Add a GitHub workflow to build through the build service.

The workflow isn't very specialised - it has been copied from the
template repository with just the names changed to allow it to
build properly.

However, as we're focusing on pull requests, the conditions have
been updated so that it triggers on the pull request not just on
the branch - this is important as otherwise it wouldn't trigger
when we create a PR from a fork.

.github/workflows/robuild.yaml

@@ -0,0 +1,118 @@
+---
+# RISC OS CI build through build.riscos.online
+#
+# To reuse this configuration with your own repository:
+#
+#   - Create a .robuild.yaml to describe what should be built on RISC OS.
+#       - `jobs.build.script` should be a list of commands to run on RISC OS
+#       - `jobs.build.artifacts.path` should be the directory to zip.
+#   - Create a VersionNum file if you wish to use the automated versioning
+#     in the same style as the RISC OS sources. [optional]
+#   - Update the 3rd step ('give the archive a versioned name') to give a
+#     suitable name for the archive.
+#   - Update the 4th step ('upload-artifacts') to include the same names.
+#
+# The 'release' job is triggered when a tag starting with a 'v' is created,
+# which will create a GitHub release for the repository with the name of the
+# version tag. The release will be a draft, and should be updated with
+# changes as you see fit.
+#
+
+name: RISC OS
+
+# Controls when the action will run. Triggers the workflow on:
+#   * push on any branch.
+#   * tag creation for tags beginning with a 'v'
+on:
+  push:
+    tags: ["v*"]
+  # Pull request events happen on pull request state transitions, and also when the PR is created.
+  pull_request:
+    branches: ["*"]
+
+jobs:
+  build-riscos:
+    # The type of runner that the job will run on
+    runs-on: ubuntu-latest
+
+    outputs:
+      version: ${{ steps.version.outputs.version }}
+      leafname: ${{ steps.version.outputs.leafname }}
+
+    # Steps represent a sequence of tasks that will be executed as part of the job
+    steps:
+      # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
+      - uses: actions/checkout@v2
+
+      - name: Obtain prerequisite build tool
+        run: |
+          # Fetch the build client
+          curl -s -L -o riscos-build-online https://github.com/gerph/robuild-client/releases/download/v0.05/riscos-build-online && chmod +x riscos-build-online
+
+      - name: Build through build.riscos.online
+        run: |
+          # Zip up the source to send to robuild
+          zip -q9r /tmp/source-archive.zip * .robuild.yaml
+          # Send the archive file to build service (timeout of 60 seconds)
+          ./riscos-build-online -i /tmp/source-archive.zip -a off -t 60 -o /tmp/built
+
+      - name: Give the output a versioned name
+        id: version
+        run: |
+          if [[ -f src/VersionNum ]] ; then
+              version=$(sed '/MajorVersion / ! d ; s/.*MajorVersion *"\(.*\)"/\1/' src/VersionNum)
+          else
+              version=$(git rev-parse --short HEAD)
+          fi
+          echo "This is version: $version"
+          leafname="WakeOnLAN-$version.zip"
+          if [ -f /tmp/built,a91 ] ; then
+              cp /tmp/built,a91 "WakeOnLAN-$version.zip"
+          else
+              echo "No archive was built?"
+              exit 1
+          fi
+          echo "::set-output name=version::$version"
+          echo "::set-output name=leafname::$leafname"
+
+      - uses: actions/upload-artifact@v2
+        with:
+          name: RISCOS-build
+          path: ${{ steps.version.outputs.leafname }}
+        # The artifact that is downloadable from the Actions is actually a zip of the artifacts
+        # that we supply. So it will be a regular Zip file containing a RISC OS Zip file.
+
+  # The release only triggers when the thing that was pushed was a tag starting with 'v'
+  release:
+    needs: build-riscos
+    runs-on: ubuntu-latest
+    if: startsWith(github.ref, 'refs/tags/v')
+    steps:
+      - name: Download built binary
+        uses: actions/download-artifact@v1
+        with:
+          name: RISCOS-build
+
+      - name: Create Release
+        id: create_release
+        uses: actions/create-release@v1
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          tag_name: ${{ github.ref }}
+          release_name: Release ${{ needs.build-riscos.outputs.version }}
+          draft: true
+          prerelease: false
+
+      - name: Upload Release Asset
+        id: upload-release-asset
+        uses: actions/upload-release-asset@v1
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          # This pulls from the CREATE RELEASE step above, referencing it's ID to get its outputs object, which include a `upload_url`.
+          # See this blog post for more info: https://jasonet.co/posts/new-features-of-github-actions/#passing-data-to-future-steps 
+          upload_url: ${{ steps.create_release.outputs.upload_url }}
+          asset_path: RISCOS-build/${{ needs.build-riscos.outputs.leafname }}
+          asset_name: ${{ needs.build-riscos.outputs.leafname }}
+          asset_content_type: application/zip