Separate sdist build and dist validation job

.github/workflows/python-package.yml

@@ -1,5 +1,5 @@
 ---
-name: build
+name: Build and test
 
 on:  # yamllint disable-line rule:truthy
   push:
@@ -12,26 +12,18 @@ on:  # yamllint disable-line rule:truthy
 
 jobs:
 
-  build:
+  build-wheel:
     runs-on: ubuntu-latest
     outputs:
       darker-wheel-path: ${{ steps.get-darker-version.outputs.wheel-path }}
     steps:
       - uses: actions/checkout@v3
-        with:
-          fetch-depth: 0
       - uses: actions/setup-python@v3
-      - name: Upgrade pip, install wheel and twine
-        run: |
-          # strict dependency resolution added in pip 20.3
-          python -m pip install --upgrade 'pip>=20.3' wheel twine
-      - name: Build source distribution
-        run: python setup.py sdist
+      - name: Install wheel
+        run: python -m pip install wheel
       - name: Build wheel distribution
         run: python setup.py bdist_wheel
-      - name: Validate distributions
-        run: twine check dist/*
-      - name: Upload distributions for test jobs
+      - name: Upload wheel for other jobs
         uses: actions/upload-artifact@v3
         with:
           name: dist
@@ -60,13 +52,13 @@ jobs:
             python-version: python39
             # see https://github.com/cachix/install-nix-action/issues/135
     needs:
-      - build
+      - build-wheel
     steps:
       - uses: actions/checkout@v3
       - uses: cachix/install-nix-action@v17
         with:
           nix_path: nixpkgs=channel:nixos-21.11
-      - name: Download distributions made by the build job
+      - name: Download wheel uploaded by the build-wheel job
         uses: actions/download-artifact@v3
       - name: Run tests in nix-shell
         run: |
@@ -76,7 +68,7 @@ jobs:
             --run '
               python -m venv venv
               source venv/bin/activate
-              pip install "${{needs.build.outputs.darker-wheel-path}}[test]"
+              pip install "${{needs.build-wheel.outputs.darker-wheel-path}}[test]"
               pytest
             ' \
             ./default.nix
@@ -105,7 +97,7 @@ jobs:
             constraints: '--constraint constraints-future.txt'
             upgrade: '--upgrade --upgrade-strategy=eager'
     needs:
-      - build
+      - build-wheel
     steps:
       - uses: actions/checkout@v3
         with:
@@ -115,13 +107,28 @@ jobs:
         uses: actions/setup-python@v3
         with:
           python-version: ${{ matrix.python-version }}
-      - name: Download distributions made by the build job
+      - name: Download wheel uploaded by the build-wheel job
         uses: actions/download-artifact@v3
       - name: Install Darker and its dependencies from the wheel build earlier
         env:
           pip_options: ${{ matrix.upgrade }} ${{ matrix.constraints }}
         run: pip install ${pip_options}
-                 "${{needs.build.outputs.darker-wheel-path}}[test]"
+                 "${{needs.build-wheel.outputs.darker-wheel-path}}[test]"
       - name: Run Pytest
         run: |
           pytest --darker
+
+  build-sdist-validate-dists:
+    runs-on: ubuntu-latest
+    needs:
+      - build-wheel
+    steps:
+      - uses: actions/setup-python@v3
+      - name: Install twine
+        run: python -m pip install twine
+      - name: Download wheel uploaded by the build-wheel job
+        uses: actions/download-artifact@v3
+      - name: Build source distribution
+        run: python setup.py sdist
+      - name: Validate distributions
+        run: twine check dist/*