CI: Add job to show Tier 1 BSPs built on stable

.github/workflows/build-bsp.yml

@@ -13,10 +13,14 @@ jobs:
       uses: ./.github/actions/list-BSPs
 
   build:
-    # This name is matched against the project's branch protection settings
-    name: "build (${{matrix.bsp.name}}, ${{matrix.toolchain}})"
+    name: "${{matrix.bsp.name}} (Tier ${{matrix.bsp.tier}}, ${{matrix.toolchain}})"
     runs-on: ubuntu-latest
-    continue-on-error: ${{ matrix.toolchain == 'nightly' || matrix.bsp.tier != 1 }}
+    # There is a subtle difference between continue-on-error and setting
+    # strategy.fail-fast=false.  Both will allow all jobs to run to completion,
+    # however continue-on-error lets the next workflow stage run regardless of
+    # failed jobs, strategy.fail-fast=false will skip subsequent stages if any
+    # job fails.
+    continue-on-error: true
     needs: setup
     strategy:
       matrix: ${{fromJson(needs.setup.outputs.matrix)}}
@@ -39,8 +43,11 @@ jobs:
       run: |
         build_invocation=$(cat ./crates.json | jq -Mr --arg board '${{ matrix.bsp.name }}' -c '.boards | .[$board] | .build')
         set -ex
-        cd boards/${{ matrix.bsp.name }}
+        pushd boards/${{ matrix.bsp.name }}
         $(${build_invocation})
+        popd
+        mkdir -p output
+        touch "output/build"
 
     - name: Clippy ${{ matrix.bsp.name }}
       if: ${{ matrix.toolchain == 'nightly' }}
@@ -50,3 +57,41 @@ jobs:
         clippy_invocation=$(echo ${build_invocation} | sed 's/cargo build/cargo clippy/g')
         cd boards/${{ matrix.bsp.name }}
         $(${clippy_invocation})
+
+    - name: Done
+      uses: actions/upload-artifact@v4
+      with:
+        # name needs to be unique in the workspace
+        name: "${{ matrix.bsp.name }}-${{ matrix.toolchain }}"
+        path: output
+
+  check:
+    runs-on: ubuntu-latest
+    needs: build
+    steps:
+      # checkout needs to happen first, as it clears the working directory
+      - name: Checkout sources
+        uses: actions/checkout@v4
+      - name: Download artifacts
+        uses: actions/download-artifact@v4
+        with:
+          path: successful-jobs
+      - name: Tier 1 BSPs built on stable
+        run: |
+          tier_1_bsps=$(cat crates.json | jq -r -c '.boards | with_entries(select(.value.tier == 1)) | keys | join(" ")')
+
+          success="true"
+          for bsp in ${tier_1_bsps}; do
+            if [ -f successful-jobs/"${bsp}"-stable/build ]; then
+              echo "${bsp}" built on stable toolchain
+            else
+              echo "${bsp}" failed to build on stable toolchain
+              success="false"
+            fi
+          done
+
+          if [ ${success} = "true" ]; then
+            echo "Tier 1 BSPs all built on stable"
+          else
+            false
+          fi