ci: also run the tests against the latest shfmt

.github/workflows/verify.yml

@@ -7,15 +7,45 @@ jobs:
 
     runs-on: ubuntu-latest
 
+    name: verify (node ${{ matrix.node-version }}, ${{ matrix.shfmt }} shfmt)
+
     strategy:
+      fail-fast: false
       matrix:
         node-version: [20.x, 22.x]
+        shfmt: [distro]
+        include:
+          # shfmt occasionally changes its output and its error messages, which
+          # the formatter tests assert on. The archive version lags well behind,
+          # so run one job against the latest release to catch such changes when
+          # they happen rather than when a user reports them.
+          - node-version: 22.x
+            shfmt: latest
 
     steps:
       - uses: actions/checkout@v4
 
-      - name: Install shellcheck and shfmt (used for testing)
-        run: sudo apt-get install -y shellcheck shfmt
+      - name: Install shellcheck (used for testing)
+        run: sudo apt-get install -y shellcheck
+
+      - name: Install shfmt from the Ubuntu archive (used for testing)
+        if: matrix.shfmt == 'distro'
+        run: sudo apt-get install -y shfmt
+
+      - name: Install the latest shfmt release (used for testing)
+        if: matrix.shfmt == 'latest'
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          tag=$(gh release view --repo mvdan/sh --json tagName --jq .tagName)
+          sudo curl -fsSL -o /usr/local/bin/shfmt \
+            "https://github.com/mvdan/sh/releases/download/$tag/shfmt_${tag}_linux_amd64"
+          sudo chmod +x /usr/local/bin/shfmt
+
+      - name: Show which shfmt is used
+        run: |
+          command -v shfmt
+          shfmt --version
 
       - uses: pnpm/action-setup@v4
         with:
@@ -34,7 +64,14 @@ jobs:
 
       - name: Publish coverage to codecov.io
         uses: codecov/codecov-action@v5
-        if: success() && matrix.node-version == '22.x'
+        if: success() && matrix.node-version == '22.x' && matrix.shfmt == 'distro'
         with:
           token: ${{ secrets.CODECOV_TOKEN }}
           files: ./codecov.yml
+
+  all-done:
+    needs:
+      - verify
+    runs-on: ubuntu-latest
+    steps:
+    - run: echo "All jobs completed"