CI: Cache Python venv (#7879)

This is smallish and mostly static, should cache well, avoid setup cost.

.github/actions/setup-venv/action.yml

@@ -0,0 +1,55 @@
+---
+# DESCRIPTION: Github actions composite action
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+name: Set up Python venv
+description: >-
+  Restore, create, and optionally save the make-managed Python venv in a GitHub
+  Actions cache. The cache key combines the venv path (venvs are not
+  relocatable), the host OS and version, the Python major.minor version, and
+  the python-dev-requirements.txt hash, so any of those changing invalidates
+  it. Requires the already-configured Verilator tree to be present in 'repo'.
+
+inputs:
+  repo:
+    description: "Verilator checkout holding the Makefile and .venv"
+    required: false
+    default: repo
+  save:
+    description: "Save the cache on a miss (set true only on trusted branches)"
+    required: false
+    default: 'false'
+
+runs:
+  using: composite
+  steps:
+    - name: Compute Python venv cache key
+      id: cachekey
+      shell: bash
+      working-directory: ${{ inputs.repo }}
+      run: |
+        source ci/ci-common.bash
+        host="${DISTRO_ID:-$HOST_OS}${DISTRO_VERSION:+-$DISTRO_VERSION}"
+        pyver="$(python3 -c 'import sys; print("%d.%d" % sys.version_info[:2])')"
+        reqs="$(sha256sum python-dev-requirements.txt | cut -d' ' -f1)"
+        venv="${PWD#/}/.venv"  # absolute venv path (leading '/' trimmed)
+        echo "key=venv-${host}-py${pyver}-${reqs}-${venv//\//-}" >> "$GITHUB_OUTPUT"
+
+    - name: Restore Python venv
+      id: venv
+      uses: actions/cache/restore@55cc8345863c7cc4c66a329aec7e433d2d1c52a9  # v5
+      with:
+        path: ${{ inputs.repo }}/.venv
+        key: ${{ steps.cachekey.outputs.key }}
+
+    - name: Create Python venv
+      shell: bash
+      working-directory: ${{ inputs.repo }}
+      run: make venv
+
+    - name: Save Python venv
+      if: ${{ inputs.save == 'true' && steps.venv.outputs.cache-hit != 'true' }}
+      uses: actions/cache/save@55cc8345863c7cc4c66a329aec7e433d2d1c52a9  # v5
+      with:
+        path: ${{ inputs.repo }}/.venv
+        key: ${{ steps.venv.outputs.cache-primary-key }}

.github/workflows/format.yml

@@ -11,6 +11,10 @@ on:
 permissions:
   contents: write
 
+defaults:
+  run:
+    working-directory: repo
+
 jobs:
   format:
     runs-on: ubuntu-24.04
@@ -19,21 +23,32 @@ jobs:
       - name: Checkout
         uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0  # v7
         with:
+          path: repo
           token: ${{ secrets.GITHUB_TOKEN }}
+
       - name: Install packages for build
         run: |
           sudo apt install clang-format-18 || \
           sudo apt install clang-format-18
           git config --global user.email "action@example.com"
           git config --global user.name "github action"
-      - name: Format code
+
+      - name: Configure
         run: |
           autoconf
           ./configure
-          make venv
+
+      - name: Set up Python venv
+        uses: ./repo/.github/actions/setup-venv
+        with:
+          save: ${{ github.ref == 'refs/heads/master' }}
+
+      - name: Format code
+        run: |
           source .venv/bin/activate
           make -j 4 format CLANGFORMAT=clang-format-18
           git status
+
       - name: Push
         run: |-
           if [ -n "$(git status --porcelain)" ]; then

.github/workflows/reusable-lint-py.yml

@@ -23,19 +23,21 @@ jobs:
         with:
           path: repo
 
-      - name: Install packages for build
-        run: ./ci/ci-install.bash build
+      - name: Install dependencies
+        run: |
+          ./ci/ci-install.bash build
+          sudo apt install python3-clang || \
+          sudo apt install python3-clang
 
       - name: Configure
         run: |
           autoconf
           ./configure --enable-longtests --enable-ccwarn
 
-      - name: Install python dependencies
-        run: |
-          sudo apt install python3-clang || \
-          sudo apt install python3-clang
-          make venv
+      - name: Set up Python venv
+        uses: ./repo/.github/actions/setup-venv
+        with:
+          save: ${{ github.ref == 'refs/heads/master' }}
 
       - name: Lint
         run: |-

.github/workflows/reusable-test.yml

@@ -139,7 +139,11 @@ jobs:
       - name: Install test dependencies
         run: |
           ./ci/ci-install.bash test
-          make venv
+
+      - name: Set up Python venv
+        uses: ./repo/.github/actions/setup-venv
+        with:
+          save: ${{ github.ref == 'refs/heads/master' }}
 
       - name: Test
         id: run-test

python-dev-requirements.txt

@@ -33,4 +33,4 @@ sphinxcontrib-spelling==8.0.2
 yamlfix==1.19.1
 yapf==0.43.0
 
-git+https://github.com/antmicro/astsee.git
+git+https://github.com/antmicro/astsee.git@222480a8ec13b312809ea4acc08c81b4c0f4da2f