Add workflow for comparing schemas for changes

.github/workflows/compare.yaml

@@ -0,0 +1,75 @@
+name: Compare Schemas for Changes
+
+on:
+  push:
+    branches:
+      - main
+    tags:
+      - "*"
+  pull_request:
+
+jobs:
+  compare:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Check out repo
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+          path: current-ref
+
+      - name: Fetch origin main
+        run: cd $GITHUB_WORKSPACE/current-ref && git fetch origin main
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+          cache: "pip"
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip uv
+          uv pip install --system -r $GITHUB_WORKSPACE/current-ref/requirements.txt
+
+      - name: Set relative path to schema directory
+        run: |
+          echo "SCHEMA_DIR=python/lsst/sdm_schemas/schemas" >> $GITHUB_ENV
+
+      - name: Get list of changed YAML files
+        run: |
+          cd $GITHUB_WORKSPACE/current-ref
+          CHANGED_FILES=$(git diff --name-only origin/main..HEAD -- ${{ env.SCHEMA_DIR }} | sed "s|^${{ env.SCHEMA_DIR }}/||")
+          echo "Changed YAML files: $CHANGED_FILES"
+          echo "CHANGED_FILES=$CHANGED_FILES" >> $GITHUB_ENV
+
+      - name: Check out main branch
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+          ref: main
+          path: main-branch
+
+      - name: Run felis diff on the schema files
+        run: |
+          cd $GITHUB_WORKSPACE
+          for file in ${{ env.CHANGED_FILES }}; do
+            echo "Schema diff for $file:"
+            MAIN_FILE=main-branch/${{ env.SCHEMA_DIR }}/$file
+            CURRENT_FILE=current-ref/${{ env.SCHEMA_DIR }}/$file
+            felis diff $MAIN_FILE $CURRENT_FILE
+          done
+
+      - name: Run felis diff of schema file against database
+        run: |
+          cd $GITHUB_WORKSPACE
+          for file in ${{ env.CHANGED_FILES }}; do
+            echo "Database diff for $file:"
+            MAIN_FILE=main-branch/${{ env.SCHEMA_DIR }}/$file
+            DB_URL=sqlite:///$(basename ${MAIN_FILE%.yaml}).db
+            felis create $MAIN_FILE --engine-url $DB_URL
+            CURRENT_FILE=current-ref/${{ env.SCHEMA_DIR }}/$file
+            echo "Comparing $DB_URL to $CURRENT_FILE"
+            felis diff --engine-url $DB_URL $CURRENT_FILE
+          done