ci: check every PR against baseline versions of deps

.github/workflows/pr.yml

@@ -22,7 +22,7 @@ on:
 
 jobs:
   lint:
-    name: 'lint & typecheck & test (Python ${{ matrix.python }})'
+    name: "lint & typecheck & test (Python ${{ matrix.python }}${{ matrix.baseline && ', baseline deps' || '' }}${{ matrix.experimental && ', experimental' || '' }})"
     runs-on: ubuntu-latest
     continue-on-error: ${{ matrix.experimental }}
     strategy:
@@ -33,9 +33,14 @@ jobs:
           - '3.11'
           - '3.12'
         experimental: [false]
+        baseline: [false]
         include:
           - python: '3.13'
+            baseline: false
             experimental: true
+          - python: '3.10'
+            baseline: true
+            experimental: false
     steps:
       - uses: actions/checkout@v4
       - name: Install Poetry
@@ -46,6 +51,9 @@ jobs:
           cache: poetry
       - name: Install deps
         run: poetry install --with=dev
+      - name: Replace deps with baseline versions
+        if: matrix.baseline
+        run: ./scripts/install-baseline-deps.sh
       - name: Lint with ruff
         run: poetry run ruff check
       - name: Type-check with mypy

scripts/install-baseline-deps.sh

@@ -0,0 +1,26 @@
+#!/bin/bash
+
+set -e
+
+MY_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+
+main() {
+    local requirements_file="$MY_DIR/requirements.baseline.txt"
+
+    # Install pygit2 build deps -- prebuilt 1.6.1 wheels on PyPI are only
+    # available for Python up to 3.9.
+    export DEBIAN_FRONTEND=noninteractive
+    export DEBCONF_NONINTERACTIVE_SEEN=true
+    sudo apt-get update -qqy
+    sudo apt-get install -qqy libgit2-dev
+
+    # Workaround https://github.com/yaml/pyyaml/issues/724 because we need
+    # exactly this version of PyYAML for faithful reproduction of the baseline
+    # environment.
+    poetry run pip install 'Cython<3'
+    poetry run pip install --no-build-isolation 'PyYAML==5.4.1'
+
+    poetry run pip install -r "$requirements_file"
+}
+
+main "$@"

scripts/requirements.baseline.txt

@@ -0,0 +1,13 @@
+# Package versions provided by Ubuntu 22.04 LTS.
+arpy==1.1.1
+certifi==2020.6.20
+jinja2==3.0.3
+packaging==21.3
+pygit2==1.6.1
+# pyyaml==5.4.1  # https://github.com/yaml/pyyaml/issues/724
+requests==2.25.1
+rich==11.2.0
+semver==2.10.2
+tomli==1.2.2
+tomlkit==0.9.2
+typing_extensions==3.10.0.2