatinem
   - takergets
   - takerpays
   - ters

.github/dependabot.yml

@@ -19,3 +19,19 @@ updates:
       github-actions:
         patterns:
           - "*"
+
+  - package-ecosystem: cargo
+    directory: /crates
+    schedule:
+      interval: weekly
+      day: monday
+      time: "04:00"
+      timezone: Etc/GMT
+    commit-message:
+      prefix: "chore: [DEPENDABOT] "
+    target-branch: develop
+    open-pull-requests-limit: 10
+    groups:
+      rust-dependencies:
+        patterns:
+          - "*"

.github/scripts/strategy-matrix/generate.py

@@ -7,7 +7,13 @@ from pathlib import Path
 
 THIS_DIR = Path(__file__).parent.resolve()
 
-_BASE_CMAKE_ARGS = ["-Dtests=ON", "-Dwerr=ON", "-Dxrpld=ON", "-Dwextra=ON"]
+_BASE_CMAKE_ARGS = [
+    "-Dtests=ON",
+    "-Dwerr=ON",
+    "-Dxrpld=ON",
+    "-Dwextra=ON",
+    "-Drust=ON",
+]
 
 # Maps sanitizer names (as used in cmake) to short config-name suffixes.
 _SANITIZER_SUFFIX: dict[str, str] = {

.github/workflows/cargo-audit.yml

@@ -0,0 +1,80 @@
+name: Cargo audit
+
+on:
+  schedule:
+    # 06:32 UTC every Monday.
+    - cron: "32 6 * * 1"
+  push:
+    branches:
+      - "develop"
+      - "release/*"
+    paths:
+      - "crates/**/Cargo.toml"
+      - "crates/Cargo.lock"
+      - ".github/workflows/cargo-audit.yml"
+  pull_request:
+    paths:
+      - "crates/**/Cargo.toml"
+      - "crates/Cargo.lock"
+      - ".github/workflows/cargo-audit.yml"
+  workflow_dispatch:
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+defaults:
+  run:
+    shell: bash
+    working-directory: crates
+
+permissions:
+  contents: read
+
+jobs:
+  audit:
+    runs-on: ubuntu-latest
+    container: ghcr.io/xrplf/xrpld/nix-ubuntu:sha-a0074f8
+    permissions:
+      contents: read
+      # Needed to open an issue on scheduled failures.
+      issues: write
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+
+      - name: Run cargo audit
+        id: audit
+        continue-on-error: true
+        run: |
+          set -o pipefail
+          cargo audit | tee /tmp/cargo-audit.txt
+
+      - name: Prepare issue body
+        if: ${{ steps.audit.outcome != 'success' && github.event_name == 'schedule' }}
+        run: |
+          {
+              echo "## \`cargo audit\` found advisories"
+              echo
+              echo '```'
+              cat /tmp/cargo-audit.txt
+              echo '```'
+              echo
+              echo "---"
+              echo "*This issue was automatically created by the cargo-audit workflow.*"
+          } >/tmp/cargo-audit-issue.md
+
+      - name: Create issue
+        if: ${{ steps.audit.outcome != 'success' && github.event_name == 'schedule' }}
+        uses: XRPLF/actions/create-issue@2b8bc36af85b88bca0dd7bfac2e2dc05f94ad712
+        with:
+          title: "cargo audit found vulnerabilities"
+          body_file: /tmp/cargo-audit-issue.md
+          labels: "Bug,Security"
+
+      - name: Fail if advisories were found
+        if: ${{ steps.audit.outcome != 'success' }}
+        run: |
+          echo "cargo audit found advisories!"
+          cat /tmp/cargo-audit.txt
+          exit 1

.github/workflows/check-tools.yml

@@ -79,7 +79,7 @@ jobs:
         uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
 
       - name: Prepare runner
-        uses: XRPLF/actions/prepare-runner@c00c22ada3bd6bcda48fcb0d62fbbab49fec8a0f
+        uses: XRPLF/actions/prepare-runner@51af40f99ea91a08c3528ddf16d98132dcc7e63c
         with:
           enable_ccache: false
 

.github/workflows/on-pr.yml

@@ -86,6 +86,7 @@ jobs:
             .github/workflows/reusable-check-autogen.yml
             .github/workflows/reusable-clang-tidy.yml
             .github/workflows/reusable-package.yml
+            .github/workflows/reusable-rust.yml
             .github/workflows/reusable-strategy-matrix.yml
             .github/workflows/reusable-test.yml
             .github/workflows/reusable-upload-recipe.yml
@@ -97,6 +98,7 @@ jobs:
             cfg/**
             cmake/**
             conan/**
+            crates/**
             external/**
             include/**
             src/**
@@ -173,6 +175,13 @@ jobs:
     secrets:
       CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
 
+  rust:
+    needs: should-run
+    if: ${{ needs.should-run.outputs.go == 'true' }}
+    uses: ./.github/workflows/reusable-rust.yml
+    secrets:
+      CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
+
   package:
     needs: [should-run, build-test]
     # Packaging consumes the debian/rhel release binaries, which are only built
@@ -216,6 +225,7 @@ jobs:
       - check-rename
       - clang-tidy
       - build-test
+      - rust
       - package
       - upload-recipe
       - notify-clio

.github/workflows/on-trigger.yml

@@ -24,6 +24,7 @@ on:
       - ".github/workflows/reusable-check-autogen.yml"
       - ".github/workflows/reusable-clang-tidy.yml"
       - ".github/workflows/reusable-package.yml"
+      - ".github/workflows/reusable-rust.yml"
       - ".github/workflows/reusable-strategy-matrix.yml"
       - ".github/workflows/reusable-test.yml"
       - ".github/workflows/reusable-upload-recipe.yml"
@@ -35,6 +36,7 @@ on:
       - "cfg/**"
       - "cmake/**"
       - "conan/**"
+      - "crates/**"
       - "external/**"
       - "include/**"
       - "src/**"
@@ -101,6 +103,11 @@ jobs:
     secrets:
       CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
 
+  rust:
+    uses: ./.github/workflows/reusable-rust.yml
+    secrets:
+      CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
+
   upload-recipe:
     needs: build-test
     # Only run when pushing to the develop branch.

.github/workflows/publish-docs.yml

@@ -47,7 +47,7 @@ jobs:
         uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
 
       - name: Prepare runner
-        uses: XRPLF/actions/prepare-runner@c00c22ada3bd6bcda48fcb0d62fbbab49fec8a0f
+        uses: XRPLF/actions/prepare-runner@51af40f99ea91a08c3528ddf16d98132dcc7e63c
         with:
           enable_ccache: false
 

.github/workflows/reusable-build-test-config.yml

@@ -129,7 +129,7 @@ jobs:
         uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
 
       - name: Prepare runner
-        uses: XRPLF/actions/prepare-runner@c00c22ada3bd6bcda48fcb0d62fbbab49fec8a0f
+        uses: XRPLF/actions/prepare-runner@51af40f99ea91a08c3528ddf16d98132dcc7e63c
         with:
           enable_ccache: ${{ inputs.ccache_enabled }}
 
@@ -162,6 +162,19 @@ jobs:
         with:
           compiler: ${{ inputs.compiler }}
 
+      - name: Use cargo artifacts cache
+        uses: Swatinem/rust-cache@6323deb102c322ba6fcbdcafc7e3dddab59af2b6 # v2.9.2
+        with:
+          cache-directories: ${{ env.BUILD_DIR }}/corrosion
+          key: ${{ inputs.config_name }}
+          save-if: ${{ github.ref == 'refs/heads/develop' || startsWith(github.ref, 'refs/heads/release') }}
+          # two workspaces here because build artifacts are located in 2 places:
+          # - crates/target when cargo is called directly
+          # - build/cargo when cargo is called by cmake
+          workspaces: |
+            crates
+            crates -> ${{ runner.os == 'Windows' && format('../{0}/x64/{1}/cargo', env.BUILD_DIR, inputs.build_type) || format('../{0}/cargo', env.BUILD_DIR) }}
+
       # `setup-nix-env` already did this for the Nix toolchain.
       - name: Setup Conan
         if: ${{ inputs.toolchain != 'nix' }}
@@ -357,6 +370,11 @@ jobs:
 
           LD_PRELOAD="$PRELOAD" ./xrpld --unittest --unittest-jobs "${BUILD_NPROC}" 2>&1 | tee "${GITHUB_WORKSPACE}/unittest.log"
 
+      - name: Run Rust tests
+        if: ${{ !inputs.build_only }}
+        working-directory: crates
+        run: cargo nextest run --workspace --all-features --locked --no-tests=warn
+
       # Smoke-run every benchmark module with a single repetition to confirm the
       # benchmarks still build and execute. This is a correctness check, not a
       # performance measurement, so there is nothing to gain from repeating it
@@ -428,6 +446,7 @@ jobs:
           disable_telem: true
           fail_ci_if_error: true
           files: ${{ env.BUILD_DIR }}/coverage.xml
+          flags: cpp
           plugins: noop
           token: ${{ secrets.CODECOV_TOKEN }}
           verbose: true

.github/workflows/reusable-clang-tidy.yml

@@ -43,7 +43,7 @@ jobs:
         uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
 
       - name: Prepare runner
-        uses: XRPLF/actions/prepare-runner@c00c22ada3bd6bcda48fcb0d62fbbab49fec8a0f
+        uses: XRPLF/actions/prepare-runner@51af40f99ea91a08c3528ddf16d98132dcc7e63c
         with:
           enable_ccache: false
 
@@ -59,6 +59,13 @@ jobs:
         with:
           compiler: ${{ env.COMPILER }}
 
+      - name: Use cargo artifacts cache
+        uses: Swatinem/rust-cache@6323deb102c322ba6fcbdcafc7e3dddab59af2b6 # v2.9.2
+        with:
+          cache-directories: ${{ env.BUILD_DIR }}/corrosion
+          save-if: ${{ github.ref == 'refs/heads/develop' || startsWith(github.ref, 'refs/heads/release') }}
+          workspaces: crates -> ../${{ env.BUILD_DIR }}/cargo
+
       - name: Setup Conan
         uses: ./.github/actions/setup-conan
 
@@ -80,13 +87,13 @@ jobs:
               -Dwerr=ON \
               -Dxrpld=ON \
               -Dverify_headers=ON \
+              -Drust=ON \
               ..
 
-      # clang-tidy needs headers generated from proto files
-      - name: Build libxrpl.libpb
+      - name: Build clang-tidy prerequisites
         working-directory: ${{ env.BUILD_DIR }}
         run: |
-          ninja -j ${{ steps.nproc.outputs.nproc }} xrpl.libpb
+          ninja -j ${{ steps.nproc.outputs.nproc }} tidy_prerequisites
 
       - name: Run clang tidy
         id: run_clang_tidy

.github/workflows/reusable-rust.yml

@@ -0,0 +1,86 @@
+# Clippy, coverage and documentation for the Rust crates in crates/. Each runs
+# as an independent job on a GitHub-hosted runner, but inside the same container
+# image used to build the crates in the C++/Corrosion path, so the toolchain
+# (and therefore the lints, coverage instrumentation and the cargo cache) matches
+# what production builds use.
+#
+# Rust unit tests are deliberately NOT run here. They run as part of the C++
+# build (reusable-build-test-config.yml), which already compiles the crates on a
+# self-hosted runner, so there is no need to provision a toolchain again.
+name: Rust
+
+on:
+  workflow_call:
+    secrets:
+      CODECOV_TOKEN:
+        description: "The Codecov token to use for uploading coverage reports."
+        required: true
+
+defaults:
+  run:
+    shell: bash
+    working-directory: crates
+
+permissions:
+  contents: read
+
+jobs:
+  clippy:
+    runs-on: ubuntu-latest
+    container: ghcr.io/xrplf/xrpld/nix-ubuntu:sha-a0074f8
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+
+      - name: Use cargo artifacts cache
+        uses: Swatinem/rust-cache@6323deb102c322ba6fcbdcafc7e3dddab59af2b6 # v2.9.2
+        with:
+          workspaces: crates
+
+      - name: Run clippy
+        run: cargo clippy --workspace --all-targets --all-features --locked -- -D warnings
+
+  coverage:
+    runs-on: ubuntu-latest
+    container: ghcr.io/xrplf/xrpld/nix-ubuntu:sha-a0074f8
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+
+      - name: Use cargo artifacts cache
+        uses: Swatinem/rust-cache@6323deb102c322ba6fcbdcafc7e3dddab59af2b6 # v2.9.2
+        with:
+          workspaces: crates
+
+      - name: Generate coverage report
+        run: cargo llvm-cov nextest --workspace --all-features --locked --no-tests=warn --lcov --output-path lcov.info
+
+      - name: Upload coverage report
+        if: ${{ github.repository == 'XRPLF/rippled' }}
+        uses: codecov/codecov-action@fb8b3582c8e4def4969c97caa2f19720cb33a72f # v7.0.0
+        with:
+          disable_search: true
+          disable_telem: true
+          fail_ci_if_error: true
+          files: crates/lcov.info
+          flags: rust
+          plugins: noop
+          token: ${{ secrets.CODECOV_TOKEN }}
+          verbose: true
+
+  doc:
+    runs-on: ubuntu-latest
+    container: ghcr.io/xrplf/xrpld/nix-ubuntu:sha-a0074f8
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+
+      - name: Use cargo artifacts cache
+        uses: Swatinem/rust-cache@6323deb102c322ba6fcbdcafc7e3dddab59af2b6 # v2.9.2
+        with:
+          workspaces: crates
+
+      - name: Build documentation
+        env:
+          RUSTDOCFLAGS: "-D warnings"
+        run: cargo doc --workspace --no-deps --all-features --locked

.gitignore

@@ -89,3 +89,6 @@ target/
 
 # clangd cache
 /.cache
+
+# Rust build directory
+crates/target

.pre-commit-config.yaml

@@ -62,6 +62,15 @@ repos:
         types_or: [c++, c, proto]
         exclude: ^include/xrpl/protocol_autogen/(transactions|ledger_entries)/
 
+  - repo: local
+    hooks:
+      - id: cargo-fmt
+        name: cargo fmt
+        entry: cargo fmt --manifest-path crates/Cargo.toml --all
+        language: system
+        types: [rust]
+        pass_filenames: false # rustfmt formats the whole workspace
+
   - repo: https://github.com/BlankSpruce/gersemi-pre-commit
     rev: e98930bdc210d3387007f9252d8c1694ea7e410f # frozen: 0.27.7
     hooks:

BUILD.md

@@ -304,6 +304,7 @@ See [Sanitizers docs](./docs/build/sanitizers.md) for more details.
 | ---------------- | ------------- | ----------------------------------------------------------------------------- |
 | `assert`         | OFF           | Force enabling assertions.                                                    |
 | `coverage`       | OFF           | Prepare the coverage report.                                                  |
+| `rust`           | OFF           | Build the Rust crates and the C++ code that depends on them.                  |
 | `tests`          | OFF           | Build tests.                                                                  |
 | `unity`          | OFF           | Configure a unity build.                                                      |
 | `verify_headers` | ON            | Make the `verify-headers` target available to compile each header on its own. |
@@ -316,6 +317,30 @@ memory) since they concatenate sources into fewer translation units. Non-unity
 builds may be faster for incremental builds, and can be helpful for detecting
 `#include` omissions.
 
+### Rust crates
+
+The Rust crates in `crates/` are only part of the build when `rust` is ON. With
+`-Drust=OFF` (the default) the `crates` directory is not added to the build, no
+cxxbridge bindings are generated, and the C++ tests that exercise the Rust
+interop are not compiled — so no Rust toolchain is needed. CI builds always pass
+`-Drust=ON`.
+
+With `-Drust=ON` you need one extra dependency: a Rust toolchain (`cargo`,
+`rustc`) matching the channel pinned in
+[`rust-toolchain.toml`](./rust-toolchain.toml), which compiles the crates and
+generates the cxxbridge bindings. It is provided by the
+[Nix development shell](./docs/build/nix.md), so `-Drust=ON` works there without
+any extra setup; otherwise install it as described in
+[Rust](./docs/build/environment.md#rust).
+
+The crates also have their own Rust unit tests. Those are run with `cargo` and
+need only the Rust toolchain, independently of CMake and of the `rust` option
+(CI runs them with `cargo nextest`):
+
+```bash
+cargo test --manifest-path crates/Cargo.toml --workspace
+```
+
 ### Verifying headers
 
 The regular build only compiles `.cpp` files, so a header is only ever checked

CMakeLists.txt

@@ -158,7 +158,13 @@ if(coverage)
     include(XrplCov)
 endif()
 
+add_custom_target(tidy_prerequisites)
+
+if(rust)
+    add_subdirectory(crates)
+endif()
 include(XrplCore)
+
 include(XrplProtocolAutogen)
 include(XrplInstall)
 include(XrplValidatorKeys)

CONTRIBUTING.md

@@ -225,8 +225,9 @@ environment, so you don't need to install most of the individual tools
 yourself. The version of each hook sourced from an external repository
 (`clang-format`, `gersemi`, etc.) is pinned in that file, so running the hooks
 locally uses exactly the same versions as CI. A few `local` hooks — most notably
-`clang-tidy` — run tools from your own environment; see
-[Installing clang-tidy](#installing-clang-tidy) for how to get those.
+`clang-tidy` and `cargo fmt` — run tools from your own environment; see
+[Installing clang-tidy](#installing-clang-tidy) and
+[Rust](./docs/build/environment.md#rust) for how to get those.
 
 To get started, install `pre-commit` and enable the git hook scripts:
 
@@ -255,6 +256,7 @@ The hooks configured in this repository include, among others:
 - `clang-tidy` — C++ static analysis (see [Clang-tidy](#clang-tidy)); opt in with `TIDY=1`
 - `fix-include-style`, `fix-pragma-once`, `check-doxygen-style` — C++ hygiene
 - `gersemi` — CMake formatting
+- `cargo fmt` — Rust formatting for the crates in `crates/`
 - `prettier`, `black`, `shfmt` — formatting for JavaScript/JSON/Markdown, Python, and shell
 - `cspell` — spell checking
 
@@ -319,7 +321,11 @@ See the [environment setup guide](./docs/build/environment.md#clang-tidy) for ho
 
 ### Running clang-tidy locally
 
-Before running clang-tidy, you must build the project to generate required files (particularly protobuf headers). Refer to [`BUILD.md`](./BUILD.md) for build instructions.
+Before running clang-tidy, you must generate the files it depends on (protobuf headers, and, when the project is configured with `-Drust=ON`, the cxxbridge headers from the Rust crates). Configure the project as described in [`BUILD.md`](./BUILD.md), then build the `tidy_prerequisites` target, which generates all of them:
+
+```bash
+cmake --build build --target tidy_prerequisites
+```
 
 #### Via pre-commit (recommended)
 

README.md

@@ -54,6 +54,7 @@ Here are some good places to start learning the source code:
 | `./docs`   | Source documentation files and doxygen config. |
 | `./cfg`    | Example configuration files.                   |
 | `./src`    | Source code.                                   |
+| `./crates` | Rust source code.                              |
 
 Some of the directories under `src` are external repositories included using
 git-subtree. See those directories' README files for more details.

cmake/XrplCore.cmake

@@ -51,6 +51,8 @@ target_compile_options(
 
 target_link_libraries(xrpl.libpb PUBLIC protobuf::libprotobuf gRPC::grpc++)
 
+add_dependencies(tidy_prerequisites xrpl.libpb)
+
 # TODO: Clean up the number of library targets later.
 add_library(xrpl.imports.main INTERFACE)
 

cmake/XrplSettings.cmake

@@ -32,6 +32,11 @@ endif()
 
 option(benchmark "Build benchmarks" ON)
 
+# When OFF, the crates directory is not added to the build at all: no Rust
+# toolchain is required, no cxxbridge bindings are generated, and the C++ tests
+# that consume those bindings are left out of the build tree.
+option(rust "Build the Rust crates and the C++ code that depends on them" OFF)
+
 # Enabled by default so every header is compiled on its own as the main file of
 # its own compile_commands.json entry - this is what lets clang-tidy (and clangd
 # and IDEs) analyse a header's own includes directly. The per-header objects are

conan.lock

@@ -23,6 +23,7 @@
         "fast_float/8.2.10#f6f28d6bb22112078e7dbda611caf681%1782494504.298",
         "ed25519/2015.03#ae761bdc52730a843f0809bdf6c1b1f6%1782307148.15562",
         "date/3.0.4#862e11e80030356b53c2c38599ceb32b%1782392402.538492",
+        "corrosion/0.6.1#bfa292df0a957bc70a450ff316cd9435%1786119416.131296",
         "c-ares/1.34.6#545240bb1c40e2cacd4362d6b8967650%1782392402.681654",
         "bzip2/1.0.8#c470882369c2d95c5c77e970c0c7e321%1782392402.296732",
         "boost/1.91.0#ea540ca2133d831b560036aa24dece3c%1782392419.475605",

conanfile.py

@@ -28,6 +28,7 @@ class Xrpl(ConanFile):
     }
 
     requires = [
+        "corrosion/0.6.1",
         "ed25519/2015.03",
         "fast_float/8.2.10",
         "grpc/1.81.1",

crates/.cargo/config.toml

@@ -0,0 +1,17 @@
+# The Rust static libraries are linked into C++ targets, so the runtime linkage
+# here has to match what the C++ build uses (see cmake/XrplCompiler.cmake).
+#
+# macOS needs nothing: AppleClang cannot link libgcc/libc++ statically, so the
+# C++ build skips those flags on Apple as well.
+
+# Both amd64 and arm64 Linux builds link libgcc statically. This only affects
+# links that rustc itself drives (`cargo test` binaries and the like) — the
+# `staticlib` crates consumed by CMake are archived, not linked, so rustc
+# silently ignores link args for them. Keeping libgcc_s.so.1 off the xrpld link
+# line is handled in crates/CMakeLists.txt instead.
+[target.'cfg(target_os = "linux")']
+rustflags = ["-C", "link-args=-static-libgcc"]
+
+# Windows builds use the static MSVC runtime.
+[target.'cfg(windows)']
+rustflags = ["-C", "target-feature=+crt-static"]

crates/CMakeLists.txt

@@ -0,0 +1,104 @@
+find_package(Corrosion REQUIRED)
+
+corrosion_import_crate(MANIFEST_PATH ${CMAKE_CURRENT_SOURCE_DIR}/Cargo.toml)
+
+# The generated C++ lands in the build tree, so put a .clang-tidy next to it to
+# keep clang-tidy from analyzing code we don't own.
+configure_file(
+    generated.clang-tidy
+    "${CMAKE_CURRENT_BINARY_DIR}/.clang-tidy"
+    COPYONLY
+)
+
+add_custom_target(xrpl_crates)
+add_dependencies(tidy_prerequisites xrpl_crates)
+
+# On macOS, ld warns `ignoring duplicate libraries` when linking a crate.
+# Corrosion is the source of both duplicates it names:
+#
+# * The crate archive and its cxxbridge archive, because
+#   `corrosion_add_cxxbridge` makes the two depend on each other, and CMake
+#   repeats a static library cycle on the link line so single-pass linkers can
+#   resolve it. (LINK_INTERFACE_MULTIPLICITY can only raise that count.)
+# * `-lSystem`, which Corrosion copies from rustc's `native-static-libs` even
+#   though the compiler driver always links libSystem.
+#
+# ld needs neither: it resolves the cycle from one copy of each archive and
+# links libSystem once. So silence the warning rather than rewrite Corrosion's
+# link interface, which the cycle is also part of. The option itself is old —
+# Xcode 15 is only where the warning became the default — and the check below
+# leaves it out on a linker that does not know it.
+if(is_macos)
+    include(CheckLinkerFlag)
+    check_linker_flag(
+        CXX
+        -Wl,-no_warn_duplicate_libraries
+        have_no_warn_duplicate_libraries
+    )
+endif()
+
+function(_unlink_libgcc_s crate)
+    if(NOT (is_linux AND static))
+        return()
+    endif()
+
+    # Corrosion exposes a crate's staticlib as an imported `<crate>-static`
+    # target and puts the native libs in its INTERFACE_LINK_LIBRARIES. If either
+    # of those changes, warn instead of silently letting libgcc_s.so.1 return.
+    set(imported "${crate}-static")
+    if(NOT TARGET ${imported})
+        message(
+            FATAL_ERROR
+            "Corrosion did not create the imported target '${imported}', so "
+            "libgcc_s cannot be removed from the link interface of '${crate}'. "
+            "xrpld will link libgcc_s.so.1 dynamically. Check where Corrosion "
+            "${CORROSION_VERSION} now records `native-static-libs`."
+        )
+        return()
+    endif()
+
+    get_target_property(libs ${imported} INTERFACE_LINK_LIBRARIES)
+    if(NOT "gcc_s" IN_LIST libs)
+        message(
+            WARNING
+            "'gcc_s' was not in the link interface of '${imported}' as "
+            "expected. If the Rust toolchain stopped reporting it this "
+            "workaround is obsolete and can be deleted; otherwise xrpld may "
+            "link libgcc_s.so.1 dynamically. Verify with: "
+            "objdump -p xrpld | grep NEEDED"
+        )
+        return()
+    endif()
+
+    list(REMOVE_ITEM libs gcc_s)
+    set_property(TARGET ${imported} PROPERTY INTERFACE_LINK_LIBRARIES ${libs})
+endfunction()
+
+function(add_xrpl_crate name)
+    cmake_parse_arguments(ARG "" "CRATE" "FILES" ${ARGN})
+    _unlink_libgcc_s(${ARG_CRATE})
+    # `cc` picks its runtime flag from `crt-static` alone, so it compiles a
+    # crate's C++ with `-MT`; Debug needs `-MTd` (to match cmake/XrplCompiler.cmake).
+    if(is_msvc)
+        corrosion_set_env_vars(
+            ${ARG_CRATE}
+            "$<$<CONFIG:Debug>:CXXFLAGS=-MTd>"
+        )
+    endif()
+    corrosion_add_cxxbridge(${name}_cxxbridge CRATE ${ARG_CRATE} FILES
+                            ${ARG_FILES}
+    )
+    # Generated cxxbridge headers don't exist at configure time; CMake 3.28+
+    # validates INTERFACE_SOURCES on consuming targets. Clear it to skip the
+    # existence check — build-time ordering is enforced by the custom commands.
+    set_target_properties(${name}_cxxbridge PROPERTIES INTERFACE_SOURCES "")
+    if(have_no_warn_duplicate_libraries)
+        target_link_options(
+            ${name}_cxxbridge
+            INTERFACE -Wl,-no_warn_duplicate_libraries
+        )
+    endif()
+    add_dependencies(xrpl_crates ${name}_cxxbridge)
+endfunction()
+
+add_xrpl_crate(rs_hello_world CRATE rs_hello_world FILES lib.rs)

crates/Cargo.lock

@@ -0,0 +1,301 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "anstyle"
+version = "1.0.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
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+
+[[package]]
+name = "cc"
+version = "1.2.61"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d16d90359e986641506914ba71350897565610e87ce0ad9e6f28569db3dd5c6d"
+dependencies = [
+ "find-msvc-tools",
+ "shlex",
+]
+
+[[package]]
+name = "clap"
+version = "4.6.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1ddb117e43bbf7dacf0a4190fef4d345b9bad68dfc649cb349e7d17d28428e51"
+dependencies = [
+ "clap_builder",
+]
+
+[[package]]
+name = "clap_builder"
+version = "4.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "714a53001bf66416adb0e2ef5ac857140e7dc3a0c48fb28b2f10762fc4b5069f"
+dependencies = [
+ "anstyle",
+ "clap_lex",
+ "strsim",
+]
+
+[[package]]
+name = "clap_lex"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c8d4a3bb8b1e0c1050499d1815f5ab16d04f0959b233085fb31653fbfc9d98f9"
+
+[[package]]
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+version = "0.13.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "af491d569909a7e4dee0ad7db7f5341fef5c614d5b8ec8cf765732aba3cff681"
+dependencies = [
+ "serde",
+ "termcolor",
+ "unicode-width",
+]
+
+[[package]]
+name = "cxx"
+version = "1.0.198"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6fe442a792c7c736eea18b32a7f8a3b63cf8aafabda6760042dc2fdeda456291"
+dependencies = [
+ "cc",
+ "cxx-build",
+ "cxxbridge-cmd",
+ "cxxbridge-flags",
+ "cxxbridge-macro",
+ "foldhash",
+ "link-cplusplus",
+]
+
+[[package]]
+name = "cxx-build"
+version = "1.0.198"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e3184a94384c663718698311a78a51ac00c484c10b4eeac06fb0a068c5f64fa2"
+dependencies = [
+ "cc",
+ "codespan-reporting",
+ "indexmap",
+ "proc-macro2",
+ "quote",
+ "scratch",
+ "syn 3.0.3",
+]
+
+[[package]]
+name = "cxxbridge-cmd"
+version = "1.0.198"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0148d8fd1199329ddf1d157a5e134e51ceff37c6a7ddd38615c399d81cb05d8d"
+dependencies = [
+ "clap",
+ "codespan-reporting",
+ "indexmap",
+ "proc-macro2",
+ "quote",
+ "syn 3.0.3",
+]
+
+[[package]]
+name = "cxxbridge-flags"
+version = "1.0.198"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "52850339faed2eaadd24e286dc1d8268cc6f8a7bd9524d713adc9099566b4c89"
+
+[[package]]
+name = "cxxbridge-macro"
+version = "1.0.198"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2c77c856545d886c9bd5215409ebb63b925e262135248b50c79e5a5f194ee47c"
+dependencies = [
+ "indexmap",
+ "proc-macro2",
+ "quote",
+ "syn 3.0.3",
+]
+
+[[package]]
+name = "equivalent"
+version = "1.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "877a4ace8713b0bcf2a4e7eec82529c029f1d0619886d18145fea96c3ffe5c0f"
+
+[[package]]
+name = "find-msvc-tools"
+version = "0.1.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5baebc0774151f905a1a2cc41989300b1e6fbb29aff0ceffa1064fdd3088d582"
+
+[[package]]
+name = "foldhash"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "77ce24cb58228fbb8aa041425bb1050850ac19177686ea6e0f41a70416f56fdb"
+
+[[package]]
+name = "hashbrown"
+version = "0.17.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4f467dd6dccf739c208452f8014c75c18bb8301b050ad1cfb27153803edb0f51"
+
+[[package]]
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+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d466e9454f08e4a911e14806c24e16fba1b4c121d1ea474396f396069cf949d9"
+dependencies = [
+ "equivalent",
+ "hashbrown",
+]
+
+[[package]]
+name = "link-cplusplus"
+version = "1.0.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7f78c730aaa7d0b9336a299029ea49f9ee53b0ed06e9202e8cb7db9bae7b8c82"
+dependencies = [
+ "cc",
+]
+
+[[package]]
+name = "proc-macro2"
+version = "1.0.106"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8fd00f0bb2e90d81d1044c2b32617f68fcb9fa3bb7640c23e9c748e53fb30934"
+dependencies = [
+ "unicode-ident",
+]
+
+[[package]]
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+checksum = "41f2619966050689382d2b44f664f4bc593e129785a36d6ee376ddf37259b924"
+dependencies = [
+ "proc-macro2",
+]
+
+[[package]]
+name = "rs-hello_world"
+version = "0.1.0"
+dependencies = [
+ "cxx",
+]
+
+[[package]]
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+source = "registry+https://github.com/rust-lang/crates.io-index"
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+
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+ "serde_core",
+ "serde_derive",
+]
+
+[[package]]
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+checksum = "41d385c7d4ca58e59fc732af25c3983b67ac852c1a25000afe1175de458b67ad"
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+ "serde_derive",
+]
+
+[[package]]
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+ "proc-macro2",
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+ "syn 2.0.117",
+]
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+source = "registry+https://github.com/rust-lang/crates.io-index"
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+
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+ "proc-macro2",
+ "quote",
+ "unicode-ident",
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+ "proc-macro2",
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+ "unicode-ident",
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+ "winapi-util",
+]
+
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+
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+checksum = "b4ac048d71ede7ee76d585517add45da530660ef4390e49b098733c6e897f254"
+
+[[package]]
+name = "winapi-util"
+version = "0.1.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c2a7b1c03c876122aa43f3020e6c3c3ee5c05081c9a00739faf7503aeba10d22"
+dependencies = [
+ "windows-sys",
+]
+
+[[package]]
+name = "windows-link"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f0805222e57f7521d6a62e36fa9163bc891acd422f971defe97d64e70d0a4fe5"
+
+[[package]]
+name = "windows-sys"
+version = "0.61.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ae137229bcbd6cdf0f7b80a31df61766145077ddf49416a728b02cb3921ff3fc"
+dependencies = [
+ "windows-link",
+]

crates/Cargo.toml

@@ -0,0 +1,15 @@
+[workspace]
+members = ["hello_world"]
+resolver = "3"
+
+[workspace.dependencies]
+cxx = { version = "1.0.198", features = ["c++20"] }
+
+[workspace.package]
+edition = "2024"
+
+[profile.release]
+opt-level = 3
+overflow-checks = true
+lto = true
+debug = true

crates/generated.clang-tidy

@@ -0,0 +1,10 @@
+---
+# Neutralizes clang-tidy for the corrosion/cxxbridge-generated C++. Copied into
+# the crates build directory by crates/CMakeLists.txt, next to the generated
+# sources, so clang-tidy picks it up instead of the top-level configuration.
+#
+# One check is kept enabled to avoid clang-tidy's "no checks enabled" error.
+Checks: "-*,google-readability-todo"
+WarningsAsErrors: ""
+HeaderFilterRegex: ""
+InheritParentConfig: false

crates/hello_world/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "rs-hello_world"
+version = "0.1.0"
+edition.workspace = true
+
+[lib]
+crate-type = ["staticlib"]
+
+[dependencies]
+cxx.workspace = true

crates/hello_world/src/lib.rs

@@ -0,0 +1,10 @@
+#[cxx::bridge(namespace = "rs::hello_world")]
+mod ffi {
+    extern "Rust" {
+        fn hello_world() -> String;
+    }
+}
+
+pub fn hello_world() -> String {
+    "hello_world".to_string()
+}

docs/build/environment.md

@@ -46,6 +46,9 @@ Besides a compiler, building `xrpld` requires:
 On Linux and macOS, the [Nix development shell](./nix.md) provides all of them
 (see below). On Windows they have to be installed manually.
 
+Building with `-Drust=ON` additionally requires a Rust toolchain, see
+[Rust](#rust). A default build does not, so it is not in the table above.
+
 Once they are in place, verify that everything is installed and runnable with:
 
 ```bash
@@ -121,6 +124,25 @@ manually:
 - [Git for Windows](https://git-scm.com/download/win)
 - Python, Conan, and CMake, at the versions listed in
   [Required tools](#required-tools).
+- a [Rust toolchain](https://rustup.rs) — only needed to build with
+  `-Drust=ON`, see [Rust](#rust)
+
+## Rust
+
+The repository contains a Rust workspace in [`crates/`](../../crates), whose
+crates are exposed to C++ through [cxx](https://cxx.rs) bindings. It is **not**
+part of a default build: the CMake `rust` option is OFF by default, and with it
+off no Rust toolchain is needed. It is only required when configuring with
+`-Drust=ON` (which is what CI does), see [Options](../../BUILD.md#options).
+
+The toolchain (`cargo`, `rustc`) is pinned to the channel in
+[`rust-toolchain.toml`](../../rust-toolchain.toml) at the repository root. If
+you install Rust with [rustup](https://rustup.rs), that file is picked up
+automatically, and `cargo`/`rustc` in the repository will use the pinned
+version.
+
+Everything else the Rust build needs on the CMake side comes from Conan along
+with the rest of the dependencies, so there is nothing further to install.
 
 ## Clang-tidy
 

docs/build/nix.md

@@ -128,6 +128,12 @@ Coverage builds (`-Dcoverage=ON`) work in the `gcc` shell (and `gcc-plain` on Li
 each ships a `gcov` matching its compiler, since Nix's cc-wrapper does not expose one.
 The `clang` shells do not include `llvm-cov`, so use a `gcc` shell for coverage.
 
+Builds of the Rust crates (`-Drust=ON`) also work out of the box: every shell
+provides the Rust toolchain pinned in
+[`rust-toolchain.toml`](../../rust-toolchain.toml) (see
+[Rust](./environment.md#rust)), plus the `cargo-audit`, `cargo-llvm-cov` and
+`cargo-nextest` plugins.
+
 ## Conan configuration
 
 The shell runs [`conan/init.sh`](../../conan/init.sh) on entry, so

src/tests/libxrpl/CMakeLists.txt

@@ -43,6 +43,9 @@ set(test_modules
 if(NOT WIN32)
     list(APPEND test_modules net)
 endif()
+if(rust)
+    target_link_libraries(xrpl_tests PRIVATE rs_hello_world_cxxbridge)
+endif()
 
 foreach(module IN LISTS test_modules)
     # Append the module's sources (${module}/*.cpp and ${module}.cpp, if any).
@@ -52,6 +55,12 @@ foreach(module IN LISTS test_modules)
         "${CMAKE_CURRENT_SOURCE_DIR}/${module}/*.cpp"
         "${CMAKE_CURRENT_SOURCE_DIR}/${module}.cpp"
     )
+    if(NOT rust)
+        # Tests of the Rust interop include generated cxxbridge headers, which
+        # do not exist without the crates, so keep them out of the build tree
+        # entirely. They are named `Rust<something>.cpp`.
+        list(FILTER sources EXCLUDE REGEX "/Rust[^/]*\\.cpp$")
+    endif()
     target_sources(xrpl_tests PRIVATE ${sources})
 
     # Expose the module's private headers under their canonical include path.

src/tests/libxrpl/basics/RustInterop.cpp

@@ -0,0 +1,9 @@
+#include <gtest/gtest.h>
+#include <rs_hello_world_cxxbridge/lib.h>
+
+#include <string>
+
+TEST(RustInteropTest, hello_world)
+{
+    EXPECT_EQ(std::string(rs::hello_world::hello_world()), "hello_world");
+}