feat(ci): introduce reusable user-config workflow

.github/workflows/build-user-config.yml

@@ -0,0 +1,96 @@
+name: Reusable user config build
+
+on: 
+  workflow_call:
+
+jobs:
+  matrix:
+    runs-on: ubuntu-latest
+    name: Fetch Build Keyboards
+    outputs:
+      matrix: ${{ steps.set-matrix.outputs.matrix }}
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Install yaml2json
+        run: python3 -m pip install remarshal
+      - id: set-matrix
+        name: Fetch Build Matrix
+        run: |
+          matrix=$(yaml2json build.yaml | jq -c .)
+          yaml2json build.yaml
+          echo "::set-output name=matrix::${matrix}"
+  build:
+    runs-on: ubuntu-latest
+    container:
+      image: zmkfirmware/zmk-build-arm:stable
+    needs: matrix
+    name: Build
+    strategy:
+      fail-fast: false
+      matrix: ${{fromJson(needs.matrix.outputs.matrix)}}
+    steps:
+      - name: Prepare variables
+        id: variables
+        run: |
+          if [ -n "${{ matrix.shield }}" ]; then
+            EXTRA_CMAKE_ARGS="-DSHIELD=${{ matrix.shield }}"
+            ARTIFACT_NAME="${{ matrix.shield }}-${{ matrix.board }}-zmk"
+            DISPLAY_NAME="${{ matrix.shield }} - ${{ matrix.board }}"
+          else
+            EXTRA_CMAKE_ARGS=
+            DISPLAY_NAME="${{ matrix.board }}"
+            ARTIFACT_NAME="${{ matrix.board }}-zmk"
+          fi
+          echo ::set-output name=extra-cmake-args::${EXTRA_CMAKE_ARGS}
+          echo ::set-output name=artifact-name::${ARTIFACT_NAME}
+          echo ::set-output name=display-name::${DISPLAY_NAME}
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Cache west modules
+        uses: actions/cache@v2
+        env:
+          cache-name: cache-zephyr-modules
+        with:
+          path: |
+            modules/
+            tools/
+            zephyr/
+            bootloader/
+            zmk/
+          key: ${{ runner.os }}-build-${{ env.cache-name }}-${{ hashFiles('manifest-dir/west.yml') }}
+          restore-keys: |
+            ${{ runner.os }}-build-${{ env.cache-name }}-
+            ${{ runner.os }}-build-
+            ${{ runner.os }}-
+      - name: West Init
+        run: west init -l config
+      - name: West Update
+        run: west update
+      - name: West Zephyr export
+        run: west zephyr-export
+      - name: West Build (${{ steps.variables.outputs.display-name }})
+        run: |
+          west build -s zmk/app -b ${{ matrix.board }} -- -DZMK_CONFIG=${GITHUB_WORKSPACE}/config ${{ steps.variables.outputs.extra-cmake-args }} ${{ matrix.cmake-args }}
+      - name: ${{ steps.variables.outputs.display-name }} DTS File
+        if: ${{ always() }}
+        run: |
+          if [ -f "build/zephyr/${{ matrix.board }}.dts.pre.tmp" ]; then cat -n build/zephyr/${{ matrix.board }}.dts.pre.tmp; fi
+          if [ -f "build/zephyr/zephyr.dts" ]; then cat -n build/zephyr/zephyr.dts; fi
+      - name: ${{ steps.variables.outputs.display-name }} Kconfig file
+        run: cat build/zephyr/.config | grep -v "^#" | grep -v "^$"
+      - name: Rename artifacts
+        run: |
+          mkdir build/artifacts
+          if [ -f build/zephyr/zmk.uf2 ]
+          then
+            cp build/zephyr/zmk.uf2 "build/artifacts/${{ steps.variables.outputs.artifact-name }}.uf2"
+          elif [ -f build/zephyr/zmk.hex ]
+          then
+            cp build/zephyr/zmk.hex "build/artifacts/${{ steps.variables.outputs.artifact-name }}.hex"
+          fi
+      - name: Archive (${{ steps.variables.outputs.display-name }})
+        uses: actions/upload-artifact@v2
+        with:
+          name: firmware
+          path: build/artifacts