CI: Update formatting actions to use git diff filter before formatting

Using git's diff-filter when checking for changed files allows the
actions to ignore any deleted files. Combined with explicitly passing
glob expressions for source files to git directly allows the command
to yield a list of changed files compatible with a given formatter
directly.

.github/actions/check-changes/action.yaml

@@ -3,7 +3,7 @@ description: Checks for changed files compared to specific git reference and glo
 inputs:
   baseRef:
     description: Git reference to check against
-    required: true
+    required: false
   ref:
     description: Git reference to check with
     required: false
@@ -15,12 +15,16 @@ inputs:
     description: Use fallback compare against prior commit
     required: false
     default: 'true'
+  diffFilter:
+    description: git diff-filter string to use
+    required: false
+    default: ''
 outputs:
   hasChangedFiles:
     value: ${{ steps.checks.outputs.hasChangedFiles }}
     description: True if specified files were changed in comparison to specified git reference
   changedFiles:
-    value: ${{ toJSON(steps.checks.outputs.changedFiles) }}
+    value: ${{ steps.checks.outputs.changedFiles }}
     description: List of changed files
 runs:
   using: composite
@@ -31,26 +35,42 @@ runs:
       env:
         GIT_BASE_REF: ${{ inputs.baseRef }}
         GIT_REF: ${{ inputs.ref }}
+        GITHUB_EVENT_FORCED: ${{ github.event.forced }}
+        GITHUB_REF_BEFORE: ${{ github.event.before }}
         USE_FALLBACK: ${{ inputs.useFallback }}
+        DIFF_FILTER: ${{ inputs.diffFilter }}
       run: |
         : Check for Changed Files ✅
         if [[ "${RUNNER_DEBUG}" ]]; then set -x; fi
         shopt -s extglob
         shopt -s dotglob
 
-        if ! git cat-file -e "${GIT_BASE_REF}" &> /dev/null; then
-          echo "::warning::Provided base reference ${GIT_BASE_REF} is invalid"
-          if [[ "${USE_FALLBACK}" == 'true' ]]; then
-            GIT_BASE_REF='HEAD~1'
+        if [[ "${GIT_BASE_REF}" ]]; then
+          if ! git cat-file -e "${GIT_BASE_REF}" &> /dev/null; then
+            echo "::warning::Provided base reference ${GIT_BASE_REF} is invalid"
+            if [[ "${USE_FALLBACK}" == 'true' ]]; then
+              GIT_BASE_REF='HEAD~1'
+            fi
           fi
+        else
+          if ! git cat-file -e ${GITHUB_REF_BEFORE} &> /dev/null; then
+            GITHUB_REF_BEFORE='4b825dc642cb6eb9a060e54bf8d69288fbee4904'
+          fi
+
+          GIT_BASE_REF='HEAD~1'
+          case "${GITHUB_EVENT_NAME}" in
+            pull_request) GIT_BASE_REF="origin/${GITHUB_BASE_REF}" ;;
+            push) if [[ "${GITHUB_EVENT_FORCED}" != 'true' ]]; then GIT_BASE_REF="${GITHUB_REF_BEFORE}"; fi ;;
+            *) ;;
+          esac
         fi
 
-        changes=($(git diff --name-only ${GIT_BASE_REF} ${GIT_REF} -- ${{ inputs.checkGlob }}))
+        changes=($(git diff --name-only --diff-filter="${DIFF_FILTER}" ${GIT_BASE_REF} ${GIT_REF} -- ${{ inputs.checkGlob }}))
 
         if (( ${#changes[@]} )); then
           file_string="${changes[*]}"
           echo "hasChangedFiles=true" >> $GITHUB_OUTPUT
-          echo "changedFiles=[${file_string// /,}]" >> GITHUB_OUTPUT
+          echo "changedFiles=[\"${file_string// /\",\"}\"]" >> $GITHUB_OUTPUT
         else
           echo "hasChangedFiles=false" >> $GITHUB_OUTPUT
           echo "changedFiles=[]" >> GITHUB_OUTPUT