ci: Workflow to build rust docs

Based on the beginnings of the twister build, but just then builds rust
docs.

Signed-off-by: David Brown <[email protected]>

.github/workflows/rustdoc-build.yml

@@ -0,0 +1,97 @@
+# Copyright (c) 2025 Linaro Limited
+# SPDX-License-Identifier: Apache-2.0
+
+name: Rust Documentation Build
+
+on:
+  schedule:
+    - cron: '0 */3 * * *'
+  push:
+    tags:
+      - v*
+  pull_request:
+
+permissions:
+  contents: read
+
+jobs:
+  generate-rust-docs:
+    runs-on:
+      group: zephyr-runner-v2-linux-x64-4xlarge
+    container:
+      image: ghcr.io/zephyrproject-rtos/ci-repo-cache:v0.27.4.20241026
+      options: '--entrypoint /bin/bash'
+    if: >
+      github.repository_owner == 'zephyrproject-rtos'
+    env:
+      BASE_REF: ${{ github.base_ref }}
+      CCACHE_DIR: /node-cache/ccache-zephyr
+      CCACHE_REMOTE_STORAGE: "redis://cache-*.keydb-cache.svc.cluster.local|shards=1,2,3"
+      CCACHE_REMOTE_ONLY: "true"
+      # `--specs` is ignored because ccache is unable to resolve the toolchain specs file path.
+      CCACHE_IGNOREOPTIONS: '-specs=* --specs=*'
+      LLVM_TOOLCHAIN_PATH: /usr/lib/llvm-16
+    steps:
+      - name: Apply container owner mismatch workaround
+        run: |
+          git config --global --add safe.directory ${GITHUB_WORKSPACE}
+
+      - name: Clone cached Zephyr repository
+        continue-on-error: true
+        run: |
+          git clone --shared /repo-cache/zephyrproject/zephyr .
+          git remote set-url origin ${GITHUB_SERVER_URL}/${GITHUB_REPOSITORY}
+
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          ref: ${{ github.event.pull_request.head.sha }}
+          fetch-depth: 0
+          persist-credentials: false
+
+      - name: Environment Setup
+        run: |
+          git config --global user.email "[email protected]"
+          git config --global user.name "Zephyr Bot"
+          rm -fr ".git/rebase-apply"
+          rm -fr ".git/rebase-merge"
+          git rebase origin/${BASE_REF}
+          git clean -f -d
+          git log  --pretty=oneline | head -n 10
+          west init -l . || true
+          west config manifest.group-filter -- +ci,+optional
+          west config --global update.narrow true
+          west update --path-cache /repo-cache/zephyrproject 2>&1 1> west.update.log || west update --path-cache /repo-cache/zephyrproject 2>&1 1> west.update.log || ( rm -rf ../modules ../bootloader ../tools && west update --path-cache /repo-cache/zephyrproject)
+          west forall -c 'git reset --hard HEAD'
+
+          echo "ZEPHYR_SDK_INSTALL_DIR=/opt/toolchains/zephyr-sdk-$( cat SDK_VERSION )" >> $GITHUB_ENV
+
+      - name: Set up ccache
+        run: |
+          mkdir -p ${CCACHE_DIR}
+          ccache -M 10G
+          ccache -p
+          ccache -z -s -vv
+
+      - name: Run rustdoc build
+        run: |
+          export ZEPHYR_BASE=${PWD}
+          export ZEPHYR_TOOLCHAIN_VARIANT=zephyr
+
+          # The || true is so this doesn't fail and we can try to figure out what is happening.
+          # todo: it should not be necessary to build first.
+          west build -b nrf52840dk/nrf52840 ../modules/lang/rust/docgen \
+            -DCMAKE_VERBOSE_MAKEFILE:BOOL=ON \
+            || true
+          # west build -t rustdoc
+          # west build -t rustdoc -b nrf52840dk/nrf52840 ../modules/lang/rust/docgen
+
+          pwd
+          ls -l
+          ls -l build
+          ls -l build/rust
+          echo 'sample'
+          cat build/rust/sample-cargo-config.toml
+
+          # Fail to look at what happened
+          exit 1