add workflow to fetch spdx licenses

Includes trivial debug statement in cmd/main.go.

.github/workflows/fetch-licenses.yaml

@@ -0,0 +1,60 @@
+name: Fetch Licenses
+
+on:
+    workflow_dispatch:
+        inputs:
+            force_run:
+                description: 'Force run license extraction'
+                required: false
+                default: 'false'
+    schedule:
+        - cron: '0 0 * * *' # Runs at midnight ET
+    push:
+        branches: [elr/update-licenses]
+
+jobs:
+    fetch-licenses:
+        runs-on: ubuntu-latest
+
+        steps:
+            - name: Setup Git
+              run: |
+                  git config --global user.name "GitHub Actions"
+                  git config --global user.email "github-actions[bot]@users.noreply.github.com"
+    
+            - name: Checkout this repository's auto-update-licenses branch
+              uses: actions/checkout@v2
+
+            - name: Checkout official SPDX Repository
+              uses: actions/checkout@v2
+              with:
+                  repository: spdx/license-list-data
+                  path: official-spdx-licenses # creates a tmp dir to hold the SPDX licenses from the official repo
+
+            - name: Copy Licenses
+              run: |
+                  cp official-spdx-licenses/json/licenses.json cmd/licenses.json
+                  cp official-spdx-licenses/json/exceptions.json cmd/exceptions.json
+
+            - name: Check for changes
+              run: |
+                  git diff --exit-code -- cmd/licenses.json cmd/exceptions.json || exit 0
+                
+            - name: Run license extraction
+              run: |
+                  cd cmd
+                  echo "Current branch: $(git branch)"
+                  go run . extract -l -e
+                  cd ..
+                  git log --oneline -n 5
+
+            - name: Create Pull Request
+              uses: peter-evans/create-pull-request@v3
+              with:
+                  token: ${{ secrets.GITHUB_TOKEN }}
+                  commit-message: Add updated license files
+                  branch: auto-update-licenses
+                  base: main
+                  title: "Update SPDX license files"
+                  body: "The files in this PR are auto-generated by the [fetch-licenses](./.git/workflows/fetch-license.yaml) workflow when it runs the `cmd/extract` script.  It updates SPDX licenses based on the latest released set in the [spdx/license-list-data](https://github.com/spdx/license-list-data) repository maintained by [SPDX](https://spdx.org/licenses/).  \n\nTODO: [spdxexp/spdxlicenses/license_ranges.go](./spdxexp/spdxlicenses/license_range.go) has to be updated manually."
+                  labels: 'auto-update,licenses'

cmd/main.go

@@ -53,6 +53,7 @@ func main() {
 				os.Exit(1)
 			}
 			fmt.Println("Done!")
+			fmt.Println("---------------------------")
 		}
 	default:
 		writeHelpMessage()